EVALUATION OF GROWTH-HORMONE ASSAYS USING RATIO PLOTS

To permit comparison between growth hormone (GH) results obtained usin g the Pharmacia polyclonal assay and the Delfia monoclonal assay, we u sed both methods to measure GH concentrations in peak GH responses to the pyridostigmine-growth-hormone-releasing-hormone (PD-GHRH) test and in unstimulated samples from 40 healthy adults and 31 patients with s uspected GH deficiency. Ratio plots were used for the comparison, and acceptability criteria were based on inherent analytical imprecision a nd on analytical quality specifications. The mean ratio (r; Pharmacia/ Delfia) for the peak GH responses in 40 healthy adults was calculated to be 1.59, and the 95% prediction interval for ratios fulfilling the imprecision criterion was applied. For GH values >1 mIU/L, the peak an d unstimulated GH ratios in healthy adults and patients were within th e 95% prediction interval, and fulfilled the biological criterion as w ell. Therefore, the conversion factor of 1.59 is applicable for the ev aluation of GH-stimulation tests.