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

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

› Author Affiliations

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

References
1 Moll S, Ortel TL. Monitoring warfarin therapy in patients with lupus anticoagulants. Ann Intern Med 1997; 127: 177-85.
2 Ortel TL, Manares C, Moore KD. et al Antiphospholipid Anitbodies and Use of the International Normalized Ratio. Blood 1998; 92: 42a.
3 Sanfelippo MJ, Sennet J, McMahon EJ. Falsely elevated INRs in warfarin-treated patients with the lupus anticoagulant. WMJ 2000; 62-4 43
4 Della Valle P, Crippa L, Safa O. et al Interference of lupus anticoagulants in prothrombin time assays: implications for selection of adequate methods to optimize the management of thrombosis in antiphospholipid-antibody syndrome. Haematologica 1999; 84: 1064-74.
5 Greaves M, Cohen H, Machin SJ. et al Guidelines on the Investigation and Management of the Antiphospholipid Syndrome. Br J Haematol 2000; 109: 704-15.
6 Lawrie AS, Purdy G, Mackie IJ. et al Monitoring of oral anticoagulant therapy in lupus anticoagulant positive patients with the anti-phospholipid syndrome. Br J Haematol 1997; 98: 887-92.
7 Robert A, Le Querrec A, Delahousse B. et al Control of oral anticoagulation in patients with the antiphospholipid syndrome – influence of the lupus anticoagulant on international normalized ratio. Thromb Haemost 1998; 80: 99-103.
8 Tripodi A, Chantarangkul V, Clerici M. et al Laboratory control of oral anticoagulant treatment by the INR system in patients with the antiphospholipid syndrome and lupus anticoagulant: Results of a collaborative study involving nine commercial thromboplastins. Br J Haematol 2001; 115: 672-8.
9 Tripodi A, Chantarangkul V, Clerici M. et al Laboratory diagnosis of lupus anticoagulants for patients on oral anticoagulant treatment: performance of dilute russell viper venom test and silica clotting time in comparison with staclot LA. Thromb Haemost 2002; 88: 583-6.
10 Brandt JT, Triplett DA, Alving B. et al Criteria for the Subcommittee on Lupus Anticoagulant / Antiphospholipid Antibody of the Scientific and Standardisation Committee of the ISTH. Thromb Haemost 1995; 74: 1185-90.
11 Wilson WA, Gharavi AE, Koike T. et al International Consensus Statement on Preliminary Classification Criteria for Definite Antiphospholipid Syndrome: Report of an International Workshop. Arthritis Rheum 1999; 42: 1309-11.
12 Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 307-10.
13 Westgard JO. Points of care in using statistics in method comparison studies. Clin Chem 1998; 44: 2240-2.
14 Rosove MH, Brewer PMC. Antiphospholipid thrombosis: Clinical course after the first thrombotic event in 70 patients. Ann Intern Med 1992; 117: 303-8.
15 Khamashta MA, Cuadrado MJ, Mujic F. et al The management of thrombosis in the antiphospholipidantibody syndrome. N Engl J Med 1995; 332: 993-7.
16 Ginsberg JS, Wells PS, Brill-Edwards P. et al Antiphospholipid antibodies and venous thromboembolism. Blood 1995; 86: 3685-91.
17 Crowther MA, Ginsberg JS, Julian J. et al A Comparison of two intensities of warfarin for the prevention of recurrent thrombosis in patients with the antiphospholipid antibody syndrome. N Engl J Med 2003; 349: 1133-8.
18 Le DT, Weibert RT, Sevilla BT. et al The International Normalized Ratio (INR) for monitoring warfarin therapy: Reliability and relation to other monitoring methods. Ann Intern Med 1994; 120: 552-8.
19 Kaatz SS, White RH, Hill J. et al accuracy of laboratory and portable monitor international normalized ratio determinations: Comparison with a criterion standard. Arch Intern Med 1995; 155: 1861-7.
20 Reed C, Rickman H. Accuracy of International Normalized Ratio determined by portable whole-blood coagulation monitor versus a central laboratory. Am J Health Syst Pharm 1999; 56: 1619-23.
21 Andrew M, Ansell JL, Becker DM. et al Point-of-Care Prothrombin Time Measurement for Professional and Patient Self-Testing Use: A Multicenter Clinical Experience. Am J Clin Pathol 2001; 115: 288-96.
22 Douketis JD, Lane A, Milne J. et al Accuracy of a portable International Normalization Ratio Monitor in outpatients receiving long-term oral anticoagulant therapy: Comparison with a laboratory reference standard using clinically relevant criteria for agreement. Thromb Res 1998; 92: 11-7.
23 Tripodi A, Chantarangkul Bressi C. et al International Sensitivity Index Calibration of the near-patient testing prothrombin time monitor, ProTime. Am J Clin Pathol 2003; 119: 241-5.
24 Pierce MT, Crain L, Smith J. et al Point-of-Care versus laboratory measurement of the International Normalized Ratio. Am J Health Syst Pharm 2000; 57: 2271-4.
25 Woods K, Douketis JD, Schnurr T. et al Patient preferences for capillary vs. venous INR determination in an anticoagulation clinic: a randomized controlled trial. Thromb Res 2004; 161-5.
26 Tripodi A, Arbini AA, Chantarangkul V. et al Are capillary whole blood coagulation monitors suitable for the control of oral anticoagulant treatment by the international normalized ratio?. Thromb Haemost 1997; 78: 855-8.