Table 2.
Reasons Why the HbA1c Measurement Gives a False Low or False High.
| Physiological causes | ||
|---|---|---|
| False low | False high | |
| Red blood cell production | Increased | Slowed by the lack of available iron |
| High altitude | Anemia induced by iron deficiency | |
| Pregnancy | Anemia induced by infection | |
| Hemorrhages, blood loss | Anemia induced by tumors | |
| Blood transfusion | ||
| Administration of erythropoietin | ||
| Iron supplementation | ||
| Red blood cell destruction | Premature | Late |
| Hemolytic anemia | Splenectomy | |
| Chronic kidney failure | Aplastic anemia | |
| Cirrhosis of the liver | ||
| Folic acid deficiency | ||
| Hemoglobinopathies: HbS, HbC, HbD | Hemoglobinopathies: HbH, HbF (thalassemia) | |
| Spherocytosis | ||
| Options for objective determination | ||
| • Determination of an “HbF-purified” HbA1c | ||
| • Reticulocytes plus ferritin | ||
| • Urea | ||
| • Hb-electrophoresis | ||
| • In the case of Hb variants, determine HbA1c with an immunological method | ||
| • Fructosamin | ||
| Laboratory causes and options for avoidance | ||
| False high—only in HPLC HbA1c measurements by carbamylation | ||
| Terminal kidney failure, uraemia, creatinine > 5 mg/dl | ||
| Alcoholism (acetaldehyde) | ||
| Aspirin (upward of 500 mg/day over weeks) | ||
| False high—only in immunological HbA1c measurements | ||
| Beta-lactam antibiotics | ||
| Contraceptive pill | ||
| HydroxyethyI starch | ||
| Options for objective determination | ||
| • Newer HPLC columns are no longer influenced by carbamylation, ask the laboratory | ||
| • Request a laboratory method other than HPLC (written note on the laboratory request form): immunological or enzymatic method | ||
| Other causes | ||
| False low | False high | |
| Nutritional (alcohol, fat) | Drugs: immunosuppressants, protease inhibitors | |
| Genetic hyperglycation in certain ethnic groups | ||
| Elderly patient | ||
| Organ transplant | ||
| Hypertriglyceridemia | ||
| Hereditary causes | Hereditary causes | |
Source: Compiled by C. von Boxberg, Leverkusen, Germany.