Summary
While laboratory monitoring is not required in patients treated with apixaban, a direct
factor-Xa inhibitor, assessment of its concentration is useful in some critical situations.
However, few data are available on its effect on coagulation tests and on the suitability
of anti-Xa assays for its quantification. It was the objective of this study to identify
laboratory tests suitable for apixaban concentration assessment. Coagulation tests
– PT and aPTT- and anti-Xa assays were performed in apixaban-spiked plasma samples.
To evaluate the sensitivity of PT and aPTT to apixaban, we conducted a first monocenter
part, with a wide range of concentrations (50–1,000 ng/ml), a large panel of reagents
(20 reagents), and two coagulometers (STAR®, Stago and ACL TOP®, IL), and a second multicenter part involving 13 laboratories using either a common
PT reagent (RecombiPlastin2G®) or the local PT and aPTT reagents. In the multicentre part, five blinded apixaban-spiked
plasma samples (0/100/200/400/800 ng/ml – checked by HPLC-MS/MS) were used; apixaban
concentrations were measured with three anti-Xa assays, apixaban calibrators and controls
(Stago). PT and aPTT tests using a large panel of reagents displayed a low sensitivity
to a wide range of apixaban concentrations. The concentrations to double PT ranged
from 400 to >1,000 ng/ml with the 10 reagents. With the three anti-Xa assays, interlaboratory
precision and accuracy were below 11% and 12%, respectively. In conclusion, whereas
PT and aPTT tests were not sensitive enough to detect apixaban, the three anti-Xa
assays tested using lyophilised apixaban calibrators and controls allowed to reliably
quantify a wide range of apixaban concentrations.
Keywords
Apixaban - blood coagulation tests - anti-Xa - anticoagulant agents - multicenter
study