A comparative evaluation of glycosylated haemoglobin assays: feasibility of references and standards

Abstract

Four assays; high pressure liquid chromatography, colorimetric with thiobarbituric acid, affinity columns, and microcolumn cation exchange were compared for (1) ability to discriminate between samples taken from diabetic and normal subjects; (2) correlation with each other; (3) stability over time at different temperatures; and (4) reproducibility between laboratories. The most discriminatory (10 samples from a diabetic and 10 samples from a normal group) was the microcolumn cation exchange method (t=5.25; pp1a+b and a decrease in the haemoglobin A_1c. Haemoglobin A_1c was reproducible for 4 days when stored at 4 °C and up to 11 days when stored at -80 °C. Samples exchanged between centres at 4 °C and performed within 5 days by high pressure liquid chromatography for haemoglobin A₁ and haemoglobin A_1c correlated well (r=0.98 and 0.99). Samples exchanged between centres after storage (up to 40 days -80°C) correlated (r=0.99) by the thiobarbituric acid method. Thus, standards can be prepared for the thiobarbituric acid method and this method with high pressure liquid chromatography could be used to establish references for clinical assays.