Temperature dependence of the chromatographic assay of hemoglobin A1 and application of a temperature controlled assay to clinical evaluation of diabetic control

We investigated the temperature dependence of the cation-exchange chromatographic properties of hemoglobin A1 using the "Fast Hemoglobins Test System" obtained from Isolab, Inc., Akron, OH, U.S.A. and a temperature control chamber constructed in our laboratory. Six patient samples, two each from the "normal" range (5--8.5%, "transitional" range (8.5--12.0%) and "uncontrolled diabetic" range (12--20%) described by Isolab (as measured at 24 degrees C) were collected, hemolyzed and assayed according to product insert instructions. Each sample was assayed in triplicate in three separate runs at 20 degrees C, 22 degrees C, 24 degrees C, 26 degrees C and 28 degrees C in the temperature controlled (+/- 0.25 degrees C) chamber. Resultant mean increases in assay results of 0.8, 1.1 and 1.6% hemoglobin A1 per 2 degrees C increase in temperature for the three ranges respectively, indicate that the temperature dependence of the microcolumn assay for hemoglobin A1 is at least partially a function of the relative percentage of glycosylated hemoglobin in the sample. By controlling assay temperature we have reduced interassay variation throughout all concentration ranges by more than one-half to less than 5%. We applied this temperature controlled assay to measurement of hemoglobin A1 levels in 33 non-diabetic subjects and to the screening of hemoglobin A1 levels in 77 diabetic patients regularly attending the diabetic-endocrine outpatient clinic of this hospital. No non-diabetic subject had a HbA1 level above 8.5% and of the diabetic patients, 26% fell within the "normal" range, 43% within the "transitional" range and 31% within the "uncontrolled diabetic" range.