A Novel Statistical Approach for the Comparison of Analytical Methods to Measure Angiotensin Converting Enzyme Activity, Enalaprilat, and Benazeprilat

Two different analytical techniques were used to measure angiotensin converting enzyme (ACE) activity, and three different methods were used to measure each of the ACE inhibitors enalaprilat and benazeprilat. All measurements were made in human plasma. The groups of methods were compared by two different statistical approaches. First, the means of the methods were compared by the paired t test or analysis of variance, depending on whether two or three different methods were under comparison. Second, the squared coefficients of variation of the methods were compared by the Jackknife technique. The dual statistical approach employed enabled both the accuracy and the variability of the analytical methods to be compared and is a superior approach to the inappropriate use of correlation coefficients that are commonly used to compare analytical techniques. No statistically significant difference was found between the two assays used to measure ACE activity. Differences were found between the three methods to measure enalaprilat, although no obvious reason could be found for this phenomenon. Significant differences were also found between the three methods used to measure benazeprilat and were attributed to the presence of metabolites interfering in the nonspecific assay methods.