Which factors affect the accuracy of factor IX assays?

Updated: Feb 04, 2020
  • Author: Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP; Chief Editor: Eric B Staros, MD  more...
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Answer

Answer

Of the more than 100 factor IX gene mutations that have been identified, many cause bleeding diatheses, though some do not give rise to significant symptoms; a few may result in thromboembolism. [15]

Factor IX deficiency does not affect the prothrombin time (PT) appreciably; however, it does prolong the partial thromboplastin time (PTT) when the factor IX level falls to less than 40% of the normal value. [3]

The following factors may decrease the accuracy of the PT [3] :

  • Partial clotting of specimens, resulting from improper mixture of the anticoagulant (3:2 sodium citrate, as per the manufacturer’s blue-top tube)

  • Overfilling or underfilling of test tubes, either of which alters the blood-to-anticoagulant ratio (9:1)

  • Analytical errors (eg, lipemic, icteric, or hemolyzed plasma), which may interfere with photoelectric measuring instruments

In a study of the direct oral anticoagulant (DOAC) rivaroxaban, which can falsely lower factor VIII and IX values in hemophilia testing, Favaloro et al found evidence that DOAC-Stop can more effectively neutralize this effect than can andexanet alfa. Of laboratories reporting abnormal factor VIII and IX levels from a pool of rivaroxaban-spiked plasma, 86% and 100% determined that the values for factors VIII and IX, respectively, had been corrected by DOAC-Stop. In contrast, 59% and 18% of laboratories continued to report abnormal results for factors VIII and IX, respectively, in association with andexanet-alfa treatment. [16]


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