Random Blood Glucose: A Robust Risk Factor For Type 2 Diabetes

Abstract

Context:

Although random blood glucose (RBG) values are common in clinical practice, the role of elevated RBG values as a risk factor for type 2 diabetes is not well described.

Objective:

This study aimed to examine nondiagnostic, RBG values as a risk factor for type 2 diabetes

Design:

This was a cross-sectional study of National Health and Nutrition Examination Surveys (NHANES) participants (2005–2010).

Participants:

Nonfasting NHANES participants (n = 13 792) without diagnosed diabetes were included.

Primary Outcome:

The primary outcome was glycemic status (normal glycemia, undiagnosed prediabetes, or undiagnosed diabetes) using hemoglobin HbA_1C as the criterion standard.

Analysis:

Multinomial logistic regression examined associations between diabetes risk factors and RBG values according to glycemic status. Associations between current U.S. screening strategies and a hypothetical RBG screening strategy with undiagnosed diabetes were examined.

Results:

In unadjusted analyses, a single RBG ≥ 100 mg/dL (5.6 mmol/L) was more strongly associated with undiagnosed diabetes than any single risk factor (odds ratio [OR], 31.2; 95% confidence interval [CI], 21.3–45.5) and remained strongly associated with undiagnosed diabetes (OR, 20.4; 95% CI, 14.0–29.6) after adjustment for traditional diabetes risk factors. Using RBG < 100 mg/dL as a reference, the adjusted odds of undiagnosed diabetes increased significantly as RBG increased. RBG 100–119 mg/dL (OR 7.1; 95% CI 4.4–11.4); RBG 120–139 mg/dL (OR 30.3; 95% CI 20.0–46.0); RBG ≥ 140 mg/dL (OR 256; 95% CI 150.0–436.9). As a hypothetical screening strategy, an elevated RBG was more strongly associated with undiagnosed diabetes than current United States Preventative Services Task Force guidelines (hypertension alone; P < .0001) and similar to American Diabetes Association guidelines (P = .12).

Conclusions:

A single RBG ≥ 100 mg/dL is more strongly associated with undiagnosed diabetes than traditional risk factors. Abnormal RBG values are a risk factor for diabetes and should be considered in screening guidelines.

Type 2 diabetes is a significant and costly public health epidemic that is projected to affect one in three U.S. adults by 2050 (1). This projected increase is driven largely by the 86 million Americans with prediabetes, which, if unrecognized and untreated will likely progress to frank diabetes (2, 3). Despite well-established diabetes screening guidelines (4, 5), greater than 8 million people with diabetes and 80 million people with prediabetes remain undiagnosed or unaware of their condition (2, 6).

Current U.S. diabetes screening guidelines recommend targeted screening of high-risk individuals; however, guidelines define diabetes risk differently. The United States Preventative Services Task Force (USPSTF) guideline recommends screening only when an individual has a sustained elevation in blood pressure (treated or untreated) greater than 135/80 mm Hg (5). In contrast, the multifactorial American Diabetes Association (ADA) guideline (4) recommends screening for all individuals age 45 years and older and individuals at any age if their body mass index (BMI) is at least 25 kg/m² and they have one additional risk factor including: nonwhite race, family history of diabetes, hypertension, dyslipidemia, history of cardiovascular disease, physical inactivity, polycystic ovarian syndrome, history of gestational diabetes, delivery of an infant weighing greater than 9 pounds, or other clinical conditions associated with insulin resistance. Screening is also recommended for individuals with prediabetes when glycated hemoglobin (HbA_1C) values, fasting glucose values, and 2-hour glucose values obtained via an oral glucose tolerance test are abnormal but fail to reach diagnostic thresholds (4). The International Diabetes Federation guidelines extend these recommendations even further to recommend screening for individuals with random, nondiagnostic glucose values between 100 and 199 mg/dL (5.6–11.0 mmol/L), although the evidence supporting this recommendation is limited (7). Random blood glucose values are not included as a risk factor in U.S. screening recommendations.

To improve screening strategies and identification of individuals with undiagnosed diabetes and prediabetes, greater understanding of the risk factors for undiagnosed diabetes and prediabetes are needed. This study seeks to: 1) describe the prevalence diabetes risk factors in individuals with undiagnosed diabetes and prediabetes; 2) examine the association between random glucose values and undiagnosed diabetes and prediabetes; and 3) explore the associations between ADA screening guidelines, USPSTF screening guidelines, and a hypothetical random glucose screening strategy with undiagnosed disease.

