Abstract
In this thesis, the development of an immunoassay system for glycosylated albumin is described. The technique that was used consisted of affinity separation of glycosylated from non-glycosylated albumin, followed by an enzyme-linked immunosorbent assay (ELISA) for albumin. The assay sensitivity was 2mg/l and was sufficiently sensitive to measure the glycosylated albumin concentration in the urine and plasma of both diabetic and non-diabetic subjects. An overnight timed urine sample and blood sample were collected from 85 diabetic subjects (56 IDDM, 29 NIDDM) and 39 age and sex matched non-diabetic control subjects. Plasma and urinary glycosylated albumin, urinary alpha1-microglobulin, glycosylated haemoglobin, plasma and urinary creatinine were measured. Duration of diabetes, body weight and presence of retinopathy were noted. The diabetic subjects were grouped according to their albumin excretion rate (AER) and a relationship was found between urinary glycosylated albumin and albumin excretion rate. An association was found between increasing albumin excretion rate and elevated protein glycosylation and an enhanced excretion of glycosylated albumin was demonstrated. Affinity chromatography was used to measure glycosylated haemoglobin as part of the Islington Diabetes Survey. Some of the screening samples and almost all of the follow-up samples were measured. Three glycosylated haemoglobin methods were compared as screening tests for diabetes mellitus, the other methods were carried out at the Whittington Hospital. Affinity chromatography was found to have the highest specificity and predictive value (positive) tests of the three methods, and was shown to be potentially useful as a screening test. The recognition that protein glycosylation is increased in the diabetic state has resulted in investigation of its usefulness as a screening tool and of its involvement in the pathogenesis of diabetic complications. Glycosylated proteins may have a role in population screening for diabetes, and may be involved in, and indicative of, the development of the sequelae of diabetes mellitus.