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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

Stephanie L. Perry
1   Division of Hematology, Department of Medicine
,
Gregory P. Samsa
2   Center for Clinical Health Policy Research, Duke University Health System, Durham, North Carolina, USA
,
Thomas L. Ortel
1   Division of Hematology, Department of Medicine
3   Department of Pathology, and
› Author AffiliationsFinancial support: This research was conducted in the General Clinical Research Clinic at Duke University Health System (grant# MO1-RR-30, National Center for Research Resources, General Clinical Research Centers Program, National Institutes of Health) and was supported by the International Technidyne Corporation, ITC, Edison, NJ. Dr. Perry received support from a K-12 award (grant# RR17630–03).
Further Information

Publication History

Received 06 June 2005

Accepted after resubmission 14 September 2005

Publication Date:
07 December 2017 (online)

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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
 

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