Choosing the calibration model in assay validation

Data transformations and weighting schemes are normally used to obtain the best-fit of standard curves in bioanalysis and the calibration model is usu ally selected during prevalidation. In the present study, a comparison has been made between unweighted and weighted (1/x, 1/x(2), and 1/root x) regre ssion models with or without an intercept in achieving the best-fit for the standard curve of CDRI compound 81/470, a new anthelmintic agent, in cow m ilk. Validation samples in milk at the LLOQ, medium, and high concentration s were also analysed by each of the calibration models. An unweighted regre ssion equation with an intercept overestimated the concentrations at the LL OQ. An unweighted equation without intercept and weighted equations with or without an intercept significantly minimized the bias at the LLOQ without distorting the results at higher concentrations. Hence, an unweighted equat ion for a straight line passing through the origin was found to be the best model for a standard curve of 81/470 in milk. Similar results were obtaine d for 81/470 and UMF-078 in serum and plasma, respectively. Bioanalysts sho uld routinely test these models to obtain the best fit model for their cali bration curves as part of their assay validation not during prevalidation. (C) 1999 Elsevier Science B.V. All rights reserved.