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Short (4 hours) and long-term (4 weeks) stability of prothrombin time (PT), activated partial thromboplastin time (APTT) and fibrinogen (FBG) in citrate plasma samples

BACKGROUND-AIM: Manufacturer (Siemens, Germany) states that PT is stable in citrate plasma up to 24h at room temperature (RT), whereas aPTT and Fbg should be determined within 4h after sample collection. While long-term storage (for up to 2 weeks) at ≤-20 °C is declared for aPTT, data for PT and Fbg are not provided by the manufacturer. The aim of this study was to verify manufacturer’s claims for sample stability for PT, aPTT and Fbg. METHODS: We measured PT (Innovin), aPTT (Actin FS) and Fbg (Multifibren U) in 20 citrate plasma samples (baseline results) on BCS XP coagulation analyzer (Siemens, Germany). Plasma samples were kept in a primary tube at RT and measurements were repeated after 4h and 24h. Two plasma aliquots were stored at ≤-20 °C and measurements were repeated after 2 and 4 weeks. Statistical analysis was performed using the MedCalc Statistical Software version 16.2.0 (MedCalc Software bvba, Ostend, Belgium). The results were tested with Friedman test. P <0.5 was considered significant. CROQALM (Croatian Quality Assessment in Laboratory Medicine) criteria were used as acceptable bias: ±15% for PT, ±7% for aPTT and ±14% for Fbg. RESULTS: Bias for PT at 4h and 24h at RT was not statistically significant (P=0.382). Clinically significant bias for PT was observed in 5/20 samples stored for 24h. During 24h storage at RT, aPTT and Fbg values differed statistically (P<0.001), but not clinically. There was no clinically significant difference for PT and Fbg in samples stored up to 4 weeks at -20 °C. However, we observed both clinically and statistically significant difference in aPTT values (P<0.001) stored for 2 and 4 weeks at -20 °C CONCLUSIONS: We have confirmed manufacturer’s claims for PT, aPTT and Fbg short-term stability (up to 4h) at RT in primary tubes. Our findings for long-term stability of aPTT contradict manufacturer’s claims. While not declared by the manufacturer, long-term stability at -20 °C for PT and Fbg was acceptable up to 4 weeks.

preanalytical phase, plasma stability, manufacturer’s claims, coagulation

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