Received 11-13-22: We have an ultracentrifuge in our lab that is used in our chemistry department for lipemic samples. In the coagulation department, we have come across lipemic samples for the Anti-Xa assay. If we ultracentrifuge platelet-poor plasma to limit the PF4 release, what effect could this have on the Anti-Xa assay? Thank you.
Hello, and thank you for your question. I understand you saying that your lab ultracentrifuges PPP to limit PF4 release. This may be unnecessary; the customary approach is to prepare PPP in accordance with lab protocol and separate the plasma to avoid ex vivo platelet secretion of PF4, which can partially neutralize therapeutic heparin.
I’ve sent your lipemia question to four experts and have received the following detailed suggestions:
First, ensure your instructions for use provide a threshold for lipemia interference. If the specimen exceeds the limit…
Plan A: Since ultracentrifugation could affect clotting times, ultracentrifuge the patient’s PPP and two nonlipemic “control” PPP specimens with previously determined anti-Xa heparin results, one at 0.2-0.4 IU/mL, another at 0.6-0.8 IU/mL. Record the control values and compare them to the pre-ultracentrifugation values. If there is no change report the patient specimen result. If the controls show a change, select an alternative assay approach or request a new patient specimen.
Plan B: Dilute the specimen at two different dilutions with normal PPP. If the dilutions fall within the linearity of the assay, multiply the results by their respective dilution factors. Report if the two results are within 10%.
Pan C: Reflex lipemic specimens to a clot-based PTT that is calibrated to heparin levels.
We may receive additional recommendations, so you may want to return to this post from time to time.
Added 11-21-22 from Dave McGlasson: Ultracentrifugation has been shown to shorten clot-based coagulation testing due to the destruction of platelets. I can find nothing however that ridding a sample of lipemia after the PPP has been separated will affect the anti-Xa test for the presence of heparin. I have called two manufacturers’ technical departments and they have no literature or studies that address this issue.