Point-of-care testing of the international normalized ratio in patients with antiphospholipid antibodies

Stephanie L. Perry; Gregory P. Samsa; Thomas L. Ortel

doi:10.1160/TH05-06-0400

Thrombosis and Haemostasis, Table of Contents

Thromb Haemost 2005; 94(06): 1196-1202
DOI: 10.1160/TH05-06-0400

Blood Coagulation, Fibrinolysis and Cellular Haemostasis

Schattauer GmbH

Point-of-care testing of the international normalized ratio in patients with antiphospholipid antibodies

Authors

Stephanie L. Perry

¹Division of Hematology, Department of Medicine
Gregory P. Samsa

²Center for Clinical Health Policy Research, Duke University Health System, Durham, North Carolina, USA
Thomas L. Ortel

¹Division of Hematology, Department of Medicine

³Department of Pathology, and

Abstract

Summary

Antiphospholipid antibodies can influence the results of clotting tests in a subset of patients, which can be a major obstacle in monitoring warfarin. The aim was to determine if point-of-care testing of the International Normalized Ratio (INR) is influenced by antiphospholipid antibodies. We compared 59 patients receiving warfarin for a diagnosis of antiphosphoipid antibody syndrome (APS) to 49 patients receiving warfarin for atrial fibrillation to evaluate the consistency between INR results obtained by different methods. INR results obtained by finger stick (capillary whole-blood) and venipuncture (non-citrated and citrated whole-blood) were compared with our laboratory plasma-based prothrombin time assay. Five patients (8%) with APS and both elevated anti-β₂glycoprotein I levels and positive lupus anticoagulants had non-measurable ProTime^® INR results and generally higher Hemochron^® Signature INR results than the plasma-based method, but the corresponding chromogenic factor X results were not supratherapeutic. For the remaining patients, differences between the plasma-based INR and the point-of-care INR results ranged from 0.2±0.2 to 0.4±0.3. The differences were similar for patients with APS and atrial fibrillation for all INR comparisons with the exception of the plasma-based method compared with the ProTime, which showed a mean absolute difference of 0.4±0.3 for APS patients and of 0.2±0.2 for atrial fibrillation patients (p=0.02). In a subset ofAPS patients, the ProTime^® system will not yield an INR result and the HEMochron Signature (citrate and non-citrate whole-blood) INR results will exhibit elevated INR results. For this subset of APS patients, we suggest using an alternative method to monitor warfarin.

Keywords

Antiphospholipid antibodies - antiphospholipid antibodysyndrome - international normalized ratio - point-of-care testing - prothrombin time - warfarin

Full Text

References

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