Comparison of a new procalcitonin assay from roche with the established method on the brahms kryptor.

Procalcitonin (PCT) is a 13-kDa peptide and a precursor of calcitonin. In a healthy population, PCT concentrations are negligible (1 ). In systemic bacterial and fungal infections, plasma concentrations are raised, whereas concentrations remain fairly low in infections of viral or nonspecific cause (2 ). Recent studies have demonstrated the potential of PCT as a parameter to guide antibiotic therapy in different groups of patients, i.e., patients with chronic obstructive pulmonary disease experiencing respiratory tract infections (3, 4 ). The most frequently used medical decision points at which the use of antibiotic therapy is considered are 0.25 g/L and 0.50 g/L, depending on the patient population (3, 4 ). The first PCT assays were based on manual immunochemistry methods (Brahms PCT LIA). These assays have been replaced by fully automated immunochemistry methods (Brahms Kryptor, Brahms LIAISON, Olympus SphereLight 180). Recently, the PCT assay has been modified for use on a consolidated routine immunochemistry analyzer, the Roche Modular E170 system. We evaluated the analytical performance of this new assay by following the EP10 protocol, a document from the Clinical and Laboratory Standards Institute to test precision, linearity, recovery, carryover, and drift. Samples were prepared at different concentrations, from 0.24 –2.85 g/L. Three aliquots of each concentration were assayed on 5 different days, in a specific assay order. The within-run CV ranged from 3.0% for the lowest concentration to 1.3% for the highest concentration. The between-day CV ranged from 6.3% for the lowest concentration to 2.8% for the highest. These levels of imprecision were comparable with those reported for the PCT assay on the Brahms Kryptor (5 ). The mean recovery was 99%. There was no evidence of nonlinearity or sample carryover. The limit of quantification, i.e., the lowest concentration of analyte that can be quantified with a between-run imprecision of 20%, met the manufacturer’s specification of 0.06 g/L. In addition, we compared the new PCT assay from Roche on the Modular 170 with the widely accepted PCT assay from Brahms on the Kryptor (5 ). For analytical comparison, we used 229 samples of patient serum obtained from 195 different patients who were admitted to our hospital for lower respiratory tract infections (81, exacerbation of chronic obstructive pulmonary disease; 114, pneumonia). The patients participated in an ongoing study in our hospital on the etiology of exacerbations of chronic obstructive pulmonary disease, a study approved by the local ethics committee. Samples were also collected from 34 patients after antibiotic treatment. The majority of the serum samples were obtained within 24 h of admission. Samples not immediately analyzed were stored at 80 °C until analysis. PCT concentrations ranged from 0.02 g/L (limit of detection, i.e., the lowest concentra-