Abstract
Background
The composite index of inflammation and insulin resistance (IR), the C-reactive protein (CRP)–triglyceride–glucose (TyG) index (CTI), has been suggested to be closely associated with cardiovascular disease. However, the relationship between the CTI and kidney injury (KI), including its subtypes [declined kidney function (DKF) and proteinuria], remains unclear in patients with coronary heart disease (CHD), and whether sex differences exist is unknown.
Methods
This two-center cross-sectional study enrolled 3793 patients with CHD between September 2021 and May 2026. Multivariable stepwise-adjusted logistic regression assessed associations of the CTI with KI and its subtypes. Restricted cubic spline (RCS) analysis identified dose-response relationships and threshold effects, followed by piecewise comparisons. Subgroup analyses stratified by sex were performed to evaluate consistency across sexes. The area under the receiver operating characteristic curve (AUC), decision curve analysis (DCA), and the Boruta algorithm compared the discriminative performance of the CTI versus CRP and TyG alone for KI and its subtypes.
Results
Multivariable logistic regression showed that the CTI was significantly associated with KI and its subtypes in CHD patients. The overall prevalence of KI was 814/3,793 (21.5%). RCS revealed that CTI exceeding 4.8, 4.7, and 4.55, respectively, significantly increased risks of KI, DKF, and proteinuria. Notably, the increased risk of KI was particularly evident when CTI exceeded 4.45 in females and 4.96 in males. AUC, DCA, and Boruta rankings all confirmed stronger discriminative performance of the CTI than CRP or TyG alone for KI and its subtypes.
Conclusion
Elevated CTI was independently associated with KI and its subtypes in CHD patients, with clear threshold effects that differed by sex and superior discriminative performance to single indicators. These associations were more pronounced in overweight/obese patients. Although CTI may help identify individuals at higher risk, the sex-specific thresholds should be regarded as exploratory threshold estimates and require external validation before clinical application.
Keywords: coronary heart disease, C-reactive protein-triglyceride-glucose index, kidney injury, declined kidney function, proteinuria
Introduction
Kidney injury (KI), primarily manifested as reduced estimated glomerular filtration rate (eGFR) and/or proteinuria, is a common and clinically important comorbidity in patients with coronary heart disease (CHD).1–3 For brevity, this composite phenotype is referred to as KI in the present study; however, it was operationalized solely as a single measurement of eGFR <60 mL/min/1.73 m2 and/or proteinuria (24-hour urinary protein excretion >150 mg, or urinary albumin-to-creatinine ratio >30 mg/g). This definition does not denote acute kidney injury (AKI) or chronic kidney disease (CKD), because AKI requires a change in kidney function over a defined short interval and CKD requires persistence for at least 3 months; neither can be inferred from a single contemporaneous assessment. Long-term renal impairment can result in complications such as edema, hypertension, and cardiovascular disease (CVD).4,5 If persistently aggravated, it may progress to end-stage renal disease, involving multiple systems including the cardiovascular, skeletal, and hematopoietic systems, thereby significantly increasing the risk of mortality.6–9 CHD, a common chronic cardiovascular disorder particularly in middle-aged and elderly populations, often coexists with various chronic conditions.10,11 These high-risk patients also constitute the major population susceptible to reduced eGFR and/or proteinuria.12 Therefore, early detection, prevention, and intervention for KI in CHD patients hold substantial clinical and public health significance.
Previous strategies to mitigate KI in CHD patients have largely focused on traditional risk factors such as blood pressure (BP) and glycemic control.13–15 However, relying solely on these conventional approaches may be insufficient to adequately reduce the risk of KI. This is because CHD patients frequently experience a state of chronic low-grade inflammation and often present with insulin resistance (IR) secondary to obesity, diabetes, and hyperlipidemia.16,17 Accumulating basic research has highlighted the pivotal roles of inflammation and IR in the pathogenesis of KI.18–21 Chronic inflammation directly damages glomeruli, increases vascular permeability, and induces proteinuria.18,19,22 Concurrently, IR not only exacerbates inflammatory responses but also activates the renin-angiotensin-aldosterone system (RAAS), thereby imposing additional burdens on the kidneys.20,21 The synergistic effect of these two factors substantially elevates the risk of KI. Clinical evidence has also emerged. Studies in Chinese populations have shown that an elevated systemic inflammation response index (SIRI) is closely associated with CKD.23 Similarly, analyses in American populations have revealed that this index increases the risk of diabetic kidney disease in patients with type 2 diabetes mellitus (DM).24 Moreover, research on triglyceride glucose index (TyG)-related IR has confirmed its association with decreased kidney function (DKF) and the progression of CKD.25 These findings provide direct evidence linking inflammation and IR to KI.
Nevertheless, a single biomarker may not fully capture the complex pathophysiological interplay underlying these conditions. Recently, a novel composite index reflecting both inflammation and IR—the [C-reactive protein (CRP)-TyG index] (CTI)—has been developed.26,27 Conceptually, CRP reflects systemic inflammation, whereas TyG is a surrogate marker of IR and related metabolic dysregulation. These two processes are closely interconnected and may amplify each other; therefore, combining them into a composite index may capture inflammatory–metabolic crosstalk more comprehensively than either component alone and may provide incremental information beyond CRP or TyG alone. The CTI has demonstrated strong predictive capability in various diseases, including CVD, cardio-renal metabolic syndrome, sarcopenia, and depression.26–29 However, it remains unclear whether, in the specific high-risk population of CHD patients, the CTI is independently associated with KI and whether this association is stronger than that of either CRP or the TyG. Moreover, sex differences in this association have not been adequately explored. Such differences may be biologically and clinically plausible because sex hormones, body fat distribution, inflammatory responses, insulin sensitivity, renal hemodynamics, and the progression of renal impairment differ between women and men.30,31 These factors may influence how inflammation–IR-related indices relate to kidney injury, making sex-stratified analyses more than a purely statistical exploration.32 Therefore, this dual-center study was conducted to explore the association between the CTI and KI in CHD patients, including sex-stratified analyses to assess consistency across sexes, and to evaluate the discriminative performance of the CTI relative to CRP and TyG alone. The findings may provide evidence-based support for early KI monitoring and future risk stratification in this high-risk population. However, clinically useful CTI thresholds would require validation in independent populations before they could be considered for clinical risk stratification.
