This work is licensed under a Abstract
Objective
Chronic kidney disease (CKD) has been reported in association with hypercalcitoninemia, but the calcitonin (Ct) values to expect in CKD patients are unknown. This study aimed to evaluate Ct levels in CKD patients using an accurate chemiluminescent immunoassay.
Methods
Two population datasets were analyzed: Group 1 consisted of 9,450 anonymous subjects with Ct and creatinine measurements; this group was subdivided according to eGFR into a control series (eGFR ≥ 90 mL/min/1.73 m2, n = 4,294) and a CKD series (eGFR < 90 mL/min/1.73 m2, n = 4,022). Group 2 consisted of 135 patients with CKD (78.5% in stage 5). Renal function and Ct levels were retrospectively evaluated.
Results
The Group 1 CKD series had a median Ct of 1.0 ng/L (IQR: 1.0–2.8 ng/L), 181 patients (4.5%) had Ct > 10 ng/L and ≤30 ng/L, and 35 patients (0.9%) had Ct ≥ 30 ng/L. Median Ct differed significantly according to CKD stage: 1.00 ng/L (IQR: 1.00–2.40 ng/L) in stage 2; 1.20 ng/L (IQR: 1.00–4.30 ng/L) in stage 3; 2.80 ng/L (IQR: 1.00–6.75 ng/L) in stage 4; and 4.55 ng/L (IQR: 1.00–11.30 ng/L) in stage 5 (P < 0.001). Median Ct in the control series was 1.0 ng/L (IQR: 1.0–2.9 ng/L). Ct levels >10 ng/L were significantly associated with CKD stage and were observed in 16.7% of stage 4 patients and 31.1% of stage 5 patients vs 4.3% of controls (P < 0.001). In Group 1, Ct levels were significantly correlated with creatinine (P < 0.001). In Group 2, median Ct was 3.7 ng/L (IQR: 1.0–7.0 ng/L), 25 patients (18.5%) had Ct levels >10 ng/L, and Ct levels were not associated with renal function.
Conclusions
Ct levels may be mildly elevated in advanced CKD; until stage 3, the increase is negligible.
Keywords: calcitonin, CKD, non-neoplastic hypercalcitoninemia, CLIA
Introduction
Calcitonin (Ct) is a peptide hormone secreted by parafollicular C cells of the thyroid and is known to be the most sensitive marker of medullary thyroid carcinoma (MTC) (1). Ct levels may be mildly elevated in conditions other than C cell disease, being differential diagnosis between non-neoplastic hypercalcitoninemia and MTC pivotal in performing an adequate diagnostic workup. Significantly elevated Ct levels (>100 pg/mL) have a high positive predictive value in the diagnosis of MTC, whereas mildly elevated Ct levels require careful evaluation of the potential causes of non-neoplastic hypercalcitoninemia and further investigation (2).
Chronic autoimmune gastritis, autoimmune thyroiditis, smoking, use of proton pump inhibitors (PPI), and chronic kidney disease (CKD) are among the conditions that have been reported to lead to non-neoplastic hypercalcitoninemia (3, 4, 5). The impact of many of these conditions on Ct levels has recently been questioned now that more accurate assay kits for measuring Ct, such as chemiluminescent immunoassay (CLIA), are available in clinical practice (6, 7, 8). Previously used methods, such as radioimmunometric assays (RIAs), were less specific for Ct and prone to interference from Ct precursors, which could overestimate the measured level. Nonetheless, as with other biomarkers, Ct measurement is still prone to laboratory interference (3, 9, 10).
The vast majority of studies investigating the influence of CKD on Ct levels have been carried out using RIA methods (11, 12, 13, 14, 15), and Ct has rarely been measured with more accurate assays in this context (16, 17, 18, 19). Moreover, it is still not clear at which CKD stage Ct levels significantly rise, as it is difficult to evaluate the significance of mild Ct elevation in patients with CKD and thyroid nodular disease in clinical practice (16, 17, 18). The aim of our study was to evaluate Ct levels in patients with CKD using an accurate measuring method in order to investigate the association between Ct and glomerular filtration rate.
Materials and methods
Two separate datasets were compiled: a retrospective dataset of anonymous subjects (Group 1) and a retrospective clinical cohort of CKD patients being followed up at the Nephrology Unit of our hospital (Group 2).
Group 1 – anonymous subjects
The Laboratory Medicine Unit of the University Hospital of Padua provided us with anonymous data obtained from subjects whose Ct levels had been measured at the laboratory between 2013 and 2023. We included these measurements in our analyses only if a simultaneous creatinine measurement was also available. The subjects’ sex and age were also recorded. The data, which came from 9,450 blood samples, were collected retrospectively, anonymously, and consecutively.
Of the 9,450 blood samples, 413 samples with Ct levels >100 ng/L were excluded from the analysis as being highly suspicious for MTC. A further 721 were excluded because there were no corresponding glomerular filtration rates estimated by CKD-EPI. We analyzed the remaining 8,316 samples, of which 4,294 subjects with an estimated glomerular filtration rate (eGFR) ≥ 90 mL/min/1.73 m2 were assigned to the ‘control series’ and 4,022 with eGFR < 90 mL/min/1.73 m2 were assigned to the ‘CKD series’ (Fig. 1).
