Glycated albumin by affinity chromatography and radioimmunoassay in the management of diabetes mellitus

Abstract

A sensitive and specific assay for glycated albumin (GALE) has been developed. Ten pL of serum is fractionated by affinity chromatography on a boranateagarose column and quantitated by radioimmunoassay (RIA). Assay linearity is 15.6-1,000 ng of albumin. Dose-response curves prepared from both glycated albumin and albumin standard are superimposable in the range of 31-500 ng, equivalent to 0.1-15% of GALB assuming total albumin concentration to be 50 glL. Recovery was 93 f 3%. Sensitivity is 16 ng. Precision (CV) is 14.3% with patient sample duplicates (n = 57) and 15.6% when assaying controls (n = 21). Our reference interval (RI) for GALE is 0.43-1.19% of total albumin. GALB levels are significantly elevated (p < 0.0001) in random samples from 37 diabetics. GALB correlates positively with both glycated hemoglobin (GHB) (r = 0.901) and serum glucose concentration (r = 0.706). In 10 diabetic patients followed serially with fasting and postprandial glucoses, GALB, and GHB, GALE was more sensitive than GHB in reflecting short-term changes in glycemic control. Our data demonstrate the value of GALB measurements when the assessment of glycemic control over a short period of time is important, such as in monitoring the results of changing therapy.

HPLC assay for serum glycated albumin

“…A commercial assay kit, for example, yields much higher results (normal range 5.%10.7%) [3] than the reference range of 1.5-2.6% which was (incorrectly) cited for this method. Others report reference ranges as low as 0.4-1.1, again for affinity chromatographic separation [4]. Such discordant results show that glycated albumin affinity chromatography is only a semiquantitative method.…”

Rate of Formation of Glycated Albumin Revisited and Clinical Implications

“…Given that normal values for glycated albumin using affinity chromatography methods range from  0.6 to 1.4-3% [26,27] and that similar reference range values (0.5-1.5%) are reported with an immunoassay that employs the monoclonal antibody [18] site specific for albumin modified by Amadori glucose adducts (Exocell, Phila), it is unclear why the enzymatic assay yields values higher than those observed with such methods [26,27] but methodologic aspects are relevant. Complexation with boronate or monoclonal antibody may be restricted to one cis-hydroxyl group per albumin molecule, the resin may require two glucose groups per molecule to effectuate binding [28], and/or the number of binding sites in the resin be inadequate for the number of glucose-modified sites.…”