Materials and Methods
Study Design and Population
A total of 4255 patients with a confirmed diagnosis of CHD from the two centers were initially enrolled in this study. First, after excluding patients with missing data on fasting plasma glucose (FPG), triglycerides (TG), and CRP, which precluded the calculation of the CTI, 4126 patients remained for CTI calculation. Second, to assess KI, we further excluded those lacking data on estimated glomerular filtration rate (eGFR), 24-hour urinary protein excretion, or the urinary albumin-to-creatinine ratio (ACR). In addition, considering other potential confounding factors, we excluded patients with a prior diagnosis of end-stage renal disease, those who had received renal replacement therapy, and those with severe liver disease, malignancy, ongoing anti-infective therapy, or autoimmune diseases. Following these rigorous exclusion criteria, a total of 3793 patients were ultimately eligible for the study and included in the final analysis (Figure 1).
Figure 1.

Flowchart of patient enrollment and exclusion.
Covariate Information Collection
Covariate information in this study was collected from multiple sources, including medical visit records, electronic medical records, and patient interviews. First, basic anthropometric measurements were obtained by trained nurses, including height, weight, body mass index (BMI), systolic and diastolic blood pressure (SBP and DBP). Personal lifestyle habits, such as smoking and alcohol consumption, were acquired through structured interviews. Second, laboratory parameters were collected, encompassing liver function tests, total cholesterol (TC), TG, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and FPG. Based on these measurements, the eGFR was calculated using the CKD-EPI equation specific to the Chinese population.33–35 Third, information on medication use was recorded, including antiplatelet agents, lipid-lowering drugs, beta-blockers, and angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin receptor blockers (ARBs). Finally, medical history was obtained with a specific focus on the diagnoses of hypertension, diabetes mellitus, and hyperlipidemia (Supplementary Material).
Calculation of the CTI
Based on previous studies, the CTI was calculated using the following formula:26,27
CTI = 0.412 × Ln (CRP [mg/L]) + Ln (TG [mg/dL] × FPG [mg/dL])/2.
Outcomes
The primary outcome of this study was the occurrence of KI, defined as the presence of any of the following: 1) Decreased kidney function (DKF): eGFR <60 mL/min/1.73 m2; 2) Proteinuria: 24-hour urinary protein excretion >150 mg, or urinary ACR >30 mg/g. Participants meeting at least one of the above criteria were considered to have KI. This composite definition was intended to capture both impaired kidney function and markers of kidney damage. It does not denote acute kidney injury (AKI). Because eGFR and proteinuria/ACR were measured at a single time point in this cross-sectional study, we could not determine the duration of abnormalities or distinguish acute from chronic kidney disease.
Statistical Analysis
First, all patients with CHD were divided into three equal groups according to CTI tertiles, and comparisons of covariates were made across the three groups. Secondly, we conducted a collinearity diagnosis to determine whether all the variables had significant contributions (Table S1). To evaluate the independent associations of the CTI with KI and its subtypes (DKF and proteinuria), multivariable stepwise-adjusted logistic regression models were used, and trend tests were performed. Next, restricted cubic spline (RCS) analysis was employed to explore the dose–response relationship and potential threshold effects between the CTI and each outcome. To further validate the robustness of the findings, extensive subgroup analyses were conducted. Finally, to compare the diagnostic performance of the CTI with that of the individual indicators (CRP and TyG), we applied receiver operating characteristic (ROC) curves, decision curve analysis (DCA), and the Boruta algorithm—a machine-learning method for assessing variable importance. Detailed information on the statistical analyses is provided in the Supplementary Material.
R software (version 4.3.2) was used to perform all statistical analyses. Statistical significance was defined as a two-sided P value < 0.05.
Results
Comparison of Baseline Characteristics Among the Three CTI Groups
Table 1 presents the comparison of baseline characteristics among three groups of patients equally divided according to CTI tertiles (T1, T2, and T3). Compared with the T1 group (lowest CTI), the higher CTI groups (T2 and T3) exhibited a higher proportion of male patients but a relatively younger age. Regarding lifestyle factors, the rates of current smoking and alcohol consumption were significantly higher in the T2 and T3 groups. In terms of physiological parameters, both SBP and DBP were higher in the higher CTI groups than in the T1 group.
Table 1.
