Comparison between four immunoassays for growth hormone (GH) measurement as guides to clinical decisions following GH provocative tests

Objective: To compare four assays for the measurement of GH following provo cative tests and to assess the projected clinical decisions, which would ha ve been based on their respective results. Design: Multiple assays of serum samples obtained during provocative tests for GH response. Subjects: Forty-seven children with snort stature, who underwent clinical e valuation and GH provocative tests. Methods: All samples were measured by the immunoassay Sorin-RIA (A), which is routinely used in our laboratory. Basal and peak samples were analyzed b y three other immunoassays: Sorin-IRMA (B), DPC-RIA (C) and Wallac-DELFIA ( D). Results were classified as low, partial and normal GH response, corresp onding to <10, 10-17.9 and > 18 mu IU/ml peak serum GH levels. Results: High correlation was found between individual results by the four kits (r = 0.92-0.94). However, the mean peak GH values were significantly d ifferent (p<0.0001). Further analysis using paired t-test has shown highly significant differences between the assays (p<0.0001) apart from assays A a nd B that were not significantly different. Clinical grouping by the four t ests was profoundly different: by assay A, 14.9% were judged low response a nd 57.4% normal; by assay D, 36.2% were low and only 21.3% normal. Kappa st atistics measurement demonstrated poor agreement between assays A and D and between B and D. Conclusion: As the criteria for the diagnosis of GH deficiency and the indi cations for GH therapy are based on laboratory GH results, more must be don e to ensure uniformity and comparability of the GH assays.