Figure 1.
Flow chart of the dataset of anonymous subjects (Group 1) provided by the Laboratory Medicine Unit of the University Hospital of Padua. eGFR, estimated glomerular filtration rate; CKD, chronic kidney disease.
Group 2 – clinical cohort of CKD patients
From April 2023 to June 2024, we consecutively enrolled patients with CKD in follow-up at the Nephrology Unit of the University Hospital of Padua and whose Ct, creatinine, and eGFR had been previously evaluated in a single blood test at the local laboratory. We also considered procalcitonin (proCt) levels and biochemical data on calcium–phosphate metabolism, where available.
The inclusion criteria were as follows:
CKD, stable for at least 3 months, with eGFR < 90 mL/min/1.73 m2;
written consent to participation in the study;
previous evaluation of plasma Ct levels by CLIA at the local Laboratory Unit.
The exclusion criteria were as follows:
diagnosis of autoimmune chronic gastritis;
previous or current diagnosis of neuroendocrine tumors;
age < 18 years.
We ultimately enrolled 135 patients and obtained their anthropometric, clinical, and biochemical data from clinical records. If patients’ Ct levels were above the laboratory upper limit of normality (10 ng/L), a second Ct measurement, where available, was also considered. In dialysis patients, pre-dialysis Ct measurement was considered.
This study was performed in accordance with the guidelines of the Declaration of Helsinki and approved by the Local Ethical Committee (Padua General Hospital, Comitato Etico per la Sperimentazione Clinica (CESC), ethics code number: 405n/AO/23). All patients in Group 2 gave written informed consent to participate in the study. No informed consent was necessary for Group 1 as the data were collected anonymously and contained nothing of a sensitive nature.
Laboratory
Ct levels were measured with a LIAISON® Calcitonin II-Gen CLIA kit (DiaSorin Inc., USA). The method has an analytical sensitivity of ≤1.0 ng/L, a functional sensitivity of ≤3.0 ng/L, and an upper reference limit of 10.0 ng/mL.
Procalcitonin levels were measured with a LIAISON BRAHMS PCT II-Gen CLIA kit (DiaSorin, Italy). Analytical sensitivity was 0.04 ng/mL, and the upper reference limit was 0.5 ng/mL.
Calcium and phosphate were measured using the colorimetric method (reference ranges: calcium 2.10–2.55 mmol/L; phosphate 0.87–1.45 mmol/L). PTH and 25-OH vitamin D were analyzed using the chemiluminescent method (reference ranges: PTH 6.5–36.8 ng/L; 25-OH vitamin D: 47.8–190.3 nmol/L). Plasma creatinine levels were measured using the enzymatic method, and eGFRs measured with the CKD-EPI method were provided by the laboratory. CKD stages were defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) classification based on eGFR, as follows (20):
stage 1: eGFR ≥ 90 mL/min/1.73 m2;
stage 2: eGFR 60–89 mL/min/1.73 m2;
stage 3: eGFR 30–59 mL/min/1.73 m2;
stage 4: eGFR 15–29 mL/min/1.73 m2;
stage 5: eGFR < 15 mL/min/1.73 m2.
All laboratory data were measured at the Laboratory Unit of the University Hospital of Padua.
Statistical analysis
The Kolmogorov–Smirnov test was used to assess the normal distribution of the variables. Normally distributed parameters were expressed as the arithmetic mean ± the standard deviation; non-normally distributed parameters were expressed as median, interquartile range (IQR), and range of minimum and maximum value. A P value < 0.05 was considered statistically significant. Ct was considered both a quantitative variable and a categorized variable, in the latter case as either ≤10 ng/L or >10 ng/L. ProCt was considered a quantitative variable and a categorized variable, in the latter case as either ≤0.04 ng/mL or >0.04 ng/mL. Creatinine and eGFR were considered continuous variables, and CKD stages were defined according to the KDIGO classification.
Non-normally distributed continuous variables were analyzed with the Mann–Whitney or Kruskal test, as appropriate. Categorical variables were analyzed with the chi-squared test. All statistical analyses were run in the MedCalc® statistical software, version 22.023 (MedCalc Software Ltd, Belgium; https://www.medcalc.org; 2024).
Results
Group 1
The CKD series of Group 1 consisted of 4,022 anonymous subjects, of which 1,421 (35.3%) were females and 2,601 (64.7%) were males; the median age was 61 years (IQR: 53–68 years; range: 20–74 years). Of these, 3,422 (85.1%) were in CKD stage 2, 478 (11.9%) in stage 3, 48 (1.2%) in stage 4, and 74 (1.8%) in stage 5. Median creatinine was 81.0 μmol/L (IQR: 72.0–93.0 μmol/L; range: 55.0–1,523.00 μmol/L), and median eGFR was 77.0 mL/min/1.73 m2 (IQR: 67.0–84.0 mL/min/1.73 m2; range: 3.0–89.0 mL/min/1.73 m2).
The control series of Group 1 consisted of 4,294 anonymous subjects. The distributions by sex, age, creatinine, and eGFR of the CKD series and the control series are reported in Table 1.
Table 1.