Comparison of Baseline Characteristics Across Tertiles of the CTI
| Characteristic | T1 (<4.56) | T2 (4.56–5.12) | T3 (>5.12) | P value |
|---|---|---|---|---|
| Numbers | 1265 | 1264 | 1264 | |
| Sex (%) | <0.001 | |||
| Female | 770 (60.87%) | 614 (48.58%) | 579 (45.81%) | |
| Male | 495 (39.13%) | 650 (51.42%) | 685 (54.19%) | |
| Age (years) | 67.31±10.74 | 64.44±10.64 | 64.06±11.07 | <0.001 |
| BMI (kg/m2) | 25.60±3.80 | 26.26±3.65 | 26.71±3.67 | <0.001 |
| SBP (mmHg) | 125.65±17.46 | 133.59±18.12 | 141.41±18.52 | <0.001 |
| DBP (mmHg) | 81.47±13.39 | 85.50±14.03 | 90.54±14.04 | <0.001 |
| Current smoking (%) | 277 (21.90%) | 369 (29.19%) | 404 (31.96%) | <0.001 |
| Current drinking (%) | 248 (19.60%) | 309 (24.45%) | 316 (25.00%) | 0.002 |
| Laboratory tests | ||||
| ALT (U/L) | 16.15 (11.40–23.75) | 18.00 (13.00–27.40) | 19.00 (13.82–27.00) | 0.001 |
| AST (U/L) | 17.10 (14.25–20.90) | 18.00 (15.00–22.00) | 18.90 (15.75–23.10) | <0.001 |
| TC (mmol/L) | 3.90±0.95 | 4.02±0.98 | 4.23±1.07 | <0.001 |
| TG (mmol/L) | 0.71 (0.59–0.88) | 0.91 (0.80–1.04) | 1.05 (0.93–1.21) | <0.001 |
| LDL-C (mg/dL) | 2.36±0.83 | 2.42±0.94 | 2.46±0.95 | 0.024 |
| HDL-C (mg/dL) | 1.39±0.35 | 1.30±0.34 | 1.26±0.34 | <0.001 |
| FPG (mmol/L) | 5.18±1.24 | 5.30±1.28 | 5.39±1.36 | <0.001 |
| eGFR (mL/min/1.73 m2) | 105.52±32.05 | 102.65±34.01 | 101.44±35.16 | 0.008 |
| CRP (mg/dL) | 2.74±2.68 | 3.02±2.63 | 6.61±9.07 | <0.001 |
| CTI | 3.97±0.38 | 4.69±0.14 | 5.19±0.24 | <0.001 |
| Medical history | ||||
| Hypertension (%) | 556 (43.95%) | 570 (45.09%) | 650 (51.42%) | <0.001 |
| DM (%) | 341 (26.96%) | 382 (30.22%) | 411 (32.52%) | 0.009 |
| Hyperlipidemia (%) | 251 (19.84%) | 273 (21.60%) | 297 (23.50%) | 0.083 |
| Medications | ||||
| Lipid-lowering drugs (%) | 1234 (97.55%) | 1252 (99.05%) | 1241 (98.18%) | 0.015 |
| Antiplatelet drugs (%) | 1237 (97.79%) | 1229 (97.23%) | 1230 (97.31%) | 0.632 |
| Beta-blockers (%) | 1232 (97.39%) | 1239 (98.02%) | 1251 (98.97%) | 0.013 |
| ACEIs/ARBs (%) | 872 (68.93%) | 887 (70.17%) | 943 (74.60%) | 0.004 |
Notes: Data are presented as mean ± standard deviation, median (interquartile range), or as numbers, and percentages.
Abbreviations: CTI, C-reactive protein-triglyceride-glucose index; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; ALT, alanine transaminase; AST, aspartate transaminase; LDL-C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein cholesterol; TC, total cholesterol; TG, triglyceride; FPG, fasting plasma glucose; eGFR, estimated glomerular filtration rate; CRP, C-reactive protein; DM, diabetes mellitus; ACEIs, angiotensin-converting enzyme inhibitors; ARBs, angiotensin receptor blockers.
Further analysis of laboratory findings revealed the following: first, liver function levels were significantly elevated in the higher CTI groups; second, regarding lipid metabolism, TC, TG, and LDL-C were markedly higher, whereas HDL-C was relatively lower; additionally, FPG and CRP levels increased with higher CTI, and the CTI itself was, by definition, higher; in contrast, eGFR was lower in the higher CTI groups.
With respect to medical history, the prevalence of hypertension and diabetes mellitus (DM) was significantly higher in the higher CTI groups compared with the T1 group. Regarding medication use, the rates of lipid-lowering drugs, beta-blockers, and ACEIs/ARBs were also higher in these groups. No significant differences were observed in the remaining variables across the three groups.
Association of the CTI with KI and Its Subtypes in Patients with CHD
Among the 3793 patients, 814 had KI. Table S2 shows the numbers of patients with KI and its subtypes. To investigate the association of the CTI with KI and its subtypes—DKF and proteinuria—in patients with CHD, we first divided the patients into three groups (T1, T2, T3) based on CTI tertiles and compared the prevalence of KI and its subtypes across the three groups. The results showed a gradually increasing trend in the prevalence of KI from the T1 to T3 group (Figure 2A). Similarly, for the two subtypes (DKF and proteinuria), both the T2 and T3 groups exhibited significantly higher prevalence than the T1 group, with the T3 group having the highest prevalence (Figure 2B and C).
Figure 2.

Prevalence of kidney injury and its subtypes by the three groups. (A) Kidney injury; (B) Decreased kidney function; (C) Proteinuria. Note (numbers): T1: 1265; T2: 1264; T3: 1264.
Logistic regression models were then used to evaluate the association between CTI and KI. In the unadjusted model (Model 1), each one-unit increase in CTI was associated with a 2.724-fold increased risk of KI (OR = 3.724, 95% CI: 3.149–4.421), and each one-standard deviation (SD) increase in CTI was associated with a 1.120-fold increased risk (OR = 2.120, 95% CI: 1.927–2.339) (Table 2). After full adjustment for covariates (Model 4), the association remained significant: each one-unit increase in CTI was associated with a 206.2% increased risk (OR = 3.062, 95% CI: 2.523–3.734), and each one-SD increase was associated with an 89.6% increased risk (OR = 1.896, 95% CI: 1.697–2.124). When CTI was analyzed as a categorical variable, the association became more explicit: compared with the T1 group, the T2 and T3 groups had a 63.4% (OR = 1.634) and 85.2% (OR = 1.852) higher risk of KI, respectively (Table 2).
Table 2.
