TABLE 1

Common clinical conditions that can affect hemoglobin A1c ^a

Clinical condition	Effect on hemoglobin A1c	Mechanism or reason for effect
Asplenia	Increases hemoglobin A1c	Decreased red blood cell (RBC) turnover due to increased RBC life span
Chronic kidney disease	Effects vary based on severity of underlying disease and therapies	Increased hemoglobin A1c Carbamyl-hemoglobin production in uremic patients Erythropoietin deficiency Decreased hemoglobin A1c Shortened RBC survival Erythropoietin administration Hemodialysis (lowering of urea levels reduces carbamyl-hemoglobin concentration)
Chronic liver disease	Effects vary based on severity of underlying disease and therapies	Increased hemoglobin A1c Jaundice (increased glycation reaction in the presence of higher bilirubin concentrations) Decreased hemoglobin A1c Increased RBC turnover Antiviral drug therapies may decrease RBC life span
Hemoglobinopathies	Varies with testing method and assay	Multifactorial including anemia and rapid RBC turnover
Hemolytic anemia	Decreases hemoglobin A1c	Reduced RBC total volume Increased RBC destruction shortens RBC life span
Iron deficiency anemia	Increases hemoglobin A1c	Reduced RBC turnover prolongs RBC survival Greater malondialdehyde concentrations increase hemoglobin glycation reactions
Pregnancy	Decreases hemoglobin A1c in first 2 trimesters May increase hemoglobin A1c in third trimester	Increased RBC turnover decreases hemoglobin A1c Increased erythropoietin production decreases hemoglobin A1c Hemodilution decreases hemoglobin A1c
Transfusion	Variable hemoglobin A1c effects	Increased hemoglobin A1c Elevated glucose concentration in storage medium Decreased hemoglobin A1c Dilutional response
Vitamin B₁₂ and folate deficiency anemias	Increases hemoglobin A1c	Reduced RBC turnover prolongs RBC survival

↵a This summation represents most current literature and clinical practice, but should be used as a guide only and should not replace clinical assessment or decision-making.
Based on information in references 1–8.