Clinical and biochemical data of anonymous subjects of the Group 1 CKD and control series. Data are presented as n (%) or as median (IQR).
| CKD series | Control series | |
|---|---|---|
| N | 4,022 | 4,294 |
| Sex | ||
| Females | 1,421 (35.3%) | 1,654 (38.5%) |
| Males | 2,601 (64.7%) | 2,640 (61.5%) |
| Median age (years) | 61 (53–68) | 49 (36–58) |
| Median creatinine (μmol/L) | 81.0 (72.0–93.0) | 64.0 (58.0–74.0) |
| Median eGFR (mL/min/1.73 m2) | 77.0 (67.0–84.0) | 100.0 (95.0–109.0) |
CKD, chronic kidney disease; eGFR, estimated glomerular filtration rate.
The median Ct of all Group 1 subjects was 1.00 ng/L (IQR: 1.00–2.90 ng/L; range: 1.00–99.6 ng/L). Median Ct levels were significantly higher in females (2.70 ng/L, IQR: 1.00–5.00 ng/L) than in males (1.00 ng/L, IQR: 1.00–1.30 ng/L) (P < 0.0001).
There was no statistically significant difference in median Ct levels between controls and the entire CKD series, the former being 1.00 ng/L (IQR: 1.00–2.90 ng/L; range: 1.00–99.40 ng/L) and the latter 1.00 ng/L (IQR: 1.00–2.80 ng/L; range: 1.00–99.60 ng/L) (P = 0.248).
In the CKD series, we found a significant association between Ct level and CKD stage. The median Ct levels by CKD stage were as follows: stage 2, 1.00 ng/L (IQR: 1.00–2.40 ng/L; range: 1.00–99.6 ng/L); stage 3, 1.20 ng/L (IQR: 1.00–4.30 ng/L; range: 1.00–91.90 ng/L); stage 4, 2.80 ng/L (IQR: 1.00–6.75 ng/L; range: 1.00–26.6 ng/L); and stage 5, 4.55 ng/L (IQR: 1.00–11.30 ng/L; range: 1.00–29.70 ng/L) (P < 0.001). Ct levels differed significantly between all stages, except for stages 4 and 5, which were not significantly different from each other. Median Ct was significantly lower in stage 2 than in the control series, while from stage 3 onward, it was significantly higher than in the controls (P < 0.001) (Fig. 2).
Figure 2.
Calcitonin (Ct) levels in Group 1 control series and CKD series by stage. NS, non-significant association (P > 0.05); CKD, chronic kidney disease.
We also found a significant difference in the distribution of Ct levels categorized as ≤10 ng/L or as >10 ng/L according to renal function, the most advanced CKD stages being significantly associated with Ct > 10 ng/L (P < 0.001) (Table 2).
Table 2.
Ct levels in Group 1 CKD complete series and by stage in comparison with controls with eGFR ≥ 90 mL/min/1.73 m2.
| Calcitonin | n | ||
|---|---|---|---|
| ≤10 ng/L | >10 ng/L | ||
| Controls | 4,110 (95.7%) | 184 (4.3%) | 4,294 |
| CKD series | 3,806 (94.6%) | 216 (5.4%) | 4,022 |
| Stage 2 | 3,278 (95.8%) | 144 (4.2%) | 3,422 |
| Stage 3 | 437 (91.4%) | 41 (8.6%) | 478 |
| Stage 4 | 40 (83.3%) | 8 (16.7%) | 48 |
| Stage 5 | 51 (68.9%) | 23 (31.1%) | 74 |
CKD, chronic kidney disease.
In the CKD series, Ct was ≤10 ng/L in 3,806 (94.6%) cases, >10 ng/L and ≤30 ng/L in 181 (4.5%) cases, and >30 ng/L and <100 ng/L in 35 (0.9%) cases, which means that 5.4% of these subjects had Ct values higher than 10 ng/L.
We found a positive correlation between Ct and creatinine levels (R2 = 0.014, y = 2.2095 + 0.008428x, P < 0.001) and a negative correlation between Ct and eGFR (R2 = 0.010, y = 5.9947–0.04071x, P < 0.0001) in CKD stages 2, 3, and 4, but no correlation in stage 5 (Fig. 3).
Figure 3.
Calcitonin (Ct) and creatinine levels in Group 1 CKD series with eGFR < 90 mL/min/1.73 m2.
Group 2
We enrolled 135 patients with CKD, 92 (68.1%) of which were males and 43 (31.9%) were females. The median age at enrollment was 74 years (IQR: 59.0–82.8 years; range: 25.0–93.0 years). Of these patients, 104 (77%) were undergoing dialysis treatment, while 31 (23%) had CKD that did not require this treatment. Other information, such as the patients’ smoking status, use of PPI, and anthropometric data, is reported in Table 3.
Table 3.
Anthropometric and clinical data of patients enrolled in Group 2 at the nephrology unit. Values are presented as n (%) or as median (IQR).
| Characteristics | Values |
|---|---|
| Sex | |
| Females | 43 (31.9%) |
| Males | 92 (68.1%) |
| Age (years) | 74.0 (59.0–82.8) |
| Weight (kg) | 74.5 (63.3–84.0) |
| BMI (kg/m2) | 25.4 (23.2–29.3) |
| PPI use | |
| Yes | 62 (45.9%) |
| No | 18 (13.3%) |
| Unknown | 55 (40.8%) |
| Dialysis treatment | |
| Yes | 104 (77.0%) |
| No | 31 (23.0%) |
| Smoking status | |
| Yes | 6 (4.4%) |
| No | 74 (54.8%) |
| Unknown | 55 (40.8%) |
PPI, proton pump inhibitor; IQR, interquartile range.
