Measurement of Urinary Growth Hormone (GH) Levels by Highly Sensitive Enzyme Immunoassay as a Potential Screening Test for GH Secretion

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We set up a highly sensitive enzyme immunoassay of human growth hormone (hGH) using anti-hGH rabbit Fab'-peroxidase conjugate. IgG was obtained from anti-hGH rabbit serum with salting-out and diethylaminoethyl cellulose. IgG was digested by porcine gastric mucosa pepsin to F (ab')_2 which was reduced to Fab'. Fab' was conjugated with peroxidase by maleimide method. The minimum detectable amount of hGH was 0.3pg/ml using 100μl of dialyzed urine sample without any concentrating procedure. Urinary GH was detectable in all normal subjects. In order to evaluate the measurement of urinary GH as a potential screening test of pituitary disorders, we examined 706 subjects in a population (19 to 80 years old). Urine and plasma samples were collected in the early morning after overnight fasting. Urinary creatinine and β_2-microglobulin levels were measured by autoanalyzer and specific radioimmunoassay, respectively. Urinary GH levels ranged from not detectable to 314 ng/g creatinine in these subjects. The logarithmus of these data showed a normal distribution. The normal range obtained from 58 male and 98 female subjects were 0.5 to 17.0ng/g creatinine and 1.2 to 41.9ng/g creatinine, respectively. Urinary GH levels were elevated in 48 out of the 706 subjects examined (6.8%). However, 13 out of these 48 subjects (1.8%) were acoompanied by increased urinary β_2-microglobulin (>200μg/g creatinine), suggesting that urinary GH levels are influenced by renal tubular dysfunction. In contrast, urinary GH was not detectable in 6 out of the 706 cases (0.8%), suggesting possible hypopituitarism. These results indicate that measurement of urinary GH by highly sensitive enzyme immunoassay was useful for a potential screening test for pituitary dysfunction although the renal function should be considered simultaneously.