Analytical Validation of the IMMULITE(®) 2000 XPi Progesterone Assay for Quantitative Analysis in Ovine Serum

SIMPLE SUMMARY: Consumer demand for sheep food products are on the rise, thus resulting in shifts in sheep production systems. These shifts require a better understanding of reproductive health in various production systems through research and implementation of these improved reproductive management strategies. To do this it is necessary to utilize safe, timely and accurate tools to measure key reproductive markers. Circulating progesterone concentration is a commonly used reproductive marker in ewes as it can be used to monitor female cyclicity. We evaluated how well the IMMULITE(®) 2000 XPi (Siemens) measured progesterone concentrations in sheep serum. This system is optimized for use in human clinical settings, and we know that the sample type can influence system performance therefore our objective was to determine the analytical performance of the machine using sheep serum samples spiked with known concentrations of progesterone over the manufacturers reported readable range. Experiments were conducted in accordance with guidelines recommended by the Quality Assurance and Laboratory Standard committee of the ASVCP. Variability within and between runs as well as on independent machines fell within acceptable deviation, therefore we concluded that use of the IMMULITE(®) 2000 XPi (Siemens) is a safe, timely and accurate system to measure circulating progesterone concentrations in sheep serum. ABSTRACT: Monitoring circulating progesterone (P4) concentration is an important component of basic and applied reproduction research and clinical settings. IMMULITE(®) 2000 XPi (Siemens) is a newly upgraded fully automated immunoassay system marketed for human use to measure concentrations of different analytes including P4. Our objective was therefore to characterize the analytical performance of the IMMULITE(®) 2000 XPi P4 immunoassay across the reportable range in ovine serum. This validation of analytical performance included determining (1) linearity, (2) precision through within-run, and between-run coefficient of variation (CV) calculations, (3) accuracy through bias calculations for spiking-recovery bias and interlaboratory (range and average based) bias for two laboratories across the reportable range (0.2–40 ng/mL). The average within-run and between-run precision (CV%) across the reportable range of the IMMULITE(®) 2000 XPi P4 immunoassay for serum P4 concentration were both <5%, ranging between 2–8%. The average Observed Total Analytic Error (TEo) reported here for serum P4 concentration across the reportable range was ~30%, ranging from 14.8–59.4%, regardless of the considered bias. Based on these data we conclude that the automated IMMULITE(®) 2000 XPi P4 immunoassay provides a precise, accurate, reliable, and safe method for measuring P4 concentration ovine serum.