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

Glycosylated haemoglobins: biochemical evaluation and clinical utility

A review is given of the biochemical background of the glycosylated haemoglobins, their methods of determination, and their clinical significance. Special attention is paid to the sample preparation. For all methods except the colorimetric TBA-method, the removal of the labile pre-HbA1c fraction is essential. Under proper conditions, high-performance liquid chromatography, agar-gel electrophoresis and affinity chromatography are suitable methods for use in the clinical laboratory for the estimation of HbA1c and HbA1. However, the colorimetric TBA-method must be considered to be the method of choice. The clinical utility of the test is stressed with special respect to the management of diabetic pregnancies, the control of home-monitoring of blood glucose, and the objective measurement of the effect of changing diabetic therapy.

Recent advances in glycosylated hemoglobin measurements

Glycosylated hemoglobins have gained wide acceptance as an accurate index of long-term blood glucose control in diabetes mellitus. A variety of glycosylated hemoglobin assays is available. There is a high degree of correlation between results determined by these assays. The ideal laboratory method for measuring glycosylated hemoglobin in the diabetic should be accurate, precise, easily standardized, inexpensive, and rapidly performed. Unfortunately, none of the currently used methods meet all of the criteria necessary to be considered the ideal laboratory method. The most widely used methods for quantitating glycosylated hemoglobins--including ion exchange chromatography, electrophoresis, isoelectric focusing, thiobarbituric acid colorimetry, and affinity chromatography--are reviewed with respect to the important advantages and disadvantages of each method for the clinical laboratory. Techniques for quantitating glycosylated proteins other than hemoglobins, such as albumin, are also discussed.

A new colorimetric method for the estimation of glycosylated hemoglobin

A new colorimetric method, based on the phenol sulphuric acid reaction of carbohydrates, is described for the determination of glycosylated hemoglobin. Hemolyzates were treated with 1 mol/l oxalic acid in 2 mol/l Hcl for 4 h at 100 degrees C, the protein was precipitated with trichloroacetic acid, and the free sugars and hydroxymethyl furfural in the protein free supernatant were treated with phenol and sulphuric acid to form the color. The new method is compared to the thiobarbituric acid method and the ion-exchange chromatographic method for the estimation of glycosylated hemoglobin in normals and diabetics. The increase in glycosylated hemoglobin in diabetic patients as estimated by the phenol-sulphuric acid method was more significant (P less than 0.001) than the increase observed by the thiobarbituric acid method (P less than 0.01). The correlation between the phenol-sulphuric acid method and the column method was better (r = 0.91) than the correlation between the thiobarbituric acid method and the column method (r = 0.84). No significant correlation between fasting and postprandial blood sugar level and glycosylated hemoglobin level as determined by the two colorimetric methods was observed in diabetic patients.