Association of the CTI with Kidney Injury in Patients with CHD
| Kidney Injury | Model 1 | Model 2 | Model 3 | Model 4 |
|---|---|---|---|---|
| OR (95% CI) P | OR (95% CI) P | OR (95% CI) P | OR (95% CI) P | |
| CTI (per 1 increase) | 3.724 [3.149, 4.421] <0.001 | 3.717 [3.133, 4.428] <0.001 | 3.092 [2.553, 3.764] <0.001 | 3.062 [2.523, 3.734] <0.001 |
| CTI (per 1SD increase) | 2.120 [1.927, 2.339] <0.001 | 2.118 [1.921, 2.341] <0.001 | 1.907 [1.709, 2.133] <0.001 | 1.896 [1.697, 2.124] <0.001 |
| Tertile of CTI | ||||
| Tertile 1 | Reference | Reference | Reference | Reference |
| Tertile 2 | 1.847 [1.505, 2.271] <0.001 | 1.807 [1.468, 2.229] <0.001 | 1.689 [1.332, 2.145] <0.001 | 1.634 [1.294, 2.066] <0.001 |
| Tertile 3 | 2.308 [1.889, 2.827] <0.001 | 2.232 [1.820, 2.745] <0.001 | 1.868 [1.485, 2.356] <0.001 | 1.852 [1.466, 2.345] <0.001 |
| P for trend | <0.001 | <0.001 | <0.001 | <0.001 |
Notes: Model 1: no covariates were adjusted. Model 2: age, sex, BMI, smoking status, drinking status SBP, and DBP were adjusted. Model 3: Model 2 plus adjustment for ALT, AST, TC, TG, HDL-C, LDL-C, and FPG. Model 4: Model 3 plus adjustment for Hypertension, DM, Hyperlipidemia, Lipid-lowering drugs, antiplatelet drugs, beta-blockers, and ACEIs/ARBs.
Abbreviations: CTI, C-reactive protein-triglyceride-glucose index; CHD, coronary heart disease; OR, Odds Ratio; CI, confidence interval.
Similar findings were observed for the subtypes of KI. Each one-SD increase in CTI was associated with a 42.6% increased risk of DKF (OR = 1.426, 95% CI: 1.258–1.620) and an 81.7% increased risk of proteinuria (OR = 1.817, 95% CI: 1.591–2.084) (Table 3). When CTI was categorized by tertiles, the risk of both DKF and proteinuria also showed a graded increasing trend (P for trend < 0.01) (Table 3).
Table 3.
Association of the CTI with Subtypes of Kidney Injury in Patients with CHD
| Subtypes of Kidney Injury | Model 1 | Model 2 | Model 3 | Model 4 |
|---|---|---|---|---|
| OR (95% CI) P | OR (95% CI) P | OR (95% CI) P | OR (95% CI) P | |
| Decreased kidney function | ||||
| CTI (per 1 increase) | 2.572 [2.085, 3.190] <0.001 | 2.586 [2.088, 3.218] <0.001 | 1.885 [1.514, 2.358] <0.001 | 1.859 [1.493, 2.327] <0.001 |
| CTI (per 1SD increase) | 1.716 [1.522, 1.941] <0.001 | 1.721 [1.523, 1.950] <0.001 | 1.437 [1.268, 1.633] <0.001 | 1.426 [1.258, 1.620] <0.001 |
| Tertile of CTI | ||||
| Tertile 1 | Reference | Reference | Reference | Reference |
| Tertile 2 | 1.768 [1.333, 2.359] <0.001 | 1.767 [1.328, 2.366] <0.001 | 1.657 [1.219, 2.265] 0.001 | 1.550 [1.148, 2.104] 0.004 |
| Tertile 3 | 2.257 [1.719, 2.986] <0.001 | 2.238 [1.696, 2.975] <0.001 | 1.889 [1.401, 2.564] <0.001 | 1.835 [1.370, 2.472] <0.001 |
| P for trend | <0.001 | <0.001 | <0.001 | <0.001 |
| Proteinuria | ||||
| CTI (per 1 increase) | 4.117 [3.312, 5.149] <0.001 | 4.011 [3.216, 5.033] <0.001 | 2.938 [2.334, 3.722] <0.001 | 2.843 [2.252, 3.613] <0.001 |
| CTI (per 1SD increase) | 2.246 [1.983, 2.552] <0.001 | 2.212 [1.950, 2.519] <0.001 | 1.852 [1.623, 2.120] <0.001 | 1.817 [1.591, 2.084] <0.001 |
| Tertile of CTI | ||||
| Tertile 1 | Reference | Reference | Reference | Reference |
| Tertile 2 | 1.772 [1.360, 2.321] <0.001 | 1.683 [1.287, 2.212] <0.001 | 1.446 [1.084, 1.937] 0.013 | 1.445 [1.088, 1.928] 0.012 |
| Tertile 3 | 2.098 [1.620, 2.733] <0.001 | 1.964 [1.509, 2.570] <0.001 | 1.563 [1.183, 2.076] 0.002 | 1.512 [1.139, 2.018] 0.005 |
| P for trend | <0.001 | <0.001 | 0.003 | 0.008 |
Notes: Model 1: no covariates were adjusted. Model 2: age, sex, BMI, smoking status, drinking status SBP, and DBP were adjusted. Model 3: Model 2 plus adjustment for ALT, AST, TC, TG, HDL-C, LDL-C, and FPG. Model 4: Model 3 plus adjustment for Hypertension, DM, Hyperlipidemia, Lipid-lowering drugs, antiplatelet drugs, beta-blockers, and ACEIs/ARBs.
Abbreviations: CTI, C-reactive protein-triglyceride-glucose index; CHD, coronary heart disease; OR, Odds Ratio; CI, confidence interval.