Seven (5.2%) patients had stage 2 CKD, 17 (12.6%) stage 3, five (3.7%) stage 4, and 106 (78.5%) stage 5. All but two of the 106 patients in stage 5 were undergoing dialysis treatment.
Median creatinine was 646.5 μmol/L (IQR: 160.0–868.5 μmol/L; range: 76.0–1,407.0 μmol/L), and median eGFR was 6.5 mL/min/1.73 m2 (IQR: 5.0–35.0 mL/min/1.73 m2; range: 3.0–88.0 mL/min/1.73 m2). The etiologies of renal disease in Group 2 patients are reported in Table 4.
Table 4.
Etiologies of renal disease in patients enrolled in Group 2.
| Etiology | Values, n (%) |
|---|---|
| Diabetic nephropathy | 32 (23.7%) |
| Glomerulonephritis | 19 (14.1%) |
| Iatrogenic | 13 (9.6%) |
| Hypertensive nephropathy | 12 (8.9%) |
| Polycystic renal disease | 12 (8.9%) |
| Obstructive | 7 (5.2%) |
| Miscellaneous | 40 (29.6%) |
There were no significant differences between the sexes in either creatinine levels or eGFR. The median levels and IQRs of calcium, phosphate, 25-OH vitamin D, and PTH were, respectively, 2.23 mmol/L (2.12–2.35 mmol/L), 1.36 mmol/L (1.08–1.65 mmol/L), 40.5 nmol/L (21.0–65.0 nmol/L), and 161.0 ng/L (74.0–281.5 ng/L).
The median Ct level was 3.7 ng/L (IQR: 1.0–7.0 ng/L; range: 1.0–24.2 ng/L).
There was a statistically significant difference between the sexes in median Ct levels, which were 1.00 ng/L (IQR: 1.00–3.98 ng/L; range: 1.0–19.8 ng/L) in females and 4.65 ng/L (IQR: 1.35–9.30 ng/L; range: 1.0–24.2 ng/L) in males (P < 0.001).
Ct levels were <1 ng/L in 35 (25.9%) patients, ≥1 ng/L and ≤10 ng/L in 75 (55.6%) patients, and >10 ng/L in 25 (18.5%). None of the patients had a Ct level >30 ng/L.
There was no statistically significant difference between the dialysis and non-dialysis patients in median Ct levels, which were 3.50 ng/L (IQR: 1.00–7.75 ng/L; range: 1.0–24.2 ng/L) in the former and 4.00 ng/L (IQR: 1.53–6.48 ng/L; range: 1.0–14.8 ng/L) in the latter.
Patients with Ct levels >10 ng/L for whom post-dialysis measurements were available exhibited higher median Ct values after dialysis than before, although the difference did not reach statistical significance (median pre-dialysis Ct: 12.2 ng/L (IQR: 11.3–21.6 ng/L; range: 10.4–21.8 ng/L); median post-dialysis Ct: 19.55 ng/L (IQR: 13.50–28.40 ng/L; range: 8.50–96.90 ng/L); P = 0.06).
There was no significant correlation between Ct and creatinine levels, nor between Ct and eGFR.
We found no statistically significant differences in Ct levels according to CKD stage: median Ct was 2.30 ng/L (IQR: 1.55–5.75 ng/L; range: 1.0–14.8 ng/L) in stage 2, 4.40 ng/L (IQR: 2.65–7.05 ng/L; range: 1.0–12.6 ng/L) in stage 3, 3.80 ng/L (IQR: 1.28–8.18 ng/L; range: 1.2–12.3 ng/L) in stage 4, and 3.50 ng/L (IQR: 1.00–7.70 ng/L; range: 1.0–24.2 ng/L) in stage 5 (P = 0.79).
Among patients with elevated Ct levels (>10 ng/L), we found no significant association between Ct level and CKD stage: Ct levels were >10 ng/L in 14.3% of patients in stage 2, 11.8% in stage 3, 20% in stage 4, and 19.8% in stage 5 (P = 0.87).
Repeat Ct measurements were taken for all 25 patients with Ct levels >10 ng/L, and elevated levels were confirmed in nine of them. These nine patients underwent thyroid ultrasound to rule out the presence of suspicious nodules: four had no nodules, while five had small nodules without features suggestive of malignancy. No signs of autoimmune thyroiditis were observed. Their Ct levels, dialysis treatment, and ultrasound findings are reported in Table 5.
Table 5.
Ct levels of patients with repeat measurements of Ct and ultrasound findings.
| Patient | Pre-dialysis Ct (ng/L) | Post-dialysis Ct (ng/L) | Ultrasound findings | Dialysis treatment |
|---|---|---|---|---|
| 1 | 12.3 | 12.0* | 14 mm nodule | No |
| 2 | 14.8 | 14.1* | No thyroid nodules | No |
| 3 | 12.6 | 10.9* | 4 mm nodule | No |
| 4 | 21.6 | 18.0 | 8 mm nodule | Yes |
| 5 | 21.8 | 31.3 | No thyroid nodules | Yes |
| 6 | 12.2 | 96.9 | 4 mm nodule | Yes |
| 7 | 11.3 | 21.1 | No thyroid nodules | Yes |
| 8 | 12.2 | 25.6 | No thyroid nodules | Yes |
| 9 | 10.4 | 16.1 | 11 mm nodule | Yes |
Repeated Ct measurements in patients without dialysis treatment.
