Objective: To compare four assays for the measurement of GH following provocative tests and to assess the projected clinical decisions, which would have been based on their respective results.
Design: Multiple assays of serum samples obtained during provocative tests for GH response.
Subjects: Forty-seven children with short stature, who underwent clinical evaluation 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 by three other immunoassays: Sorin-IRMA (B), DPC-RIA (C) and Wallac-DELFIA (D). Results were classified as low, partial and normal GH response, corresponding to <10, 10-17.9 and >18 microIU/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 different (p<0.0001). Further analysis using paired t-test has shown highly significant differences between the assays (p<0.0001) apart from assays A and B that were not significantly different. Clinical grouping by the four tests was profoundly different: by assay A, 14.9% were judged low response and 57.4% normal; by assay D, 36.2% were low and only 21.3% normal. Kappa statistics 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 indications for GH therapy are based on laboratory GH results, more must be done to ensure uniformity and comparability of the GH assays.