Study summary · research use only
Diagnosis of growth hormone deficiency in adults by testing with GHRP-6 alone or in combination with GHRH: comparison with the insulin tolerance test
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
This human study compared GH stimulation testing with GHRP-6 alone or combined with GHRH to the insulin tolerance test (ITT) for diagnosing adult growth hormone (GH) deficiency. Twenty patients underwent ITT for suspected pituitary or adrenal disease, then received GHRP-6 alone or GHRP-6 plus GHRH on separate days. Ten patients had a GH peak below 3 microg/l on ITT and were classified as GH deficient; the remainder were classified as GH sufficient, with peak GH differing between groups on both the GHRP-6 and GHRP-6+GHRH tests. The only side effect reported with GHRP-6 was flushing. The authors reported that GH peak cutoffs below 7 microg/l (GHRP-6) and below 13 microg/l (GHRP-6+GHRH) correctly identified all ITT-defined GH-deficient patients, and described the GHRP-6-based tests as showing similar sensitivity and specificity to ITT.
Abstract
The diagnosis of GH deficiency in adults should be made using provocative testing of GH secretion. The insulin tolerance test (ITT) is recommended as the gold standard investigation. Because of the risk of serious complications, patients with epilepsy or known ischemic heart disease should not undergo this test. GHRP-6 is a synthetic hexapeptide that releases GH by binding to specific hypothalamic and pituitary receptors. We assessed the diagnostic capability of GH stimulation by GHRP-6 alone or in combination with GHRH in comparison to the results of an ITT. Twenty patients underwent an ITT for suspected pituitary or adrenal disease. Either GHRP-6 (1 microg/kg) alone, or GHRP-6 in combination with GHRH (1 microg/kg) were administered on different days. Blood samples were obtained during a subsequent 90-min period for measurement of GH. Ten patients had a GH peak response of less than 3 microg/l during ITT and were considered growth hormone deficient (GHD). The GH mean peak (+/-S.E.M., range) in this group was 0.7 microg/l (+/-0.3, 0.1-2.9) compared with 14.5 microg/l (+/-3.5, 3.8-40.8) in the group of patients with a GH peak response of more than 3 microg/l (growth hormone sufficient (GS)). For the GHRP-6 test, the GH mean peak was 1.3 microg/l (+/-0.6, 0.1-6.7) in the GHD group versus 25.7 microg/l (+/-5.5, 7.7-54.2) in the GS group. After GHRP-6+GHRH, the GH mean peaks were 4.0 microg/l (+/-1.3, 0.2-11.9) versus 54.7 microg/l (+/-11.1, 13.9-136.0) respectively. During administration of GHRP-6, the only side effects observed were flush symptoms. Peak GH levels below 7 microg/l for the GHRP-6 test and below 13 microg/l for the combined GHRP-6+GHRH test identified all patients with GH deficiency correctly as defined by ITT. The results suggest that testing with GHRP-6 or GHRP-6+GHRH is as sensitive and specific as an ITT for the diagnosis of adult GH deficiency.
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