We found no statistically significant associations between Ct and age, weight, BMI, smoking status, use of PPI, calcium, phosphate, PTH, or 25-OH vitamin D.
The median proCt level was 0.13 ng/mL (IQR: 0.04–0.42 ng/mL; range: 0.04–0.88 ng/mL); proCt was undetectable (<0.04 ng/mL) in 22 (34.9%) patients. Ct and proCt levels were not correlated (P = 0.087). Median proCt was higher in dialysis patients than in non-dialysis patients: 0.41 ng/mL (IQR: 0.26–0.55 ng/mL; range: 0.12–0.55 ng/mL) in the former; 0.04 ng/mL (IQR: 0.04–0.05 ng/mL; range: 0.04–0.14 ng/mL) in the latter (P < 0.001) (Fig. 4A).
Figure 4.
(A) Procalcitonin levels according to dialysis treatment in Group 2. (B) Procalcitonin levels according to CKD stage in Group 2. (C) Regression line of procalcitonin and creatinine levels in Group 2.
We found no significant differences in proCt levels between CKD stages 2, 3, and 4, but median proCt levels were significantly higher in stage 5 patients than in stage 2–4 patients, respectively, 0.39 ng/mL (IQR: 0.23–0.54 ng/mL; range: 0.05–0.88 ng/mL) and 0.04 ng/mL (IQR: 0.04–0.04 ng/mL; range: 0.04–0.04 ng/mL) (P < 0.001) (Fig. 4B). ProCt was detectable (≥0.04 ng/mL) in 24.1% of patients with CKD stages 2–4 and in 100% of stage 5 CKD patients, a statistically significant difference (P < 0.001). Finally, we found proCt values to be significantly related to creatinine levels (R2 = 0.44, y = 0.01875 + 0.0004280x, P < 0.001) and eGFR (R2 = 0.37, y = 0.4533–0.01110x, P < 0.001) (Fig. 4C).
Discussion
Calcitonin is a highly sensitive marker for MTC, but its low specificity is problematic, especially when it is only mildly elevated. The American Thyroid Association Guidelines for the management of MTC advise clinicians that misleadingly high Ct levels can occur with a variety of clinical diseases other than MTC, including chronic renal failure. With respect to the evaluation of Ct, CLIAs are confirmed as highly sensitive and specific for monomeric Ct (3).
CKD is one of the leading causes of death in this century. Approximately 850 million people worldwide are estimated to have kidney disease, which is reported to be the third fastest-growing cause of death globally (20, 21, 22). Given the high prevalence of CKD, accurate Ct measurement in this broad population of patients is crucial to avoid either unnecessary treatment or underestimating its clinical significance.
Since the initial observations on small series, subsequent studies have shown that Ct levels are elevated in patients with CKD (11, 12, 23, 24). In these studies, Ct was measured using RIA methods, mostly in patients being treated with chronic hemodialysis, and was reported to be higher than the normal range.
In a 1995 study on a small series of patients, Messa et al. found that subjects with normal renal function and CKD patients with eGFR > 30 mL/min/1.73 m2 had similar Ct levels, with a mean of approximately 10 ng/L in both groups. However, the mean Ct value was 34 ng/L in patients with eGFR < 30 mL/min/1.73 m2, measured by RIA (13). Our study corroborates previous findings that CKD patients with eGFR > 30 mL/min/1.73 m2 have, on the whole, similar Ct values to controls. Nevertheless, the median Ct values in our study were lower than those previously reported for both groups, possibly reflecting the better accuracy of the assessment method.
Approximately 30% of dialysis patients have been reported as having increased Ct values (15, 19, 25). More recently, Borchhardt et al. reported a median Ct value of 31 ng/L in a cohort of 17 patients with stage 4 and stage 5 CKD before kidney transplant, although measurement was made by CLIA in only a subset of cases. In a second study by the same group, the median Ct of 15 patients with CKD with C cell hyperplasia (CCH) was found to be as high as 35 ng/L (16, 17). It is only in recent years that studies have measured Ct levels in CKD patients using CLIA for the whole series (18, 19). Notably, Sabia et al. reported a median Ct of 8 ng/L in a cohort of 31 patients with dialysis-dependent CKD (18). Akan et al. reported a median Ct level of 8 ng/L in 283 dialysis patients, with no difference between pre- and post-dialysis measurements (19). In our study, Ct levels measured with accurate CLIA methods were higher than 10 ng/L in 5.4% of CKD patients as a whole. Looking at only those patients with end-stage renal disease (stage 5), median Ct was 4.55 ng/L (IQR: 1.00–11.30 ng/L) in the anonymous subjects dataset and 3.50 ng/L (IQR: 1.00–7.70 ng/L) in the clinical cohort. Ct was >10 ng/L in approximately 30% of the former group and 20% of the latter.
