Urinary growth hormone excretion rates in normal and acromegalic man: a critical appraisal of its potential clinical utility

Abstract

The assessment of growth hormone (GH) secretory status is often difficult because of the intermittent nature of GH release and resulting wide swings in plasma GH levels. Urinary GH excretion holds promise as an index of integrated plasma GH free of this limitation, but technical problems have prevented its use until recently. We adapted a recently developed method for accurately measuring GH and its various molecular forms in urine to the determination of GH excretion rates. The method involves diafiltration and immunoextraction of GH from urine, with monitoring of recovery and final quantification by radioimmunoassay. Twenty-four h GH excretion rates were determined in 30 normal adults (15 men and 15 women) and 4 acromegalic patients. They ranged from 1 to 81 ng/24 h in men, from 1 to 70 ng/24 h in women and from 87 to 1660 ng/24 h in acromegaly (medians = 8.7, 18.0 and 267 ng/24 h, respectively). Excretion rates varied widely, not only between subjects, but also within the same subject on different days. Women and younger subjects tended to excrete more GH than men and older subjects, although these trends were not statistically significant. Acromegalics excreted significantly more GH than normals (p < 0.001). Twelve normal subjects underwent simultaneous assessment of 24 h integrated plasma GH (sampling every 20 min) and urine GH excretion. Urine GH correlated weakly (r = 0.45) with integrated plasma GH. We conclude that 24 h urinary GH excretion may provide a useful, non-invasive means of assessing GH secretory status at the extremes of secretory abnormality (e.g., acromegaly), but that its inherent variability and wide normal range may limit its usefulness in milder forms of pituitary dysfunction.