HbA1c is widely used in the management of patients with diabetes mellitus (DM). Hb Louisville is an unstable hemoglobin that differs from HbA by the substitution of a phenylalanine residue for a leucine residue in position 42 of the b-chain, resulting in instability in the Hb molecule with increased erythrocytic destruction, clinically manifested as hemolytic anemia. The Hb Louisville heterozygotes suffer from a mild anemia, jaundice and hemolytic crisis. Abnormally low HbA1c concentrations are usually encountered in patients with high turnover rates of hemoglobin. Fructosamine is unaffected by disorders of red blood cells nor is influenced by hemoglobin variants, thus serving as an indicator of blood glucose concentrations of previous 2–3 weeks.
We report on three patients that belonged to the same family and had history of heterozygosity trait for Hb Louisville. All three patients had type 2 diabetes mellitus with falsely low HbA1c values (patient A: 2.8%, 2.9%, 3.2%; patient B: 4.4%, 3.8%, 3.7%; patient C: 4.2%, 4.6%, 3.7%). The patients had consistent elevation of fasting blood glucose values (patient A: 162, 171, 233 mg/dL; patient B: 262, 232, 235 mg/dL; patient C: 152, 130, 136 mg/dL). All three patients had evidence of hemolytic anemia, and their average hemoglobin levels were: patient A: 9.41 mg/dL, patient B: 10.9 mg/dL, patient C: 8.6 mg/dL. We therefore determined serum fructosamine levels, and the results were: patient A (patient deceased), patient B: 420 mcmol/L and patient C: 295 mcmol/L (Reference Range >285 mcmol/L).
Fructosamine serum level determination is advocated for glycemic assessment in diabetic patients with Hb Louisville when discrepancies between glucose measurements and HbA1c values>are encountered.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.