Our study substantially confirms previous observations that Ct can be expected to be higher than the normal range in 20–30% of patients in end-stage CKD, although the Ct levels in our study were substantially lower than those previously reported (15, 18, 19, 25). The difference between older findings and our own is likely to be mainly related to the assay used for measuring Ct, as two-site and two-step immunoassays are more accurate in recognizing mature Ct as distinct from Ct precursors, which are particularly abundant in the case of CKD (3, 9). Furthermore, the above-mentioned studies focused exclusively on end-stage renal disease and paid little attention to patients with moderately reduced GFR.
An apparent inconsistency in our results is that Ct levels were significantly associated with creatinine and eGFR among the anonymous subjects (Group 1), whereas the association was not significant in our smaller cluster of clinical CKD patients (Group 2). In our opinion, there are several reasons for this discrepancy. First, there were probably too few subjects in the Group 2 clinical cohort for the positive correlation between creatinine and Ct, and the negative correlation between eGFR and Ct, to reach statistical significance. The discrepancy could also be attributed to the different distributions of CKD stages in the two populations, as only 1.8% of the anonymous Group 1 subjects were in stage 5, against 78% of Group 2 CKD patients. We also found that in Group 1, the median Ct level increased from one CKD stage to the next up to stage 4, but stages 4 and 5 did not significantly differ from each other. The inconsistency is therefore only apparent, and the results are, after all, consistent if the different CKD stages in the two groups are taken into account. Moreover, since NET and chronic autoimmune gastritis were exclusion criteria for enrollment in Group 2, and PPI use and smoking were not significantly associated with Ct levels in this group, advanced-stage CKD may be considered an independent risk factor for increased Ct levels. However, as the anonymized data from Group 1 did not include information on comorbidities, the potential contribution of these conditions could not be evaluated on a larger scale.
One of the greatest strengths of our study is the very high number of patients – the largest so far reported in the literature in a clinical setting – which included not only subjects with very compromised renal function, but also a large number of patients at the less advanced CKD stages. Moreover, using a modern measurement method, the CLIA, across the entire cohort allowed us to accurately assess Ct levels.
Our study has some limitations. First, we were unable to correlate Ct levels with potential confounders in Group 1, such as comorbidities known to be associated with elevated Ct levels. Second, no definitive diagnostic conclusion, other than CKD, could be drawn for Group 2: patients with Ct levels above the reference range did not undergo fine-needle aspiration biopsy as no suspicious thyroid nodules were identified. In addition, the inclusion of two distinct populations with different distributions of CKD stages precluded direct comparison of the results of the two groups. Moreover, the exclusion of records with Ct levels >100 pg/mL may have resulted in an underestimation of the median Ct levels among the CKD patients in Group 1. Finally, because the laboratory records were anonymized, it was not possible to determine whether patients with MTC had also been included in the analysis.
However, the large number of records examined, the exclusion of patients with Ct levels >100 ng/L, and the rarity of MTC should mitigate this potential bias. A previous study by Fugazzola et al. used a baseline Ct cutoff of >30 pg/mL for females and >34 pg/mL for males to differentiate MTC from non-MTC patients (26). In our series, only 0.9% of the laboratory samples and none of the clinical cohort had Ct levels higher than 30 ng/L, so there is a very low probability that MTC patients were included in our dataset.
Finally, in a single study in which Ct was measured by both CLIA and RIA, Borchhardt et al. proposed a Ct cutoff of 50–150 ng/L to discriminate between MTC and CCH in patients with CKD and observed that 250 ng/L was the lowest Ct value among MTC patients on dialysis (17). In Group 2, Ct values for patients with CKD under dialysis treatment were below the reported cutoff for MTC diagnosis, further supporting the very low probability that MTC patients were included in our dataset.
In the clinical setting of Group 2 patients, we also evaluated proCt levels according to renal function and found them to be significantly related to creatinine and eGFR, with a significant difference between dialysis and non-dialysis patients. These findings, the opposite of those for Ct in the same population, were also confirmed by the absence of a correlation between Ct and proCt in our population. A study by Wu et al. found that serum concentrations of proCt were higher in patients with CKD than in healthy controls. Increased proCt has been related to a reduction in renal clearance and partly to a condition of low-grade chronic inflammation (27). Elevated Ct levels, on the other hand, have been reported as being secondary to CCH associated with CKD: the two different mechanisms potentially explain the different behaviors of the two markers according to dialysis and their reciprocal independence (13, 18). Interestingly, in our series, we did not find statistically significant differences in Ct levels according to chronic dialysis treatment, which may be explained by the high number of dialysis patients (77%) in our clinical population of CKD patients. The correlation between Ct and creatinine that was observed in the anonymous records was not confirmed in CKD stage 5, which may be related to the fact that elevated Ct in end-stage renal disease is not related to reduced filtration, but rather is secondary to increased C cell hormone secretion (13, 18). Consequently, the observed increase in Ct after dialysis, although not statistically significant, may be secondary to a reduction in circulating blood volume induced by dialysis.
