Analytical evaluation of the performances of Diazyme and BRAHMS procalcitonin applied to Roche Cobas in comparison with BRAHMS PCT-sensitive Kryptor

Background: Procalcitonin (PCT) is a recognized marker of sepsis, and its use is expanding to antibiotic stewardship. The aim of this study was the evaluation of two methods: Diazyme PCT on Roche Cobas c702 (PCT-D) and BRAHMS PCT on Roche Cobas e602 analyzers (PCT-BR) in comparison with BRAHMS PCT-sensitive Kryptor (PCT-BK). Methods: Imprecision was assessed at six critical concentrations following the CLSI EP5-A3; limits of detection (LoDs) were checked according to CLSI EP17-A2; linearity was tested, and method comparison was performed on 239 serum samples. Results: Overall CVs ranged from 12.58% to 5.97% for PCT-D, from 3.94% to 1.70% for PCT-BR and from 6.57% to 1.90% for PCT-BK. LoDs were 0.143 mu g/L, 0.014 mu g/L, 0.040 mu g/L for PCT-D, PCT-BR and PCT-BK, respectively. The functional assay sensitivity was 0.24 mu g/L for PCT-D, 0.045 mu g/L for PCT-BK and <0.035 mu g/L for PCT-BR. PCT-BR was linear up to 68.7 mu g/L, PCT-BK up to 43 mu g/L and PCT-D up to 27.2 mu g/L. Method comparison: PCT-D = 0.6543 PCT-BK + 0.014, r = 0.8463 (but 0.44 if calculated on 0-5 mu g/L range); PCT-BR = 0.9125 PCT-BK + 0.021, r = 0.9917. Cohen's. ranged from 45.2% at 0.25 mu g/L to 57.0% at 2.00 mu g/L between PCT-D and PCT-BK, whereas it ranged from 89% to 81.3% between PCT-BR and PCT-BK. Conclusions: The PCT-D performances were significantly different from those of PCT-BR and PCT-BK regarding sensitivity, precision, linearity and agreement at clinical cutoffs. For some patients with serial testing, significantly deviating results were obtained compared to reference. In contrast to Roche PCT assay, it does not seem feasible to use BRAHMS PCT cutoffs for the Diazyme test.