QUANTIFICATION OF URINARY GROWTH HORMONE (GH) EXCRETION BY CENTRIFUGAL ULTRAFILTRATION AND RADIOIMMUNOASSAY: APPRAISAL OF THE RELATIONSHIP BETWEEN 24 H URINARY GH AND MEAN 24 H SERUM GH LEVELS IN NORMAL AND ABNORMAL STATES OF GH SECRETION

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Abstract
We have applied a simple method for the quantification of 24 h urinary GH excretion (24 h UGH), combining centrifugal ultrafiltration and radio‐immunoassay (RIA), to an appraisal of the relationship between 24 h UGH and mean 24 h serum GH levels in normal and abnormal states of GH secretion. Forty‐four subjects, comprising 13 normal adults, 12 short‐statured subjects and 19 subjects with active acromegaly, underwent blood sampling at 20‐min intervals and concurrent urine collection for 24 h. Mean 24 h serum GH and 24 h UGH were also determined in four post‐menopausal women before and during cyclical oestrogen replacement therapy, and 24 h UGH was measured in six normal men prior to and following the subcutaneous administration of biosynthetic GH (0.2 IU/kg). Each subject's mean 24 h serum GH level was determined by assaying a ‘pooled’ sample, derived from equal aliquots of the 73 serum samples obtained during the 24 h study. The method for quantification of 24 h UGH employs centrifugal microconcentrators, and involves a 50‐fold concentration of urine, followed by dialysis and RIA. Surface adsorptive hormone loss during sample collection and ultrafiltration is minimized by the prior addition of bovine serum albumin to the urine collection container. Immunoreactive GH in ultrafiltered urine dilutes in parallel with the RIA standard curve. GH is stable in urine stored at −20°C for at least 12 months. There was a highly significant correlation between 24 h UGH and mean 24 h serum GH values obtained from the combined population of normal adults (including the post‐menopausal women during oestrogen therapy) and short‐statured subjects (r=0.69, P> 0.0001). A significant correlation was also found in short‐statured subjects alone (r= 0.63, P > 0.05). In contrast, there was no significant correlation between 24 h UGH and mean 24 h serum GH in subjects with active acromegaly, and their 24 h UGH values were not distinguishable from those of the ‘non‐acromegalic’ subjects. A significant increase in 24 h UGH occurred in the post‐menopausal women given cyclical oestrogen replacement therapy (9.7 ± 2.6 (mean ± SE) to 24.6 ± 1.0 μIU/mmol creatinine, P> 0.02), reflecting the increase in their mean 24 h serum GH levels (0.8 ± 0.3 to 5.3 ± 0.7 mIU/l, P > 0.01). Twenty‐four hour UGH increased from 4.6 ± 0.6 to 17.1 ± 2.1 μIU/mmol creatinine (P > 0.002) in the men given biosynthetic GH. Twenty‐four hour UGH measurements reflect mean 24 h serum GH levels in normal adults and short‐statured subjects. While the measurement of 24 h UGH shows promise as an investigative tool, our results cast doubt on its use in the diagnosis of acromegaly.