Our results suggest that proCt is not a suitable complementary marker for the diagnosis of MTC in patients with CKD, particularly in those requiring dialysis. We recently asserted that the combined use of Ct and proCt may improve diagnostic accuracy in patients with mildly elevated Ct levels, using a proCt cutoff of 0.04 ng/mL (28). However, this finding does not apply to the CKD population examined in the present study, where proCt levels of all patients with stage 5 CKD and 24% of those in earlier stages were ≥0.04 ng/mL. This means that the use of proCt as a complementary diagnostic marker for MTC in this setting may lead to significant overtreatment. Although we have no definitive confirmation of the presence or absence of MTC in our series, we believe that proCt may be more of a confounding factor than a reliable diagnostic tool in CKD patients, particularly in advanced renal disease, where chronic inflammation may contribute to persistently elevated proCt levels.
Secondary hypercalcitoninemia is an important issue, and current guidelines state that serum Ct levels may be elevated in different thyroid- and non-thyroid-related conditions, such as CKD (3). Our group recently found no increase in Ct levels, measured by CLIA, in patients with chronic autoimmune gastritis, regardless of the presence of autoimmune thyroiditis (7). In the present study, we confirmed that Ct levels may be elevated in CKD patients, although the median Ct lies within the normal range in all stages of CKD.
Conclusion
The present study confirms that Ct levels increase in patients with CKD, continuing to rise with advancing CKD stage, and in significant relation to creatinine and eGFR. However, overall, we found that median Ct lies within the normal range in all stages of CKD and is only slightly higher in CKD patients than in controls. Ct is significantly elevated for clinical practice only from stage 4 and is higher than the normal range in approximately 30% of stage 5 CKD cases, although absolute Ct levels measured by CLIA are often only slightly above the normal range. The use of proCt in patients with CKD warrants careful consideration, as it may potentially lead to overtreatment in cases of mildly elevated Ct levels.
Declaration of interest
The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding
This research did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.
Author contribution statement
IP: original draft (lead), writing – review (lead), editing (equal). SC: original draft (equal), writing – review (equal), editing (equal). LF, CC, FB, FC, FKM, and LFS: writing – review and editing (supporting), data collection (supporting). MM: writing – review and editing (supporting), methodology (supporting). FN: writing – review and editing (supporting), methodology (supporting). CM: original draft (equal), writing – review (equal), editing (lead), methodology (lead).
Acknowledgment
The authors thank Dr Tessa Say for text editing and Dr Diego Faggian for his valuable support in the measurement of calcitonin levels.
References
- 1.Verbeek HHG, de Groot JWB, Sluiter WJ, et al. Calcitonin testing for detection of medullary thyroid cancer in people with thyroid nodules. Cochrane Database Syst Rev 2020. 3 CD010159. ( 10.1002/14651858.CD010159.pub2) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Costante G, Meringolo D, Durante C, et al. Predictive value of serum calcitonin levels for preoperative diagnosis of medullary thyroid carcinoma in a cohort of 5817 consecutive patients with thyroid nodules. J Clin Endocrinol Metab 2007. 92 450–455. ( 10.1210/jc.2006-1590) [DOI] [PubMed] [Google Scholar]
- 3.Wells SA, Asa SL, Dralle H, et al. Revised American Thyroid Association Guidelines for the management of medullary thyroid carcinoma. Thyroid 2015. 25 567–610. ( 10.1089/thy.2014.0335) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Toledo SPA, Lourenço DM, Santos MA, et al. Hypercalcitoninemia is not pathognomonic of medullary thyroid carcinoma. Clinics 2009. 64 699–706. ( 10.1590/s1807-59322009000700015) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.d’Herbomez M, Caron P, Bauters C, et al. Reference range of serum calcitonin levels in humans: influence of calcitonin assays, sex, age, and cigarette smoking. Eur J Endocrinol 2007. 157 749–755. ( 10.1530/eje-07-0566) [DOI] [PubMed] [Google Scholar]
- 6.Grani G, Nesca A, Del Sordo M, et al. Interpretation of serum calcitonin in patients with chronic autoimmune thyroiditis. Endocr Relat Cancer 2012. 19 345–349. ( 10.1530/erc-12-0013) [DOI] [PubMed] [Google Scholar]
- 7.Censi S, Carducci S, Zoppini G, et al. Calcitonin levels in autoimmune atrophic gastritis-related hypergastrinemia. J Endocrinological Invest 2024. 47 357–365. ( 10.1007/s40618-023-02152-x) [DOI] [PubMed] [Google Scholar]
- 8.Ito Y, Kaneko H, Sasaki Y, et al. Calcitonin levels by ECLIA correlate well with RIA values in higher range but are affected by sex, TgAb, and renal function in lower range. Endocr J 2020. 67 759–770. ( 10.1507/endocrj.ej19-0610) [DOI] [PubMed] [Google Scholar]
