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Spontaneous growth hormone (GH) secretion is evaluated by measurement of the 24-hour integrated concentration of GH (24-hour IC-GH), a major diagnostic procedure, or by shorter protocols such as monitoring 6 h during sleep. We have evaluated several possibilities for shortening the procedure by comparing the results of an abbreviated procedure to the 24-hour IC-GH studies. The study population consisted of 50 children with classic GH deficiency (group GHD), determined by provocative testing, and 45 children who had a subnormal secretion of GH (group N), determined by low 24-hour IC-GH but normal GH provocative tests. Twenty-two children of normal height and stature served as a control group. All the children were prepubertal, while there was no overlap between the lower 5th percentile of the 24-hour IC-GH of the control subjects (3.3 micrograms/l) and the upper 97th percentile of the 24-hour IC-GHs of the N and GHD groups (2.9 and 2.7 micrograms/l, respectively), there was a considerable overlap between the IC-GH of control subjects and that of the GHD and N groups measured in all the abbreviated blood withdrawal protocols, except for the 10-hour daytime and the 12-hour nighttime protocols of the GHD patients. It should be noted that there was only a small overlap between the control and the GHD groups during the 12-hour daytime protocol. We have found that the longer the blood collection period the greater the sensitivity and the specificity. We conclude that the 24-hour IC-GH test is the best diagnostic tool for identifying children with subnormal GH secretion.

We measured the ratio of GH by radioreceptor assay (RRA) using IM-9 cells to its radioimmunoassay (RIA) level in: (a) 25 children and young adults with normal growth (controls); (b) 7 poorly growing children with GH neurosecretory dysfunction (GHND) who had normal stimulated GH but subnormal integrated concentration of GH (IC-GH) who responded to GH therapy; (c) 4 poorly growing children who had both normal stimulated GH and IC-GH but did not respond to GH therapy (GHNR - GH responder), and (d) 7 poorly growing patients with normal stimulated, and IC-GH who responded to GH therapy (GHR - GH responder). The RRA/RIA ratio of the GHND group was 1.3 +/- 0.4 similar to that of the control group - 1.3 +/- 0.3. The mean RRA/RIA ratio of the 7 GHR patients was 0.6 +/- 0.5, significantly lower than the controls and the GHND patients (p < 0.05). The RRA/RIA ratios of the 4 GHNR patients was not different from the controls. We conclude that: (1) GH binding is normal in GHNR and GHND patients and (2) RRA/RIA ratio below the normal range as measured by IM-9 cell GH RRA in short, poorly growing children with normal GH secretion, was a predictor of the response to GH therapy.