Hemoglobin A1c

Interpretation

• Approximates 90-day random blood glucose

$$ Avg Glucose \approx 1.59 \times HbA1c - 2.59 $$

• Normal <5.7%
• Elevated 5.7% to 6.4%
• Diabetes ≥6.5%

Falsely high

• It can be elevated in people whose red blood cells have a longer lifespan
  • Vitamin B12 and iron deficiency
  • Splenectomy
• Also laboratory artifact
  • Aspirin
  • Cigarette carboxyhemoglobin
  • Hb S, G, D, C, and E
  • Hypertriglyceridemia
  • Hyperbilirubinemia
• Others
  • Afro-Caribbeans (+0.4%)
  • Chronic renal failure

Falsely low

• It can be decreased by anything that shortens the lifespan of red blood cells
  • Hemolysis
  • Blood loss
  • Spherocytosis
  • Thalassemia HbS
  • Supplementation with erythropoietin
  • Supplementation with iron or vitamin B12
• Also laboratory artifacts
  • Sickle cell HbF
• Others
  • Vitamin A or C supplementation
  • HIV antiretrovials
  • Chronic liver disease
  • Chronic renal failure

Alternatives

• Fructosamine
• Self-monitored capillary blood glucose