A-323 Pre-analytic Interference in PT and PTT Measurement using Mechanical vs Optical Clot Detection

Abstract

Abstract Background Mechanical clot-detection is commonly thought to be less susceptible to optical pre-analytic interference. Pediatric specimens are particularly prone to be hemolyzed and/or icteric. Our hospital laboratory approached an impending change in coagulation instrumentation from mechanical (STAGO) to optical (IL) with some trepidation. We, therefore, performed a detailed comparison of plasma samples containing a broad range of hemoglobin, bilirubin, and triglyceride using IL reagents (RecombiPlasTin2G, SynthASil) on the TOPS 550 and a manual method on the STart 4. Methods 7 independent pools (5 normal, 2 prolonged) of residual citrated plasma were supplemented with hemoglobin, bilirubin, or triglyceride up to 1000 mg/dL, 150 mg/dL, or 750 mg/dL, respectively, or with equal volumes of vehicle as control. Supplementation was confirmed and quantified by measuring HIL indices on a Roche Cobas 6000. PT and PTT were performed in duplicate on each experimental and control sample on the TOPS and STart systems. Imprecision of the two systems was monitored at two levels throughout the study. Results Imprecision (n = 20) of the TOPS PT and PTT assays ranged from 1.4–3.1% (CV). Imprecision (n = 20) of the STart PT and PTT assays ranged from 1.9–18.3% (CV). PT and PTT on both platforms were not impacted by hemolysis or lipemia up to an H index of 1000 and an L index of 500, respectively. As shown in the Figure, PT and PTT in normal pools on both platforms were significantly prolonged by the presence of bilirubin above an I-index of 30. Results were similar in the prolonged pools. Data points are the means (± SD) of 10 determinations across the 5 normal plasma pools for experimental (●) and control specimens (○). Conclusion Mechanical clot detection did not show superior resistance to pre-analytic interference vs an optical clot detection method.