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


Glucose and HbA1c tests were ordered together 15,468,174 times during the study period; 26,043 (0.16%) result pairs were excluded for missing demographic or payer data. Paired results that included ICD-10 code Z13.1 totaled 672,467 (4.4%). Of these, 74,334 (11.1%) were excluded because of a reported ICD-10 code suggesting a glucose abnormality and 42,251 (6.2%) were identified as nonfasting. Of the remaining 555,882 result pairs (227,072 [40.8%] from females), 407,967 (73.4%) had glucose within the reference range, of which 61,042 (15.0%) had elevated HbA1c. Conversely, of 147,915 (26.6%) pairs with elevated glucose, 71,991 (48.7%) had HbA1c levels within the reference interval Table 1.

Having an in-range glucose level was more common in women (255,760/328,810 [78%]) than in men (152,207/227,072 [67%]). The frequency of elevated HbA1c (≥5.7% [39 mmol/mol]) among pairs with in-range glucose was slightly higher for women (15.9% [95% CI, 15.8%-16.0%]) than for men (14.4% [95% CI, 14.4%-14.5%]). HbA1c levels increased with increasing age group Table 1; among patients 60 years of age and older with in-range glucose, 25.8% (21,266/82,360) had elevated HbA1c levels. Although most (59,041 [96.7%]) patients with a glucose level under 100 mg/dL (5.55 mmol/L) and an elevated HbA1c level had HbA1c levels in the prediabetes range (5.7%-6.0% [39-42 mmol/mol]), some (2001 [3.3%]) had HbA1c levels in the overt diabetes range (>6.5%) (Figure 1, Supplementary Table 1, Supplementary Figure; all supplemental material can be found at American Journal of Clinical Pathology online).

Figure 1.

Cumulative distribution of hemoglobin A1c (HbA1c) based on glucose categories (within reference interval, prediabetes, diabetes) from all 555,882 paired HbA1c and glucose results. Vertical dashed lines highlight diagnostic HbA1c thresholds for prediabetes (left) and diabetes (right), calendar year 2020.

Few differences existed by payer type except for Medicare: 21.7% of Medicare beneficiaries and 14.7% of patients with other insurance had glucose levels within the reference range but elevated HbA1c levels that could suggest either prediabetes or diabetes. Coverage denial rates for HbA1c were substantially higher for Medicare fee-for-service (FFS) (21,045/31,734 [66.3%]) and Medicare Advantage (17,873/33,539 [53.3%]) beneficiaries than for Medicaid (1307/18,901 [6.9%]), Managed Medicaid (7872/33,832 [23.3%]), or commercial insurance (14,055/239,031 [5.9%]) patients. (Supplementary Table 2).