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When A1c can mislead
A1c depends on red blood cells and hemoglobin. Anything that changes them can push the result up or down.
Changes in red blood cell lifespan
Conditions that change how long red blood cells live can change A1c. NIDDK lists recent blood loss, sickle cell disease, erythropoietin treatment, hemodialysis and transfusion (NIDDK).
Low iron
A falsely high A1c can occur in people who are very low in iron, for example with iron-deficiency anemia (NIDDK).
Kidney and liver disease
Kidney failure and liver disease are other causes of false A1c results (NIDDK).
Hemoglobin variants
People of African, Mediterranean or Southeast Asian descent, or with family members who have sickle cell anemia or thalassemia, may carry a hemoglobin variant that interferes with some A1c tests. Most carriers have no symptoms and do not know. Not all A1c tests are affected; a different test method can be used (NIDDK). The NGSP keeps information on which methods suit which variants (NGSP).
Pregnancy
A1c may be used early in pregnancy to look for diabetes that was present before. Gestational diabetes is usually checked with glucose tests between 24 and 28 weeks (NIDDK).
Signs something is off
Doctors may suspect interference when A1c and glucose results do not match (NIDDK). See A1c high, glucose normal for every reason the two can disagree. If you use a CGM, a large gap between your GMI and your lab A1c is worth raising too (Bergenstal 2018).
Normal test variation
Even on the same sample, repeat tests vary a little. NIDDK gives the example that a 6.8% result could read anywhere from 6.4% to 7.2% on a repeat test (NIDDK). A retest that comes only a few weeks after a change can also look stuck; see how fast A1c can change. Home kits have a wider margin than labs; see home A1c tests.
Sources
- National Institute of Diabetes and Digestive and Kidney Diseases (NIH). The A1C Test & Diabetes. www.niddk.nih.gov/health-information/diagnostic-tests/a1c-test
- NGSP. IFCC Standardization of HbA1c: the IFCC and NGSP master equation (NGSP = 0.09148 x IFCC + 2.152). ngsp.org/ifccngsp.asp
- Bergenstal RM, Beck RW, Close KL, et al. Glucose Management Indicator (GMI): a new term for estimating A1C from continuous glucose monitoring. Diabetes Care. 2018;41(11):2275-2280. doi.org/10.2337/dc18-1581
Written and maintained by the controla1clevels.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-10-25. Spotted an error? See About.