Validation of the minimal citrate tube fill volume for routine coagulation tests on ACL TOP 500 CTS®.

INTRODUCTION: CLSI recommends a minimal citrate tube fill volume of 90%. A validation protocol with clinical and analytical components was set up to determine the tube fill threshold for international normalized ratio of prothrombin time (PT-INR), activated partial thromboplastin time (aPTT) and fibrinogen. METHODS: Citrated coagulation samples from 16 healthy donors and eight patients receiving vitamin K antagonists (VKA) were evaluated. Eighty-nine tubes were filled to varying volumes of >50%. Coagulation tests were performed on ACL TOP 500 CTS(®) . Receiver Operating Characteristic (ROC) plot, with Total error (TE) and critical difference (CD) as possible acceptance criteria, was used to determine the fill threshold. RESULTS: Receiving Operating Characteristic was the most accurate with CD for PT-INR and TE for aPTT resulting in thresholds of 63% for PT and 80% for aPTT. By adapted ROC, based on threshold setting at a point of 100% sensitivity at a maximum specificity, CD was best for PT and TE for aPTT resulting in thresholds of 73% for PT and 90% for aPTT. For fibrinogen, the method was only valid with the TE criterion at a 63% fill volume. CONCLUSION: In our study, we validated the minimal citrate tube fill volumes of 73%, 90% and 63% for PT-INR, aPTT and fibrinogen, respectively.

Evaluation of three commercial ELISA kits for anticardiolipin and anti-beta2-glycoprotein I antibodies in the laboratory diagnosis of the antiphospholipid syndrome.

INTRODUCTION: The laboratory criteria of the antiphospholipid syndrome (APS) include lupus anticoagulant (LAC), anticardiolipin antibodies (aCL) and anti-ß2glycoprotein I antibodies (aß2GPI) IgG or IgM. METHODS: We evaluated three commercial ELISAs for aCL and aß2GPI IgG and IgM: Asserachrom® ('Stago'), Bio-Rad ('BR') and the Bindazyme™ (the Binding Site, 'BS'). RESULTS: Results of all assays and of LAC were correlated with the clinical background (n=228). Sensitivity for Stago/BS/BR aCL IgG was 14%/15%/18%, for aCL IgM 1%/5%/4%, for aß2GPI IgG 9%/10%/17% and for aß2GPI IgM 4%/4%/3%. The specificity for Stago/BS/BR for all assays ranged from 86% to 98%. The positive predictive value (PPV) for Stago/BS/BR aCL IgG was 46%/52%/40%, for aCL IgM 8%/36%/19%, for aß2GPI IgG 70%/67%/45% and for aß2GPI IgM 23%/23%/20%. Combining LAC with aCL and aß2GPI antibodies increased the sensitivity (Stago/BS/BR IgG: 26%/27%/31%, IgM: 22%/21%/26%) and PPV (Stago/BS/BR IgG: 41%/46%/36%, IgM: 34%/40%/36%). Comparing the diagnostic power of the tests, only Stago/BS aß2GPI IgG had a Chi-square P-value lower than 0.05. The combination of LAC and IgG ELISAs of BS resulted in the lowest P-value (0.098) compared to the other combinations. CONCLUSION: All evaluated ELISAs are a practical tool in the laboratory diagnosis of APS. The diagnostic performance shows slight differences between the ELISAs from the different manufacturers.