Verification of the T50 Calciprotein Crystallization test: Bias estimation and interferences

Objectives: The T50 Calciprotein Crystallization test (T50 test) is a novel blood-based in vitro diagnostic assay that determines the calciprotein crystallization time in patients. It is based on the one-half maximum transition time of calciprotein particle 1 (CPP1) to calciprotein particle 2 (CPP2) in serum, as detected by nephelometry. To date, the T50 test has only been performed at Calciscon AG, where the assay has been developed and is manufactured. The aim of this study was to compare the agreement and precision of the T50 test in a routine clinical laboratory. Additionally, the interference of free hemoglobin, bilirubin, lipid and low molecular weight heparin (LMWH) was analyzed in the T50 test. Methods: Serum samples were measured at both laboratory sites to determine the agreement. The CLSI EP15-A3 protocol was used to evaluate the precision. Interference was analyzed by spiking pooled serum samples with interfering analytes. Results: Both laboratories showed excellent agreement in the T50 values (y=1.002x-4). Furthermore, high precision was observed for the clinically relevant lower range of T50 with a total variation coefficient of 6.4 %. Serum samples with mid and higher ranges of T50 failed the CLSI precision criteria with a total variance of 10.1 % and 6.2 %, respectively. Lastly, no interferences were observed within the normally observed clinical serum concentrations of free hemoglobin, bilirubin, lipid, and LMWH. Conclusions: The T50 test was successfully implemented in a routine laboratory setting. Additionally, the precision and interference observed in this study largely agreed with the manufacturer’s claims.