Threshold Effect of CTI on KI and Its Subtypes (DKF and Proteinuria) in Patients with CHD
To further explore the dose–response relationship and potential threshold effects between the CTI and KI as well as its subtypes (DKF and proteinuria), we performed RCS analysis. The plotted curves revealed a nonlinear dose-dependent increase between the CTI and KI, DKF, and proteinuria (Figure 3). Moreover, specific thresholds were identified: 4.8 for KI, 4.7 for DKF, and 4.55 for proteinuria (Figure 3). These thresholds indicate that when the CTI exceeds 4.8, 4.7, and 4.55, respectively, the risk of KI, DKF, and proteinuria in patients with CHD increases significantly (Figure 3).
Figure 3.

Dose-response relationship of the CTI with kidney injury and its subtypes (decreased kidney function and proteinuria) in patients with CHD. (A) Kidney injury; (B) Decreased kidney function; (C) Proteinuria. Note: The solid line represents the fitted curve; the dashed lines on either side of the solid line represent the 95% confidence interval; the red dashed line represents the threshold.
Based on the identified cut-off points, we further conducted piecewise comparative analyses. The results showed that for KI, patients with a CTI > 4.8 had a 2.322-fold higher risk compared with those with a CTI ≤ 4.8 (Table 4). Similarly, for DKF, patients with a CTI > 4.7 had a 1.989-fold higher risk than those with a CTI ≤ 4.7, and for proteinuria, patients with a CTI > 4.55 had a 2.071-fold higher risk than those with a CTI ≤ 4.55 (Table 4).
Table 4.
Threshold Effects of the CTI on Kidney Injury and Its Subtypes in Patients with CHD
| CTI | Model 1 | Model 2 | Model 3 | Model 4 |
|---|---|---|---|---|
| OR (95% CI) P | OR (95% CI) P | OR (95% CI) P | OR (95% CI) P | |
| Kidney injury | ||||
| Turning point | 4.8 | 4.8 | 4.8 | 4.8 |
| <= 4.8 | Reference | Reference | Reference | Reference |
| > 4.8 | 2.975 [2.421, 3.668] <0.001 |
2.859 [2.321, 3.534] <0.001 |
2.372 [1.903, 2.965] <0.001 |
2.322 [1.857, 2.911] <0.001 |
| Decreased kidney function | ||||
| Turning point | 4.7 | 4.7 | 4.7 | 4.7 |
| <= 4.7 | Reference | Reference | Reference | Reference |
| > 4.7 | 2.601 [2.104, 3.231] <0.001 |
2.478 [1.998, 3.088] <0.001 |
2.040 [1.626, 2.572] <0.001 |
1.989 [1.579, 2.515] <0.001 |
| Proteinuria | ||||
| Turning point | 4.55 | 4.55 | 4.55 | 4.55 |
| <= 4.55 | Reference | Reference | Reference | Reference |
| > 4.55 | 2.771 [2.188, 3.543] <0.001 |
2.641 [2.077, 3.388] <0.001 |
2.109 [1.638, 2.737] <0.001 |
2.071 [1.603, 2.697] <0.001 |
Notes: Model 1: no covariates were adjusted. Model 2: age, sex, BMI, smoking status, drinking status SBP, and DBP were adjusted. Model 3: Model 2 plus adjustment for ALT, AST, TC, TG, HDL-C, LDL-C, and FPG. Model 4: Model 3 plus adjustment for Hypertension, DM, Hyperlipidemia, Lipid-lowering drugs, antiplatelet drugs, beta-blockers, and ACEIs/ARBs.
Abbreviations: CTI, C-reactive protein-triglyceride-glucose index; CHD, coronary heart disease; OR, Odds Ratio; CI, confidence interval.
We further performed sex-specific threshold analyses. The RCS curves showed that the risk of KI increased significantly when CTI exceeded 4.45 in females and 4.96 in males, suggesting that the optimal CTI threshold may differ by sex (Figure 4).
Figure 4.

Dose‑response relationships and threshold effects by sex.
Notes: CTI × sex interaction for KI: P = 0.144.
These threshold findings suggest that maintaining the CTI below the respective cut-off values may exert a protective effect against the risk of renal injury and its subtypes in patients with CHD.
Subgroup Analysis and Sensitivity Analysis
Given the individual differences among patients with CHD, including baseline characteristics, comorbidities, and medication use, which might have influenced the results to some extent, we conducted extensive subgroup analyses stratified by sex, age, BMI, current smoking status, alcohol consumption, presence of hypertension, DM, hyperlipidemia, and use of ACEIs/ARBs. The results remained consistent with the main findings, showing that elevated CTI was positively associated with KI and its subtypes (DKF and proteinuria) across all subgroups (Table 5). Importantly, the association was consistent in both male and female subgroups, indicating that the relationship between CTI and KI is not sex‑dependent.
Table 5.
