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

Abstract and Introduction


Objectives: Given the long-term consequences of untreated diabetes, patients benefit from timely diagnoses. Payer policies often recognize glucose but not hemoglobin A1c (HbA1c) for diabetes screening. This study evaluates the different information that glucose and HbA1c provide for diabetes screening.

Methods: We conducted a retrospective review of national clinical laboratory testing during 2020 when glucose and HbA1c were ordered for routine diabetes screening, excluding patients with known diabetes, out-of-range glucose, or metabolic syndrome.

Results: Of 15.47 million glucose and HbA1c tests ordered simultaneously, 672,467 (4.35%) met screening inclusion criteria; 116,585 (17.3%) were excluded because of diabetes-related conditions or the specimen was nonfasting, leaving 555,882 result pairs. More than 1 in 4 patients 60 years of age or older with glucose within range had an elevated HbA1c level. HbA1c claims were denied more often for Medicare beneficiaries (38,918/65,273 [59.6%]) than for other health plans combined (23,234/291,764 [8.0%]).

Conclusions: Although many health plans do not cover HbA1c testing for diabetes screening, more than 1 in 4 glucose screening patients 60 years of age or older with an in-range glucose result had a concurrent elevated HbA1c result. Guideline developers and health plans should explicitly recognize that glucose and HbA1c provide complementary information and together offer improved clinical utility for diabetes screening.


Diabetes is the seventh-leading cause of death in the United States, accounting for more than 3% of all deaths in 2017.[1] Diabetes also contributes to heart, cerebrovascular, and kidney diseases. Diabetes disproportionately affects older people (≥50 years of age) and people of color.[2] Optimal diabetes screening facilitates early intervention to mitigate progression of prediabetes and reduces the long-term consequences of diabetes.[3]

Diagnostic criteria for diabetes have been refined over the years.[4] Initial criteria were primarily based on measuring glucose, but point glucose measurement is problematic because some patients with impaired glucose tolerance or diabetes have glucose levels within the reference range at the time of the measurement. Detection of impaired glucose metabolism, therefore, benefits from a diagnostic approach that simultaneously measures long-term glucose exposure.

In 1969, Rahbar described an increase in an "unusual" hemoglobin in patients with diabetes, now recognized as glycated hemoglobin, or hemoglobin A1c (HbA1c).[5] HbA1c reflects average blood glucose over several months, whereas glucose measurement represents a specific point in time. HbA1c measurement has become standard practice for the evaluation of diabetes control in patients with known diabetes.[6] HbA1c measurement is also useful for diabetes screening.[7] In 1993, the American Medical Association's Current Procedural Terminology Editorial Panel granted a category I code for reporting HbA1c. Glucose and HbA1c continue to be reimbursed, with appropriate indications and intervals, by Medicare and other insurers.[8,9]

Glucose measurement is approved by Medicare as a screening benefit for at-risk asymptomatic patients without diabetes when reported with International Classification of Diseases, Tenth Revision (ICD-10) code Z13.1, "Encounter for screening for diabetes mellitus."[10] HbA1c measurement, however, is presently not covered for screening (Z13.1).[9] Medicare applies specific criteria to determine whether a screening service, generally an uncovered benefit, will be covered. Specifically, the service must be (1) reasonable and necessary for the prevention or early detection of illness or disability, (2) recommended with a grade of A or B by the United States Preventive Services Task Force (USPSTF), and (3) appropriate for Medicare beneficiaries.[11]

Asymptomatic individuals who present for routine screening generally receive diagnostic laboratory tests that include a basic or comprehensive metabolic panel in addition to other medically appropriate services, such as HbA1c testing. USPSTF guidelines indicate that screening for glucose abnormalities may include either glucose or HbA1c (grade B).[12] The "or" implies that HbA1c may be duplicative when accompanied by a concurrent glucose measurement. Glucose is a component of commonly ordered metabolic panels.

On March 16, 2021, the USPSTF released a revised draft of Screening for Prediabetes and Type 2 Diabetes Mellitus.[13] The proposed revisions continue to recommend diabetes screening for at risk-patients and states that moderate net benefit exists when screening is coupled with effective preventive measures. The revised recommendation states that screening is effective in younger at-risk populations (adults aged 35 to 70 years who are overweight or obese). As proposed, the recommendations acknowledge the benefits of HbA1c screening and discuss the diagnosis of prediabetes or diabetes using a fasting glucose, HbA1c, or oral glucose tolerance test. The recommendations do not, however, address situations where glucose and HbA1c results are discrepant with respect to disease classification when used for asymptomatic population screening.

To assess the potential impact of excluding HbA1c as a screening benefit, we evaluated the frequency of discrepant glucose and HbA1c results in patients screened for diabetes.