Research design and methods

We analyzed merged data from the 2005–2010 National Health and Nutrition Examination Surveys (NHANES). NHANES is a repeated, cross-sectional, stratified survey designed to be representative of the noninstitutionalized U.S. population using a multistage probability sample. Participants complete an in-home interview for basic demographic and health information along with a scheduled visit to a mobile examination center for physical examination and laboratory testing (8). All participants gave written informed consent and the research ethics boards of the National Center for Health Statistics approved all protocols.

Study population

The study population consisted of nonpregnant adults age 18 years and older who completed both the NHANES interview and mobile exam center examination between 2005 and 2010. We excluded participants with diagnosed diabetes or prediabetes. Participants responding “yes” when asked “Other than during pregnancy, have you ever been told by a doctor or health professional that you have diabetes or sugar diabetes?” were considered to have diabetes and excluded from the analytic sample. Participants responding “yes” to the question: “Have you ever been told by a doctor or other health professional that you have any of the following: prediabetes, impaired fasting glucose, impaired glucose tolerance, borderline diabetes, or that your blood glucose is higher than normal but not high enough to be called diabetes or sugar diabetes?” were also excluded. Participants examined in a nonfasting state who had both hemoglobin HbA_1C and random serum blood glucose (RBG) test results were included in analysis.

Measures

Patient characteristics and diabetes risk factors including age, race, family history of diabetes, and family history of cardiovascular disease were obtained from questionnaire data. BMI was calculated from measured height and weight and classified as normal weight (BMI < 25 kg/m²); overweight (BMI 25–30 kg/m²); or obese (BMI ≥ 30 kg/m²). Participants self-reporting hypertension or high cholesterol diagnosed by a physician or other health professional were considered to have hypertension and high cholesterol. Polycystic ovary syndrome, acanthosis nigricans, and other clinical conditions associated with insulin resistance were not included as a risk factor for diabetes because we were unable to identify these participants within NHANES. Gestational diabetes and delivery of an infant weighing greater than 9 pounds were not included as risk factors because data were not available in 2005–2006 NHANES. Participants meeting age, BMI, family history, race, hypertension, high cholesterol, or cardiovascular disease criteria were considered to satisfy the ADA screening guideline. We subsequently classified patients using the ADA (4) and USPSTF (5) screening guidelines by whether screening was indicated (yes/no). All questionnaire and examination components utilized in analysis were identical across the three survey cycles used.

Serum RBG measurements were determined using the Beckman Oxygen electrode, glucose oxidase method. Between 2007 and 2012, one instrument change occurred [Beckman Synchron LX20 (2007) to the Beckman Unicel CxC800 Synchron (2008–2012)] (Beckman Coulter). All measurements were performed by Collaborative Laboratory Services, LLC (9).

HbA_1C assays were conducted using HPLC methods on instruments certified by the National Glycohemoglobin Standardization Program (9). All HbA_1C results were subsequently standardized to the Diabetes Control and Complications Trial reference standard (10). Between 2007 and 2010, all HbA_1C assays were performed at a single laboratory site (Minneapolis, MN). The instrument used to analyze HbA_1C changed from the Tosoh HbA_1C 2.2 Plus (2005–2007) to the Tosoh HbA_1C G7 (2007–2010). Despite this, HbA_1C values were analyzed without corrections as recommended by the National Center for Health Statistics (11).

We defined diabetes, prediabetes, and dysglycemia using HbA_1C as the criterion standard. Diabetes was defined as having an HbA_1C ≥ 6.5% (48 mmol/mol) and prediabetes as having an HbA_1C 5.7–6.4% (39–46 mmol/mol). Dysglycemia was defined as having an HbA_1C at least 5.7% (39 mmol/mol). Fasting glucose was not included in our diabetes definition because individuals examined in a fasting state did not have an RBG value available.

