#2124 Accuracy and interferences in the T50 test: assessing the reliability of a novel diagnostic tool

Abstract Background and Aims A novel blood-based in vitro diagnostic test determines the calcification propensity in patients, e.g. chronic kidney disease (CKD) patients. This assay is known as the ‘T50 test’ and is based on the one-half maximal transition time (T50; minutes) of calciprotein particle 1 (CPP1) to calciprotein particle 2 (CPP2) in serum (Fig. 1). Numerous studies have associated a lower T50 with cardiovascular and all-cause mortality in chronic kidney disease (CKD) patients at stages 3, 4 and 5, kidney transplant recipients, and in the general population. To date, the T50 test has been performed at a single site (Calciscon AG, Biel, Switzerland). The aim of this study was to determine the accuracy of the T50 test. Additionally, the effect of haemolysis, hyperbilirubinemia and lipidemia interferences on the T50 was studied and compared to the manufacturer's claims. Method The T50 was measured using T50 test kits and according to the protocol of Calciscon AG using an automatic pipetting machine (EVOware Freedom, Tecan) and a nephelometer (NEPHELOstar, BMG). Patient serum samples were spiked with haemoglobin, bilirubin, or lipids (triglyceride) for the interference analysis. In total, three dilution series with interferences and four additional non-spiked patient serum samples were included (n = 32). The T50 of all samples were measured at two laboratory sites: Amsterdam UMC (Amsterdam, The Netherlands) and Calciscon AG. Data were statistically analysed for accuracy using the Passing Bablok regression and the Bland Altman plot. Interference was established with deviations >10% in T50 compared to the control sample. Results The measurements of all samples at both sites were similar with a mean bias of 0.24% (±4.84%) and a great agreement was found (slope = 1.012; 95% CI [0.931 to 1.107]) (Table 1). Interference was observed at higher levels of haemoglobin and triglyceride with concentrations of at least 0.1 g/dL and 1124.8 mg/dL, respectively. The triglyceride interference is in agreement with the manufacturer's claim (>1000 mg/dL) in contrary to haemoglobin (>0.3 g/dL). No interference was detected for bilirubin with concentrations up to 59.8 mg/dL. Conclusion The accuracy of the T50 test was high with nearly identical T50 results between two laboratory sites. Furthermore, no interference was observed within usual clinical ranges of haemoglobin, bilirubin, and lipid levels. Interference was present at extremely high values only.