Association of the CTI with Kidney Injury and Its Subtypes in Various Subgroup Analyses
| Subgroups | OR (95% CI) | P value | P for Interaction |
|---|---|---|---|
| Kidney Injury | |||
| Sex | 0.144 | ||
| Male | 3.358 (2.688–4.227) | <0.001 | |
| Female | 4.338 (3.362–5.648) | <0.001 | |
| Age (years) | 0.093 | ||
| <60 | 4.840 (3.492–6.811) | <0.001 | |
| ≥60 | 3.469 (2.853–4.241) | <0.001 | |
| BMI (kg/m2) | <0.001 | ||
| <24 | 1.364 (1.037–1.808) | 0.0284 | |
| ≥24 | 5.808 (4.676–7.266) | <0.001 | |
| Current smoking | 0.752 | ||
| No | 3.710 (3.061–4.522) | <0.001 | |
| Yes | 3.956 (2.816–5.647) | <0.001 | |
| Hypertension | 0.6105 | ||
| No | 3.615 (2.801–4.708) | <0.001 | |
| Yes | 3.953 (3.165–4.975) | <0.001 | |
| DM | 0.103 | ||
| No | 3.362 (2.756–4.126) | <0.001 | |
| Yes | 4.601 (3.384–6.352) | <0.001 | |
| Hyperlipidemia | 0.008 | ||
| No | 3.292 (2.736–3.981) | <0.001 | |
| Yes | 5.973 (4.060–8.991) | <0.001 | |
| ACEIs/ARBs | 0.201 | ||
| No | 2.927 (2.042–4.264) | <0.001 | |
| Yes | 3.840 (3.177–4.667) | <0.001 | |
| Decreased kidney function | |||
| Sex | 0.568 | ||
| Male | 2.481 (1.878–3.309) | <0.001 | |
| Female | 2.813 (2.041–3.919) | <0.001 | |
| Age (years) | 0.068 | ||
| <60 | 3.625 (2.405–5.563) | <0.001 | |
| ≥60 | 2.303 (1.805–2.960) | <0.001 | |
| BMI (kg/m2) | <0.001 | ||
| <24 | 1.142 (0.799–1.651) | 0.4732 | |
| ≥24 | 3.630 (2.792–4.758) | <0.001 | |
| Current smoking | 0.269 | ||
| No | 2.775 (2.172–3.570) | <0.001 | |
| Yes | 2.111 (1.404–3.230) | <0.001 | |
| Hypertension | 0.133 | ||
| No | 2.144 (1.567–2.969) | <0.001 | |
| Yes | 2.973 (2.252–3.965) | <0.001 | |
| DM | 0.127 | ||
| No | 2.281 (1.775–2.953) | <0.001 | |
| Yes | 3.273 (2.242–4.869) | <0.001 | |
| Hyperlipidemia | 0.191 | ||
| No | 2.362 (1.863–3.016) | <0.001 | |
| Yes | 3.323 (2.139–5.280) | <0.001 | |
| ACEIs/ARBs | 0.773 | ||
| No | 2.345 (1.465–3.846) | <0.001 | |
| Yes | 2.538 (2.010–3.226) | <0.001 | |
| Proteinuria | |||
| Sex | 0.081 | ||
| Male | 3.407 (2.541–4.622) | <0.001 | |
| Female | 5.058 (3.665–7.068) | <0.001 | |
| Age (years) | 0.408 | ||
| <60 | 4.851 (3.226–7.436) | <0.001 | |
| ≥60 | 3.942 (3.050–5.141) | <0.001 | |
| BMI (kg/m2) | <0.001 | ||
| <24 | 1.565 (1.069–2.330) | 0.0241 | |
| ≥24 | 5.695 (4.363–7.501) | <0.001 | |
| Current smoking | 0.079 | ||
| No | 3.727 (2.917–4.800) | <0.001 | |
| Yes | 6.023 (3.795–9.802) | <0.001 | |
| Hypertension | 0.289 | ||
| No | 4.816 (3.394–6.936) | <0.001 | |
| Yes | 3.770 (2.868–5.007) | <0.001 | |
| DM | 0.835 | ||
| No | 4.029 (3.095–5.292) | <0.001 | |
| Yes | 4.237 (2.899–6.314) | <0.001 | |
| Hyperlipidemia | 0.036 | ||
| No | 3.651 (2.873–4.674) | <0.001 | |
| Yes | 6.751 (4.081–11.542) | <0.001 | |
| ACEIs/ARBs | 0.287 | ||
| No | 3.104 (1.899–5.215) | <0.001 | |
| Yes | 4.211 (3.306–5.407) | <0.001 |
Note: CTI (per 1SD increase).
Abbreviations: CTI, C-reactive protein-triglyceride-glucose index; BMI, body mass index; DM, diabetes mellitus; ACEIs, angiotensin-converting enzyme inhibitors; ARBs, angiotensin receptor blockers; OR, Odds Ratio; CI, confidence interval.
Notably, BMI showed significant interactions across all three outcomes (P for interaction < 0.05). Specifically, the associations of CTI with KI and its subtypes were stronger in patients who were overweight or obese (BMI ≥ 24 kg/m2) and had hyperlipidemia (Table 5). This finding further emphasizes that overweight and obese patients with CHD should receive greater attention regarding their CTI levels, and timely monitoring and early intervention are warranted to reduce the risk of renal injury. Additionally, considering the possibility of overadjustment, we removed TG and FPG from the covariates adjusted for in Model 3 and repeated the model analyses; the results remained consistent (Table S3). Moreover, we further excluded patients with acute coronary syndrome and those with recent surgery to mitigate the potential influence of acute conditions and repeated the analyses; the results remained essentially unchanged (Table S4). Finally, because certain potential confounders, including prior use of various medications, could not be captured, we conducted an E-value analysis for unmeasured confounding. The E-value results suggested that unmeasured confounding was unlikely to explain away our findings (Table S5).