Statistical analysis

We calculated means and percentages of participant characteristics by glycemic status and compared values across groups using Rao-Scott χ² tests for categorical variables and F tests for continuous variables. We used multinomial logistic regression to examine associations between risk factors and undiagnosed diabetes and prediabetes. We further aggregated risk factors according to ADA (4) and USPSTF (5) diabetes screening guidelines to examine associations between these screening strategies and undiagnosed diabetes and prediabetes. We also examined unadjusted and covariate-adjusted associations between a single RBG at least 100 mg/dL (5.6 mmol/L) with undiagnosed diabetes and prediabetes. Models were adjusted for traditional diabetes risk factors including age, sex, race, BMI, hypertension, hyperlipidemia, cardiovascular disease, and family history of diabetes. The odds ratio (OR) of detecting undiagnosed diabetes and prediabetes using ADA, USPSTF, and RBG screening strategies were compared using Wald tests. Analyses were conducted in SAS version 9.3 (SAS Institute Inc) and Stata/SE version 13.1 (StataCorp LP) using survey procedures to account for sampling weights. Appropriate sampling weights were applied to account for unequal selection probabilities and nonresponse such that estimates are representative of the U.S. noninstitutionalized civilian population (8). P < .05 was considered statistically significant. This study was approved by the institutional review board at the University of Texas Southwestern Medical Center at Dallas.

Results

A total of 13 792 participants met eligibility criteria. Among all participants age at least 18 years without diagnosed diabetes, 1.9% had undiagnosed diabetes and 20.2% had undiagnosed prediabetes by HbA_1C criteria. Participant characteristics by glycemic status are shown in Table 1. Overall, the prevalence of traditional diabetes risk factors is increased in individuals with undiagnosed prediabetes and diabetes. The prevalence of older age, nonwhite race, positive family history of diabetes, increasing BMI, and a diagnosis of hypertension, hyperlipidemia, and cardiovascular disease increases across the spectrum of dysglycemia from normal to prediabetes, to diabetes, with the highest prevalence of risk factors present in individuals with undiagnosed diabetes (Table 1). Men were more likely than women to have undiagnosed diabetes.

Table 1.

Participant Demographics and Risk Factors by Glycemic Status

Characteristic	No Diabetes	Undiagnosed Prediabetes	Undiagnosed Diabetes	P Value
Mean age, y	41.7 (0.3)	55.4 (0.4)	58.6 (0.9)	<.001
Female	50.8 (0.5)	51.7 (1.1)	41.3 (3.0)	.009
Race
Non-Hispanic white	72.9 (1.8)	65.0 (0.9)	57.0 (5.2)	<.001
Non-Hispanic Black	8.8 (0.8)	15.6 (0.6)	17.0 (2.4)	<.001
Mexican American	8.3 (0.9)	8.4 (0.4)	14.0 (2.5)	.005
Other Hispanic	4.3 (0.6)	4.5 (0.3)	4.8 (1.0)	.83
Other race	5.7 (0.5)	6.5 (0.6)	7.3 (2.7)	.48
Education <12 y	15.3 (0.8)	24.2 (0.9)	29.6 (2.7)	<.001
Married	53.7 (1.0)	58.1 (1.1)	56.0 (3.2)	<.001
Uninsured	21.4 (0.9)	18.5 (0.8)	22.8 (3.3)	.012
Family history diabetes	30.9 (0.6)	40.0 (1.1)	46.1 (2.7)	<.001
Mean BMI, kg/m2	27.3 (0.1)	30.2 (0.1)	34.2 (0.5)	<.001
Hypertension	20.6 (0.7)	40.5 (1.1)	49.6 (2.8)	<.001
Hyperlipidemia	22.1 (0.7)	39.0 (1.1)	37.1 (3.2)	<.001
Cardiovascular disease	3.8 (0.3)	9.6 (0.6)	14.8 (1.6)	<.001
No doctor visit past 12 mo	19.1 (0.5)	13.8 (0.7)	21.0 (2.8)	<.001
Screened for diabetes past 3 y	35.9 (0.5)	49.6 (1.1)	56.1 (2.8)	<.001
Mean random blood glucose, mg/dL	89.9 (0.2)	99.1 (0.4)	156.0 (5.3)	<.001
Mean HbA1C, %	5.2 (0.01)	5.9 (0.01)	7.6 (0.1)	<.001
Mean HbA1C, mmol/mol	33 (0.1)	41 (0.1)	60 (1.1)	<.001

Data presented as percent (se) unless otherwise noted. All estimates are weighted to U.S. population estimates. Random glucose (mg/dL) × 0.5551 = mmol/L.

