Evaluation of very rapid emit Qst methods for measuring serum procainamide and N-acetylprocainamide concentrations

This study assessed the Emit Qst procainamide (PA) and N-acetylprocainamide (NAPA) assays. Accuracy and intraday precision were evaluated by repeatedly measuring PA and NAPA concentrations in spiked serum samples using Qst and high-performance liquid chromatography methods. Interday precision was evaluated by measuring concentrations in spiked samples over 4 weeks. Correlation between methods was assessed in patient samples, and proportional, constant, and random errors were estimated. Intraday coefficients of variation (CVs) were below 6.4% for PA and NAPA for both methods; interday CVs were below 7.8%. The proportional, constant, and random errors of the PA Qst assay in patient samples were 5.7%, -0.224 mg/L, and +/- 0.574 mg/L, respectively. The same errors in the NAPA Qst assay were 17.2%, 0.229 mg/L, and +/- 1.79 mg/L, respectively. The Qst assays are rapid, accurate, and precise methods for routine clinical measurement of PA and NAPA, although the proportional error in the NAPA assay should be recognized.