Comparison of the Diagnostic Performance of CTI versus Single Indicators (CRP and TyG) for KI and Its Subtypes
To further evaluate the discriminative performance of the CTI compared with the single indicators CRP and TyG for KI and its subtypes (DKF and proteinuria), we first performed ROC curve analysis and compared the areas under the curve (AUCs). The results showed that for KI, DKF, and proteinuria, the CTI yielded the highest AUC values (0.691, 0.655, and 0.703, respectively), indicating modest discriminative ability; these values were higher than those of CRP and TyG alone (Figure 5 and Table 6). Subsequently, DCA was used to assess the potential clinical utility, and the findings were consistent with the ROC analysis: the CTI also demonstrated the greatest net benefit for both KI and its subtypes (Figure 6). However, these DCA findings should be interpreted as exploratory and do not establish a diagnostic pathway or a clinical diagnostic reference standard. Finally, we applied the Boruta algorithm, a machine learning-based method for variable importance ranking. The results showed that compared with other covariates, the CTI consistently ranked among the top three in variable importance and was significantly higher than CRP and TyG (Figure 7). These findings provide variable-importance information and suggest that CTI may be a potentially useful variable for discrimination/classification, but they do not independently validate CTI as a clinical prediction or diagnostic tool. Collectively, these comparative analyses support that the CTI is an important factor associated with the concurrent presence of KI, DKF, and proteinuria in this cross-sectional study.
Figure 5.

Comparison of the area under the receiver operating characteristic curve between CTI and single indicators (CRP and TyG). (A) Kidney injury; (B) Decreased kidney function; (C) Proteinuria.
Table 6.
Comparison of the Diagnostic Performance of the CTI Versus Single Indicators (CRP and TyG) for Kidney Injury and Its Subtypes
| Outcomes | AUC | 95% CI low | 95% CI up | Accuracy | Specificity | Sensitivity | Positive-pv | Negative-pv |
|---|---|---|---|---|---|---|---|---|
| Kidney injury | ||||||||
| CTI | 0.691 | 0.668 | 0.714 | 0.668 | 0.692 | 0.588 | 0.363 | 0.849 |
| CRP | 0.566 | 0.543 | 0.588 | 0.659 | 0.738 | 0.363 | 0.278 | 0.810 |
| TyG | 0.676 | 0.654 | 0.698 | 0.723 | 0.787 | 0.488 | 0.385 | 0.849 |
| Decreased kidney function | ||||||||
| CTI | 0.655 | 0.626 | 0.684 | 0.736 | 0.770 | 0.469 | 0.204 | 0.920 |
| CRP | 0.565 | 0.534 | 0.595 | 0.689 | 0.724 | 0.386 | 0.139 | 0.911 |
| TyG | 0.625 | 0.594 | 0.656 | 0.733 | 0.767 | 0.435 | 0.177 | 0.922 |
| Proteinuria | ||||||||
| CTI | 0.703 | 0.678 | 0.728 | 0.665 | 0.668 | 0.649 | 0.220 | 0.929 |
| CRP | 0.558 | 0.528 | 0.587 | 0.803 | 0.878 | 0.224 | 0.194 | 0.897 |
| TyG | 0.692 | 0.664 | 0.719 | 0.736 | 0.762 | 0.534 | 0.227 | 0.926 |
Abbreviations: CTI, C-reactive protein-triglyceride-glucose index; CRP, C-reactive protein; TyG, triglyceride-glucose index; AUC, area under the curve; Positive-pv, positive predictive value; Negative-pv, negative predictive value.
Figure 6.

Comparison of decision curves between the CTI and single indicators (CRP and TyG). (A) Kidney injury; (B) Decreased kidney function; (C) Proteinuria.
Figure 7.

Boruta variable importance ranking. (A) Kidney injury; (B) Decreased kidney function; (C) Proteinuria.
Discussion
Traditionally, inflammation and IR have been recognized as core risk factors for the development and progression of CVD.16,36 However, accumulating evidence has recently revealed that these two pathological states also play critical roles in KI.37,38 Patients with CHD often experience a state of chronic low-grade inflammation and frequently present with IR secondary to obesity, diabetes, and hyperlipidemia, thereby subjecting their kidneys to a dual insult.16,39 Consequently, this high-risk population should not only be prioritized for cardiovascular event prevention but also be regarded as susceptible to KI. Given that impaired renal function further worsens cardiovascular outcomes, early monitoring and intervention for renal function in CHD patients are of great clinical importance.
To overcome the limitation that single indicators (eg, CRP or TyG) reflect only one aspect (inflammation or IR) and lack comprehensiveness, researchers have recently developed a novel composite index—the CTI—that integrates both dimensions.26,29 The CTI simultaneously assesses systemic inflammatory burden and IR and has demonstrated strong prognostic and predictive capabilities in various diseases, including CVD, stroke, sarcopenia, and depression.26–29 However, the association between the CTI and KI (including its subtypes, DKF and proteinuria) in CHD patients remains unexplored, and whether the CTI outperforms single indicators is unknown. To address this gap, the present study employed a dual‑center design to systematically investigate these associations. Our results showed that elevated CTI was significantly and positively associated with KI and its subtypes in CHD patients, with clear threshold effects: the cut‑off values for KI, DKF, and proteinuria were 4.8, 4.7, and 4.55, respectively. Subgroup analysis revealed that the adverse impact of elevated CTI was more pronounced in patients with BMI ≥ 24 kg/m2 (overweight or obese), highlighting the importance of maintaining CTI below the respective thresholds in this subgroup to reduce the risk of KI. Moreover, comparative analyses confirmed that the diagnostic performance of the CTI for KI and its subtypes was significantly superior to that of CRP or TyG alone. Importantly, sex‑specific threshold analyses revealed notable differences: the risk of KI increased when CTI exceeded 4.45 in females and 4.96 in males, indicating that the optimal CTI cut‑off for predicting KI differs between sexes. Despite these distinct thresholds, the positive association between CTI and KI was present in both male and female subgroups. These findings suggest that monitoring CTI levels in CHD patients—with consideration of sex‑specific thresholds—may facilitate early identification of high‑risk individuals and timely intervention.