Although those with undiagnosed diabetes and prediabetes were more likely to be screened in the past 3 years compared with those with normoglycemia, only slightly more than half of those with undiagnosed diabetes (56.1%) and half (49.6%) of those with undiagnosed prediabetes reported having been screened for diabetes in the past 3 years. However, this does not seem to be for lack of physician visits because only 21.0% and 13.8% of patients with undiagnosed diabetes and prediabetes respectively did not have a doctor's visit in the past 12 months.

The mean HbA_1C increased across the glycemic spectrum: no diabetes HbA_1C = 5.2% (33 mmol/mol); undiagnosed prediabetes HbA_1C = 5.9% (41 mmol/mol); and undiagnosed diabetes HbA_1C = 7.6% (60 mmol/mol) (Table 1). Translating these HbA_1C values into estimated average glucose values during the preceding 3 months (12), participants with no diabetes had an estimated average glucose of 103 mg/dL (5.7 mmol/L) compared with 123 mg/dL (6.8 mmol/L) and 171 mg/dL (9.5 mmol/L) in participants with undiagnosed prediabetes and diabetes, respectively. The mean value of a single RBG measure across groups increased from 89.9 mg/dL (5.0 mmol/L) in patients with no diabetes, to 99.1 mg/dL (5.5 mmol/L) in patients with undiagnosed prediabetes, to 156.0 mg/dL (8.7 mmol/L) in patients with undiagnosed diabetes.

In univariate analyses, the risk factors most strongly associated with undiagnosed diabetes were a single RBG at least 100 mg/dL (5.6 mmol/L) (OR, 31.2; 95% confidence interval [CI], 21.3–45.5), BMI at least 25 kg/m² (OR, 10.9 95% CI, 6.8–17.5), and age at least 45 years (OR, 7.9; 95% CI, 5.7–10.9). Comorbid disease risk factors such as a history of cardiovascular disease, hypertension, or hyperlipidemia were more modestly associated with dysglycemia (Table 2). As a single risk factor, race and family history demonstrated the weakest associations with undiagnosed diabetes.

Table 2.

Univariate Associations between Risk Factors and Undiagnosed Prediabetes, Diabetes, and Dysglycemia (Prediabetes + Diabetes)

Characteristic	OR (95% CI)
	Undiagnosed Prediabetes	Undiagnosed Diabetes	Dysglycemia
Age ≥ 45 y	4.8 (4.2–5.4)	7.9 (5.7–10.9)	4.9 (4.4–5.6)
BMI ≥ 25 kg/m2	2.3 (2.0–2.6)	10.9 (6.8–17.5)	2.5 (2.2–2.8)
Non-white race	1.4 (1.3–1.7)	2.0 (1.4–2.9)	1.5 (1.3–1.7)
Family history of diabetes	1.5 (1.4–1.6)	1.9 (1.5–2.4)	1.5 (1.4–1.7)
Hypertension	2.6 (2.4–2.9)	3.8 (2.9–5.0)	2.7 (2.5–3.0)
Hyperlipidemia	2.3 (2.0–2.6)	2.1 (1.6–2.8)	2.3 (2.0–2.6)
Cardiovascular disease	2.7 (2.2–3.3)	4.5 (3.4–5.9)	2.9 (2.4–3.4)
Random Glucose ≥ 100 mg/dL	3.3 (3.0–3.8)	31.2 (21.3–45.5)	3.9 (3.5–4.4)

Weighted SEs used to compute CIs. Random glucose (mg/dL) × 0.5551 = mmol/L.

Age at least 45 years was the risk factor most strongly associated with undiagnosed prediabetes (OR, 4.8; 95% CI, 4.2–5.4) and undiagnosed dysglycemia (OR, 4.9; 95% CI, 4.4–5.6). A single RBG at least 100 mg/dL (5.6 mmol/L) was more strongly associated with undiagnosed prediabetes (OR, 3.3; 95% CI, 3.0–3.8) and undiagnosed dysglycemia (OR, 3.9; 95% CI, 3.5–4.4) than all other risk factors examined except for age (Table 2).

