Contributions of Glucose and Hemoglobin A1c Measurements in Diabetes Screening

Lee H. Hilborne, MD, MPH, DLM(ASCP); Caixia Bi, PhD; Jeff Radcliff; Martin H. Kroll, MD; Harvey W. Kaufman, MD


Am J Clin Pathol. 2022;157(1):1-4. 

In This Article


This study identified discrepancies between glucose and HbA1c levels to identify patients at risk for prediabetes or diabetes. The USPSTF last issued a grade B recommendation favoring "screening for abnormal blood glucose as part of cardiovascular risk assessment in overweight adults aged 40 to 70, followed by intensive behavioral counseling to promote a healthful diet and physical activity when glucose abnormalities are found."[12] In 2021, the USPSTF proposed lowering the recommended screening age to begin diabetes screening at 35 years.[13] Regarding screening, the USPSTF notes that "glucose abnormalities can be detected by measuring HbA1c or fasting plasma glucose or with an oral glucose tolerance test."[13]

Our findings suggest that glucose or HbA1c testing alone when screening for abnormalities of glucose metabolism could miss or delay diagnosis of prediabetes or diabetes for many patients. Medicare coverage of glucose[8] but not HbA1c[9] testing would be sufficient if glucose and HbA1c were clinically equivalent for screening. Our data suggest otherwise. More than 1 in 4 patients 60 years of age and older with glucose within the reference range had elevated HbA1c results. Even among younger patients, 12.9% (54,493/422,195) of individuals who had glucose within the reference range had elevated HbA1c results Table 1. These findings align with those of the Canadian Task Force on Preventive Care.[7]

The likelihood of claim denial was approximately 9 times greater for Medicare Advantage beneficiaries than for commercial insurance beneficiaries. Denials were higher for patients with Managed Medicaid than for patients with Medicaid FFS, likely reflecting alignment with payment policies incorporated into Medicaid contracts managed by the same commercial plans that manage Medicare Advantage programs.

Study limitations include lack of clinical data and evaluating only requisitions with ICD-10 code Z13.1. Although code Z13.1 should, by coding guidelines, exclude patients with known altered glucose metabolism, 11.1% of these requisitions contained a glucose abnormality diagnostic code. The combination of elevated glucose with normal HbA1c levels likely reflects inadequate fasting, transient hyperglycemia, or early-stage disease. Many factors limit the correlation between HbA1c and glycemia (eg, age, ethnicity, hemoglobinopathy), but screening services for patients at high risk for important conditions should focus on sensitivity over specificity, with further investigation or follow-up based on clinical considerations.

Our findings suggest that glucose and HbA1c are complementary when screening for glucose abnormalities, and excluding either test could delay diagnosis and management in many patients. Further studies should assess the time delay caused by routinely excluding HbA1c as part of diabetes screening and the magnitude of the differences. We encourage guideline developers and health plans to recognize that glucose and HbA1c provide complementary information and together offer improved clinical utility for diabetes screening.