Growth hormone in urine: development of an ultrasensitive assay applicable to plasma and urine.

A radiometric assay for human growth hormone (HGH) was developed based on a polyclonal goat anti-HGH antiserum covalently coupled to nonsedimenting polyacrylamide particles. HGH can be specifically immunoextracted from sample volumes of up to 10 ml. Subsequently, bound HGH is identified and quantitatively measured by a 125I-labelled monoclonal anti-HGH antibody. The assay is insensitive to plasma proteins from 10 to greater than 90%, to changing NaCl and urea molarities and to pH ranges from 6 to 8. The sensitivity in the second incubation is 2 pg/tube, corresponding to a maximum sensitivity of 300 fg/ml of a sample volume of 10 ml (urine) or of 40 pg/ml, if a volume of 50 microliter (plasma) is assayed. In healthy children, a mean HGH excretion of 6.5 ng/24 h was found with a large interindividual range from undetectable to 37.4 ng. An important intraindividual night-to-night variation of HGH excretion was found in several subsequent first morning void samples in healthy children. The mean excretion in 13 HGH-deficient children was 0.9 ng/24 h off therapy and increased to a mean of 6.9 ng/24 h on therapy. In acromegalic patients, the excreted HGH amounted to 73-208 ng/24 h. Preliminary results suggest that the ultrasensitive assay applied to plasma and urine could be a considerable improvement of diagnosis and follow-up of disorders of HGH secretion.