Table 3 shows a strong dose-response relationship between increasing RBG values and higher risk-adjusted odds of undiagnosed prediabetes, undiagnosed diabetes, and overall dysglycemia. For individuals with a single RBG 100–119 mg/dL (5.6–6.6 mmol/L), the odds of undiagnosed diabetes were 7.1; 95% CI, 4.4–11.4. For glucose values 120–139 mg/dL (6.7–7.7 mmol/L) and at least 140 mg/dL (7.8 mmol/L), the odds of undiagnosed diabetes were 30.3; 95% CI, 20.0–46.0 and 256; 95% CI, 150.0–436.9, respectively.

Table 3.

Dose Response Relationship between Random Blood Glucose (RBG) and Undiagnosed Diabetes, Prediabetes, and Dysglycemia (Prediabetes + Diabetes)

Glucose Range	Adjusted Odds Ratio (95% CI)
	Undiagnosed Prediabetes	Undiagnosed Diabetes	Dysglycemia
RBG < 100 mg/dL	Reference	Reference	Reference
RBG 100–119 mg/dL	2.2 (1.9–2.5)	7.1 (4.4–11.4)	2.3 (2.0–2.7)
RBG 120–139 mg/dL	3.3 (2.6–4.2)	30.3 (20.0–46.0)	3.8 (3.0–4.9)
RBG ≥ 140 mg/dL	3.5 (2.2–5.5)	256.0 (150.0–436.9)	8.4 (5.7–12.3)

All values adjusted for age, sex, race, BMI, hypertension, hyperlipidemia, cardiovascular disease, and family history of diabetes. Random glucose (mg/dL) × 0.5551 = mmol/L.

In multivariate models, a single RBG at least 100 mg/dL (5.6 mmol/L) was associated with a 20-fold increased risk of undiagnosed diabetes (OR, 20.4; 95% CI, 14.0–29.6) and over double the odds of undiagnosed prediabetes (OR, 2.4; 95% CI, 2.1–2.7) even after adjusting for age, sex, race, BMI, hypertension, hyperlipidemia, cardiovascular disease, and family history of diabetes. Overall, a single RBG at least 100 mg/dL (5.6 mmol/L) nearly tripled the risk-adjusted odds of undiagnosed dysglycemia (OR, 2.8; 95% CI, 2.5–3.2) (Table 4).

Table 4.

Odds of Having Undiagnosed Diabetes, Prediabetes, or Dysglycemia (Prediabetes + Diabetes) According to Different Screening Strategies

Screening Strategy	Odds Ratio (95% CI)
	Undiagnosed Prediabetes	Undiagnosed Diabetes	Dysglycemia
USPSTF Guidelinesa	2.6 (2.4–2.9)	3.8 (2.9–5.0)	2.7 (2.5–3.0)
ADA Guidelinesb	9.8 (8.1–11.8)	50.6 (17.7–144.5)	10.6 (8.8–12.7)
Random Glucose ≥ 100 mg/dLc	2.4 (2.1–2.7)	20.4 (14.0–29.6)	2.8 (2.5–3.2)

All results presented as weighted odds ratios. Random glucose (mg/dL) × 0.5551 = mmol/L.

^aUSPSTF Guideline: diagnosed hypertension

^bADA Guideline: All individuals age ≥ 45 y or those with BMI ≥ 25 kg/m² and family history of diabetes, nonwhite race, hypertension, high cholesterol, cardiovascular disease.

^cAdjusted for age, sex, race, BMI, hypertension, hyperlipidemia, cardiovascular disease, and family history of diabetes.

As shown in Table 4, patients meeting USPSTF and ADA screening guidelines had increased odds of having undiagnosed prediabetes and undiagnosed diabetes. Meeting the single-factor USPSTF guideline criteria (presence of hypertension alone) nearly tripled the odds of prediabetes (OR, 2.6; 95% CI, 2.4–2.9) and dysglycemia (OR, 2.7; 95% CI, 2.5–3.0) and increased the odds of diabetes nearly 4-fold (OR, 3.8; 95% CI, 2.9–5.0). Individuals meeting the multirisk factor ADA guidelines had approximately a 10-fold increase in the odds of prediabetes (OR, 9.8; 95% CI, 8.1–11.8) and dysglycemia (OR, 10.6; 95% CI, 8.8–12.7). Meeting ADA guidelines increased the odds of diabetes by over 50-fold (OR, 50.6; 95% CI, 17.7–144.5).

