From Jennifer Watson, Centracare Health:
Hello, What are your recommendations when an anti factor Xa returns with a value of 0, even after increasing doses several times? Thank you.
Hello, Jennifer, and thank you for this question. Assuming the heparin dosing has been administered correctly, you may be seeing a patient who has acquired, or even congenital, antithrombin deficiency. Most chromogenic anti-Xa heparin assay kits marketed in the US rely on patient antithrombin for an accurate measurement; these indirectly provide a presumptive indication of antithrombin deficiency by returning lower than expected results. Should you choose to back up the assay with a PTT, it is likely to be affected the same way, meaning its result would be shorter than expected. In this case, your physicians, to ensure the heparin therapy is protective, may choose to administer antithrombin concentrate. Thank you for your question, and I invite additional comments from our participants who may have encountered similar situations.