Pitfalls of HbA1c in the Diagnosis of Diabetes

Abstract

<jats:title>Abstract</jats:title> <jats:p>Many health care providers screen high-risk individuals exclusively with an HbA1c despite its insensitivity for detecting dysglycemia. The 2 cases presented describe the inherent caveats of interpreting HbA1c without performing an oral glucose tolerance test (OGTT). The first case reflects the risk of overdiagnosing type 2 diabetes (T2D) in an older African American male in whom HbA1c levels, although variable, were primarily in the mid-prediabetes range (5.7-6.4% [39-46 mmol/mol]) for many years although the initial OGTT demonstrated borderline impaired fasting glucose with a fasting plasma glucose of 102 mg/dL [5.7 mmol/L]) without evidence for impaired glucose tolerance (2-hour glucose ≥140-199 mg/dl ([7.8-11.1 mmol/L]). Because subsequent HbA1c levels were diagnostic of T2D (6.5%-6.6% [48-49 mmol/mol]), a second OGTT performed was normal. The second case illustrates the risk of underdiagnosing T2D in a male with HIV having normal HbA1c levels over many years who underwent an OGTT when mild prediabetes (HbA1c = 5.7% [39 mmol/mol]) developed that was diagnostic of T2D. To avoid inadvertent mistreatment, it is therefore essential to perform an OGTT, despite its limitations, in high-risk individuals, particularly when glucose or fructosamine and HbA1c values are discordant. Innate differences in the relationship between fructosamine or fasting glucose to HbA1c are demonstrated by the glycation gap or hemoglobin glycation index.</jats:p>

Polycystic ovary syndrome and type 2 diabetes mellitus: A state-of-the-art review

“…Furthermore, available studies evaluating the ability of HbA1c to detect IGT and diabetes in PCOS have found that the test has low sensitivity when compared with OGTT for the assessment of glucose tolerance[ 66 , 67 ]. Finally, the diagnostic accuracy of HbA1c in detecting T2D has recently been questioned, with some investigators arguing strongly in favor of OGTT for this procedure[ 77 ].…”

Continuous glucose monitoring and 1-h plasma glucose identifies glycemic variability and dysglycemia in high-risk individuals with HbA1c < 5.7%: a pilot study

“…Consistent with previous findings, subjects with a 1-h high PG level had greater GV indices which included MAGE, SD, and LI, compared to those with 1-h low levels [ 9 ]. Moreover, 1-h PG ≥ 155 mg/dL (8.6 mmol/L) during an OGTT is a sensitive predictor for future development of diabetes, cardiovascular risk, and mortality [ 4 , 11 , 12 ].…”

<p>The Oral Glucose Tolerance Test: 100 Years Later</p>

“…63,64 Various drugs have also been associated with changes in HbA1c levels independent of blood glucose variations. [65][66][67] HIV patients treated with immunosuppressive agents may have HbA1c discordant with blood glucose levels which therefore results in an underestimation in the prevalence of dysglycemia; 68 the HbA1c, therefore, should not be used to assess glycemia in this population. 69 To summarize, although HbA1c is a valuable tool for the diagnosis of dysglycemia, screening for high-risk individuals using the HbA1c alone may not be sufficient to substitute for the information derived from OGTT.…”

“… 63 , 64 Various drugs have also been associated with changes in HbA1c levels independent of blood glucose variations. 65 – 67 HIV patients treated with immunosuppressive agents may have HbA1c discordant with blood glucose levels which therefore results in an underestimation in the prevalence of dysglycemia; 68 the HbA1c, therefore, should not be used to assess glycemia in this population. 69 …”