A screening strategy based on a single RBG at least 100 mg/dL (5.6 mmol/L) (OR, 20.4; 95% CI, 14.0–29.6) was much more strongly associated with undiagnosed diabetes than USPSTF guidelines (P < .0001) and not statistically different from the ADA screening guideline (P = .12). For detecting undiagnosed prediabetes, the single RBG strategy was similar to the USPSTF guideline (P = .32) but not as predictive as the ADA screening strategy (P < .0001).

Conclusions

In a nationally representative sample of the U.S. population without diagnosed diabetes, a single RBG at least 100 mg/dL (5.6 mmol/L) is strongly associated with undiagnosed diabetes and demonstrates a robust dose response. In fact, a RBG at least 100 mg/dL (5.6 mmol/L) was the single strongest predictor of undiagnosed diabetes outperforming all other traditional risk factors. As a simple strategy to detect undiagnosed diabetes, the association with undiagnosed disease for a single RBG at least 100 mg/dL (5.6 mmol/L) is stronger than the USPSTF diabetes screening guidelines, which recommend screening based on the presence of hypertension alone (5), and similar to the multirisk factor, more complex ADA screening guidelines (4). Nondiagnostic, random glucose values should be considered in diabetes risk assessments and may improve detection of undiagnosed cases of diabetes and prediabetes.

Among individuals with undiagnosed prediabetes and diabetes, traditional diabetes risk factors are common. In general, the prevalence of individual risk factors increases across the glycemic spectrum from no diabetes, to undiagnosed prediabetes and undiagnosed diabetes. Similar to other studies (13–17), we observed significant associations between age, BMI, hypertension, family history, and undiagnosed disease. Although we found race and family history to be significant risk factors, their association with undiagnosed disease was more modest than other risk factors. Similar to a recent study finding that men have a higher prevalence of diagnosed diabetes than women (18), we found that men were also more likely to have undiagnosed diabetes.

Although the vast majority of individuals with undiagnosed diabetes and prediabetes are insured and have visited a healthcare provider in the past 12 months, similar to other studies (19), we found that only half of eligible individuals reported being screened diabetes in the past 3 years. Given the burden of undiagnosed disease and the prevalence of diabetes risk factors, missed opportunities for diabetes screening are common (15). Although the barriers to diabetes screening in clinical practice are poorly understood, the assessment of diabetes risk factors and ordering of diabetes screening is largely at the discretion of individual clinicians and may be an afterthought in time-constrained clinic visits. Automated risk assessment and clinical decision support can facilitate provider workflow and be effective tools to increase screening rates for cancer (20). However, automation and implementation of multifactorial diabetes screening guidelines in clinical practice is challenging and parsimonious risk assessment models are needed (21).

The development of automated risk models capable of informing clinical decision support requires accurate data that are readily available. Identification and abstraction of traditional diabetes risk factors from electronic medical records is largely dependent on the data entry and coding of end users. However, laboratory data are readily available and electronically integrated into most electronic medical records. As such, both historic and prospective RBG values collected in routine clinical practice could provide a platform to develop automated diabetes risk assessment. Although prediabetes is a strong risk factor for diabetes (14, 22), it cannot inform the initial decision to screen because its diagnosis requires prior completion of a gold-standard diabetes screening test. As such, prediabetes is very useful in targeting repeat screening to individuals at high risk for diabetes, but its usefulness as a risk factor is limited because most individuals with prediabetes remain undiagnosed and overall screening rates are suboptimal (19).

Although the ADA does not recommend random glucose as a screening test for diabetes and does not provide guidance to interpret RBG values (4), random glucose is commonly used as an opportunistic screen for diabetes in clinical practice (23, 24). However, abnormal RBGs are frequently overlooked and failure to pursue gold-standard diabetes testing in response to elevated RBG values is common (25). Although the International Diabetes Federation recommends that individuals with a random glucose value 100–199 mg/dL (5.6–11.0 mmol/L) undergo formal diabetes testing, this recommendation is absent from U.S. guidelines. Our finding that a single RBG at least 100 mg/dL (5.6 mmol/L) is more strongly associated with undiagnosed diabetes than any single traditional diabetes risk factor supports the consideration of random glucose as a diabetes risk factor. Our demonstration of a strong dose-response relationship between the magnitude of the random glucose elevation and an increased risk for diabetes further supports this recommendation. Importantly, modest elevations in RBG values (100–119 mg/dL; 5.6–6.6 mmol/L) that are commonly ignored in clinical practice (23, 25) were strongly associated with undiagnosed disease. Together, these findings suggest that nondiagnostic, RBG values are an important indicator of dysglycemia that could play a critical role in screening and case identification strategies.

