Normal growth hormone response to the 75 g oral glucose tolerance test measured by immunoradiometric assay.

Abstract

Estimation of plasma growth hormone (GH) during a 50 g oral glucose tolerance test (OGTT) is widely used in the investigation of suspected acromegaly and in monitoring its response to treatment. A plasma GH of < 2 mUlL measured in terms of International Reference Preparation (I RP) 66/217 by radioimmunoassay (RIA) is considered normal in the majority of UK labora­ tories, although data from the UK External Quality Assessment Scheme reveal that cut-offs as low as I mUj l.; and as high as 10mUIL, are used. Two developments suggest a need for reapprai­ sal of the normal GH response. Firstly, since 1982 the 50 g OGTT has been superseded by a 75 g OGTT in the diagnosis of diabetes mellitus, I and it would seem desirable to standardise the pro­ cedure for both conditions. Secondly, the intro­ duction of sensitive immunoradiometric assays (IRMA) for GH has made it possible now to measure levels that are below the detection limit of most RIA This short study was performed, therefore, to define the normal plasma GH response measured by IRMA during a 75 g OGTT. The normal subjects comprised 16 men and 8 women (mean age 28·6 years, range 21-48) who did not abuse alcohol and had no clinical evidence of pituitary, liver or renal disease. They were fasted overnight and rested in the sitting position for 45 min prior to insertion ofa Venflow catheter in the antecubital fossa at - 30 min. Following two basal samples, at -IS and 0 min, 75 g of glucose in 200 mL water (freshly prepared) was given orally at 09.00 h. Blood was collected at 30 min intervals for ISO min into heparinised tubes on ice, and the plasma assayed for GH using the Boots-Celltech Sucrosep kit (Boots-Celltech Diagnotics Ltd, Slough, Bucks, UK), and glu­ cose. Samples from individual patients were all