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Factor IX level failed to affect INR in patients taking warfarin

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53rd ASH Annual Meeting

SAN DIEGO — The level of Factor IX was linked to thrombin generation but did not affect the international normalized ratio in patients taking warfarin, according to results presented here.

Yesim Dargaud, MD, PhD, of the Clinical Hemostasis Unit of Hopital Edourad Herriot in Lyon, France, said patients with an INR in the target range of 2 to 3 may experience bleeding.

“This indicates that the ratio does not perfectly reflect the therapeutic effect of warfarin,” Dargaud said.

The aim of the prospective, single-center study was to determine whether the level of specific coagulation factors was predictive of bleeding risk when the INR was in the target range.

“We also wanted to determine if there is any relationship between Factor IX levels and the clinical outcome of patients during warfarin therapy,” she said.

A correlation between thrombin generation and INR exists when a range of the ratio is between 1 and 10, according to Dargaud.

The final analysis involved 456 consecutive patients on warfarin with an INR between 1.8 and 3.2. A decrease of Factor IX was linked to a decrease in thrombin generation.

“In a warfarinised plus model, there is no correlation between thrombin generation and INR,” she said. “We also studied the relationship between Factor IX and INR, and found no correlation.”

Variations in the levels of Factor IX could cause the INR to be an imperfect reflection of a patient’s level of anticoagulation when treated with warfarin.

“Our results suggest that the appropriate target INR level might not be the same for all patients,” Dargaud said. “Those with Factor IX levels that differ significantly from the mean of the population might be managed best by selecting a target INR that is based on the level of thrombin generation.”

A target range for parameters of thrombin generation during warfarin therapy may be necessary, she said.

Disclosure: Dr. Dargaud reports no relevant financial disclosures.

For more information:

• Dargaud Y. Abstract #541. Presented at: 53rd Annual Meeting of the American Society of Hematology; Dec. 10-13, 2011; San Diego.

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