The usefulness of random glucose values in the diagnosis of diabetes and prediabetes has a strong physiologic basis. Glucose homeostasis is a tightly regulated function of β cell insulin production and insulin sensitivity (26) such that glucose concentrations are maintained in a narrow range (27). Disruptions in glucose homeostasis initially manifest as impaired glucose tolerance and increased glucose variability (26). In clinical practice, this is reflected as nondiagnostic RBG elevations and increased glucose variability. Given that random glucose testing accounts for greater than 95% of glucose testing in clinical practice (23), opportunities to recognize random glucose abnormalities and incorporate them into risk assessment exist in routine clinical practice.

Although random glucose is not currently included in U.S. diabetes screening guidelines, our findings demonstrate the potential importance of random glucose values in screening strategies. Existing studies demonstrate that a single RBG at least 125 mg/dL (6.9 mmol/L) is a good predictor of diabetes (28) and performs as well as more complicated models based on age, BMI, and race (29). We demonstrate that RBG values as low as 100 mg/dL (5.6 mmol/L) confer a significant risk for diabetes and are associated with undiagnosed diabetes. Our findings suggest that a hypothetical screening strategy in which individuals with a single RBG at least 100 mg/dL (5.6 mmol/L) undergo gold-standard diabetes screening and the ADA diabetes screening guidelines, which incorporate multiple risk factors, have similar associations with undiagnosed disease. In addition, the random glucose strategy, even after adjustment for other risk factors, is more strongly associated with undiagnosed diabetes than the USPSTF guidelines, which likewise recommend screening based on a single risk factor.

A major strength of this study is that the data are nationally representative of the noninstitutionalized, civilian, U.S. population without diagnosed diabetes and prediabetes. However, there are several limitations. First, our analyses are limited to cross-sectional associations between a single RBG value and glycemic status. Because of this, we are unable to examine the development of diabetes over time. Second, individuals with diagnosed diabetes and prediabetes were excluded based on self report; however, self-reported diabetes is both highly sensitive and specific for diagnosed diabetes (30). Third, because we sought to detect cases of undiagnosed diabetes and prediabetes, we were unable to examine prediabetes as a risk factor for undiagnosed diabetes. However, most individuals with prediabetes remain undiagnosed (2). In addition, our estimates of the association between the ADA guideline and undiagnosed disease likely underestimate the true association given our inability to include all ADA screening criteria in our definitions. Fourth, our analyses use serum glucose values rather than plasma glucose values. However, analytic differences between serum and plasma glucose values are small and unlikely to exceed the day-to-day biologic variation of glucose (31). Thus, our findings reflect real-world practice where serum glucose values are routinely obtained as part of chemistry panels. Fifth, our analyses focus on community-dwelling NHANES participants and may not directly translate to medical practice if patients are acutely ill. Sixth, our definition of prediabetes and diabetes was based on HbA_1C criteria alone because individuals examined in a fasting state did not have random glucose data available. As a result, our findings likely underestimate the burden of undiagnosed prediabetes and diabetes (32).

In conclusion, our findings suggest that a single RBG value at least 100 mg/dL (5.6 mmol/L) is a robust risk factor for type 2 diabetes and should prompt clinicians to obtain gold standard diabetes screening tests to categorize glycemic status. Considering the large number of individuals in the United States with undiagnosed diabetes and prediabetes (2), our findings have important implications for screening and case finding strategies. First, our findings highlight the importance of RBG values at least 100 mg/dL (5.6 mmol/L) as a risk factor for diabetes and provide evidence to support the inclusion of RBG values at least 100 mg/dL as a risk factor in U.S. diabetes screening guidelines. Second, our findings suggest that increased awareness of abnormal random glucose values and targeted diabetes testing may improve diabetes detection among individuals engaged in clinical care. Given the high frequency of glucose testing in clinical practice and the growing repository of computerized laboratory data within electronic medical records, the development of automated, glucose-driven risk assessment strategies may improve the screening and diagnosis of type 2 diabetes in clinical practice.