- 9.Censi S, Cavedon E, Fernando SW, et al. Calcitonin measurement and immunoassay interference: a case report and literature review. Clin Chem Lab Med 2016. 54 1861–1870. ( 10.1515/cclm-2015-1161) [DOI] [PubMed] [Google Scholar]
- 10.Alves TG, Kasamatsu TS, Yang JH, et al. Macrocalcitonin is a novel pitfall in the routine of serum calcitonin immunoassay. J Clin Endocrinol Metab 2016. 101 653–658. ( 10.1210/jc.2015-3137) [DOI] [PubMed] [Google Scholar]
- 11.Nielsen HE, Christensen CK & Olsen KJ. Serum calcitonin in patients with chronic renal disease. Acta Med Scand 1979. 205 615–618. ( 10.1111/j.0954-6820.1979.tb06114.x) [DOI] [PubMed] [Google Scholar]
- 12.Escalada J, Teruel L, Pav I, et al. Normal calcitonin response to pentagastrin stimulation in patients with chronic renal failure. Acta Endocrinol 1993. 129 39–41. ( 10.1530/acta.0.1290039) [DOI] [PubMed] [Google Scholar]
- 13.Messa P, Mioni G, Turrin D, et al. The calcitonin-calcium relation curve and calcitonin secretory parameters in renal patients with variable degrees of renal function. Nephrol Dial Transplant 1995. 10 2259–2265. ( 10.1093/ndt/10.12.2259) [DOI] [PubMed] [Google Scholar]
- 14.Lissak B, Baudin E, Cohen R, et al. Pentagastrin testing in patients with renal insufficiency: normal responsivity of mature calcitonin. Thyroid 1998. 8 265–268. ( 10.1089/thy.1998.8.265) [DOI] [PubMed] [Google Scholar]
- 15.Kotzmann H, Schmidt A, Scheuba C, et al. Basal calcitonin levels and the response to pentagastrin stimulation in patients after kidney transplantation or on chronic hemodialysis as indicators of medullary carcinoma. Thyroid 1999. 9 943–947. ( 10.1089/thy.1999.9.943) [DOI] [PubMed] [Google Scholar]
- 16.Borchhardt KA, Hörl WH & Sunder-Plassmann G. Reversibility of “secondary hypercalcitoninemia” after kidney transplantation. Am J Transplant 2005. 5 1757–1763. ( 10.1111/j.1600-6143.2005.00908.x) [DOI] [PubMed] [Google Scholar]
- 17.Borchhardt KA, Heinzl H, Gessl A, et al. Calcitonin concentrations in patients with chronic kidney disease and medullary thyroid carcinoma or c-cell hyperplasia. Kidney Int 2006. 70 2014–2020. ( 10.1038/sj.ki.5001888) [DOI] [PubMed] [Google Scholar]
- 18.Sabia R, Wagner M, Susa K, et al. Calcitonin concentrations in patients with chronic kidney disease on hemodialysis in reference to parathyroidectomy. BMC Res Notes 2019. 12 439. ( 10.1186/s13104-019-4479-6) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Akan B, Böhmig G, Sunder-Plassmann G, et al. Prevalence of hypercalcitoninemia in patients on maintenance dialysis referred to kidney transplantation. Clin Nephrol 2009. 71 538–542. ( 10.5414/cnp71538) [DOI] [PubMed] [Google Scholar]
- 20.Stevens PE, Ahmed SB, Carrero JJ, et al. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int 2024. 105 S117–S314. ( 10.1016/j.kint.2023.10.018) [DOI] [PubMed] [Google Scholar]
- 21.Jager KJ, Kovesdy C, Langham R, et al. A single number for advocacy and communication – worldwide more than 850 million individuals have kidney diseases. Kidney Int 2019. 96 1048–1050. ( 10.1016/j.kint.2019.07.012) [DOI] [PubMed] [Google Scholar]
- 22.Francis A, Harhay MN, Ong ACM, et al. Chronic kidney disease and the global public health agenda: an international consensus. Nat Rev Nephrol 2024. 20 473–485. ( 10.1038/s41581-024-00820-6) [DOI] [PubMed] [Google Scholar]
- 23.Nielsen HE & Olsen KJ. Serum calcitonin after renal transplantation. Acta Med Scand 1979. 205 619–621. ( 10.1111/j.0954-6820.1979.tb06115.x) [DOI] [PubMed] [Google Scholar]
- 24.Mulder H, Silberbusch J, Hackeng WH, et al. Enhanced calcitonin release in chronic renal failure depending on the absence of severe secondary hyperparathyroidism. Nephron 1982. 31 123–128. ( 10.1159/000182630) [DOI] [PubMed] [Google Scholar]
- 25.Niccoli P, Brunet P, Roubicek C, et al. Abnormal calcitonin basal levels and pentagastrin response in patients with chronic renal failure on maintenance hemodialysis. Eur J Endocrinol 1995. 132 75–81. ( 10.1530/eje.0.1320075) [DOI] [PubMed] [Google Scholar]
- 26.Fugazzola L, Di Stefano M, Censi S, et al. Basal and stimulated calcitonin for the diagnosis of medullary thyroid cancer: updated thresholds and safety assessment. J Endocrinological Invest 2021. 44 587–597. ( 10.1007/s40618-020-01356-9) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Wu SC, Liang CX, Zhang YL, et al. Elevated serum procalcitonin level in patients with chronic kidney disease without infection: a case-control study. J Clin Lab Anal 2020. 34 e23065. ( 10.1002/jcla.23065) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Clausi C, Censi S, Zanin E, et al. Combining procalcitonin and calcitonin for the diagnosis of medullary thyroid cancer: a two-step approach. Clin Endocrinol 2025. 103 587–595. ( 10.1111/cen.15287) [DOI] [PMC free article] [PubMed] [Google Scholar]