Previous clinical studies have provided direct evidence supporting the independent roles of inflammation and IR in KI or CKD.23–25 For instance, studies in Chinese populations have shown that an elevated SIRI is closely associated with CKD, and analyses in American populations have revealed that this index increases the risk of diabetic kidney disease in patients with type 2 DM.23,24 Additionally, IR has been confirmed to be associated with declining renal function and progression of CKD.25,40,41 The TyG index, a surrogate marker of IR, has been demonstrated to be associated with renal function decline and CKD progression, and to mediate the obesity‑related risk of KI.25,40 However, most of these studies focused on a single pathological pathway without integrating both, and few have examined whether these associations differ by sex. Furthermore, no study has specifically investigated a composite index reflecting both inflammation and IR in the context of CHD—a population characterized by a high confluence of these two abnormalities. The present study is the first to validate an independent association between the CTI and renal injury in CHD patients, to identify threshold effects, to demonstrate stronger associations in the overweight/obese subgroup, and to show that these associations remain consistent across male and female subgroups, thereby filling an important evidence gap.
An elevated CTI reflects the coexistence of chronic inflammation and IR, which may synergistically promote KI in CHD patients through the following mechanisms: 1) Under chronic inflammation, pro‑inflammatory cytokines (eg, IL‑6, TNF‑α) directly damage glomerular endothelial cells, increase vascular permeability, and lead to proteinuria;42–44 2) Inflammation also induces podocyte injury and thickening of the glomerular basement membrane, further compromising filtration function;45–47 3) IR activates the RAAS, elevating intraglomerular pressure, exacerbating renal hemodynamic burden, and promoting tubulointerstitial fibrosis;48–50 4) IR is often accompanied by hyperinsulinemia, which stimulates renal tubular sodium reabsorption, leading to sodium and water retention and hypertension, thereby indirectly impairing renal function;51,52 5) Inflammation and IR amplify each other: inflammatory cytokines interfere with insulin signaling, worsening resistance, while insulin resistance, via metabolites such as free fatty acids, triggers inflammatory cascades, forming a vicious cycle;53,54 6) A high CTI also reflects lipid metabolic dysregulation; elevated triglycerides and glucose can directly damage renal tubular epithelial cells through lipotoxicity, oxidative stress, and mitochondrial dysfunction.55–57 Collectively, these mechanisms explain why the CTI outperforms single indicators in predicting KI.
This study has several major strengths: (1) The dual‑center design enhances sample representativeness and generalizability of the findings; (2) It is the first to employ the novel CTI that integrates inflammation and IR, focusing on the high‑risk CHD population, which represents a significant innovation; (3) Beyond the overall association with KI, the study separately examined two distinct subtypes (DKF and proteinuria), allowing for phenotypic refinement; (4) RCS analysis identified clear threshold effects, providing specific targets for clinical intervention; (5) Comprehensive validation was performed through subgroup analyses, interaction tests, and multiple diagnostic performance comparisons (ROC, DCA, Boruta algorithm), confirming the robustness of the results and the superiority of the CTI; (6) The conclusions directly inform early monitoring and high‑risk screening, offering strong clinical applicability.
Several limitations should be acknowledged: (1) As an observational study, causality between CTI and renal injury cannot be established; future prospective cohort or interventional studies are needed. (2) Despite adjustment for multiple confounders, residual confounding or unmeasured variables (dietary patterns, physical activity, and genetic background) may persist. (3) The CTI was based on a single blood measurement, failing to capture dynamic changes in inflammation and IR over time; the relationship between long‑term exposure and cumulative renal injury risk remains unclear. (4) The study population consisted exclusively of Chinese CHD patients; whether the CTI thresholds and other conclusions apply to other ethnicities or populations requires external validation. (5) KI was defined using eGFR and proteinuria markers; tubular injury biomarkers or renal biopsy data were not included. (6) Although the sample size was reasonably large, some subgroup analyses might have been underpowered, necessitating confirmation in larger studies.
Conclusion
In this dual-center study, higher CTI was independently associated with KI and its subtypes (DKF and proteinuria) in patients with CHD, with apparent nonlinear threshold effects (4.8, 4.7, and 4.55, respectively). These associations were stronger in overweight/obese patients (BMI ≥ 24 kg/m2), and CTI showed stronger discriminative performance for KI than CRP or TyG alone. Sex-specific associations were evident above 4.45 in female and 4.96 in male; these are exploratory threshold estimates, not established clinical cut-offs. Because CTI and renal outcomes were assessed at approximately the same time and CTI was based on a single measurement, these findings indicate association only and cannot establish temporal or causal relationships. Longitudinal studies with external validation are needed.
Funding Statement
No funding was received for this study.
Data Sharing Statement
The dataset generated and analyzed in this study is available upon reasonable request to the corresponding author.
Ethics Approval and Consent to Participate
This study was conducted in strict accordance with the ethical principles outlined in the Declaration of Helsinki. The study protocol was reviewed and approved by the Ethics Committees of both participating hospitals: Huangshan City People’s Hospital (HS-20219-08) and Xinxiang Central Hospital (2024-352). All participants were fully informed of the study objectives and procedures before the commencement of the study, and written informed consent was obtained from each participant voluntarily.
Author Contributions
Mengmeng Fan: Conceptualization, Methodology, Investigation, Data Curation, Formal Analysis, Writing – Original Draft, Writing – review and editing. Xueping Zhang: Conceptualization, Data Curation, Methodology, Investigation, Supervision, Data Curation, Writing – review and editing. Xianwei Tian: Methodology, Investigation, Data Curation, Writing – review and editing. Keli Li: Methodology, Data Curation, and Writing – review and editing. Zhiqiang Liu: Conceptualization, Data Curation, Methodology, Investigation, Supervision, Data Curation, Writing – Original Draft, Writing – review and editing. All authors gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.
Disclosure
The authors report no conflicts of interest in this work.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The dataset generated and analyzed in this study is available upon reasonable request to the corresponding author.
