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Monitoring anticoagulation in patients with an unreliable prothrombin time/international normalized ratio: factor II versus chromogenic factor X testing. Blood Coagul Fibrinolysis 2014 Apr;25(3):232-6



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Scopus ID

2-s2.0-84897474955   11 Citations


The international normalized ratio (INR) can be unreliable in patients with lupus anticoagulants (LACs) or other conditions affecting baseline testing. Alternative methods to assess anticoagulation on warfarin through measures of vitamin K-dependent factor activity by clot based or chromogenic assays may be necessary. In this patient population, the ideal method is unknown. Thirty-six patients stable on warfarin with LAC or unreliable INR testing had an INR, a prothrombin time-based clotting assay for factor II (FII) activity, and a chromogenic assay for factor X (CFX) activity were performed simultaneously. Eighty-nine sets of measurements were obtained of which 83 sets included all three assays. CFX and FII levels were well correlated (r = 0.92) in all patients and in 26 patients with a documented antiphospholipid antibody (r = 0.93). Parallel testing was seen in 99% of FII assays. Sixty-one percent of CFX and 57% of FII were within the therapeutic range. In 32 CFX and FII pairs wherein assessment of anticoagulation was discordant, 16 CFX agreed with INR and 13 FII agreed with INR (McNemar's, χ = 0.14, P = 0.7). The number of times tests were discrepant was not statistically different between CFX and FII (P = 0.36). CFX and FII activity are well correlated in patients that require alternative monitoring of warfarin. Either test can be used in this population.

Author List

Baumann Kreuziger LM, Datta YH, Johnson AD, Zantek ND, Shanley R, Reding MT


Lisa M. Baumann Kreuziger MD Associate Professor in the Medicine department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Blood Coagulation
Blood Coagulation Tests
Drug Monitoring
Factor X
International Normalized Ratio
Middle Aged
Prothrombin Time