Assessment of GH status in adults with GH deficiency using serum growth hormone, serum insulin‐like growth factor‐l and urinary growth hormone excretion

Abstract

Summary OBJECTIVES The benefits of treating adults with G H deficiency are now well recognized although the criteria for deciding which patients to treat are still not clear. At present the ‘gold standard’ Is the Insulin stress test (IST) which Is unpleasant and potentially dangerous, particularly in patients with hypopituitarism. The aim of this study was to determine whether alternative methods of assessing GH status are reliable in predicting GH deficiency. SUBJECTS AND METHODS Forty‐four patients with unequivocal G H deficiency (peak 1ST <2mU/l) and 17 with partial deficiency (peak 1ST 2‐10 mU/I) were studied. Each patient was assessed clinically with respect to the number of other pituitary axes affected and biochemically with an estimate of urinary G H excretion (uGH) and serum IGF‐I. These markers were then related to GH status as defined by Insulin stress testing. MEASUREMENTS Insulin stress tests were performed using 0.1 units/kg I.v. and accepted with a blood glucose <2mmol/l. Serum GH and IGF‐I were measured by radioimmunoassay whilst uGH was estimated by an Immunoradlometric assay using commercially available reagents. uGH was estimated from the mean of two overnight urine collections which consisted of all urine passed from last voiding through to the first morning sample. RESULTS The presence of unequivocal G H deficiency (peak 1ST <2mu/l) was predictable if 2 or more other pituitary axes were affected (90%). U G H declined significantly with the level of peak 1ST response ( P < 0‐001) and almost so with the number of other deficient hypothalamic‐pituitary axes affected ( P = 0‐057). Thus, u G H accurately reflected G H status and showed good separation from normal controls In patients less than 40 years (specificity 79%) and between 40 and 60 years (specificity 67%). Above this age the method is less specific (36%). Patients excreted significantly less G H than controls in all three age groups ( P < 0.01). Subnormal levels of IGF‐I were strongly predictive of unequivocal G H deficiency (91 % with subnormal IGF‐I have a peak 1ST G H lt; 2 mU/l) although a normal value does not reliably exclude the diagnosis. CONCLUSIONS A diagnosis of adult G H deficiency can be reliably made without the need for an insulin stress test by using a combination of low urinary G H excretion, subnormal I G F‐I levels and clinical assessment with regard to the number of other pituitary axes affected.