Anti-Xa and Lipemia

From “McDowekm:”

We currently perform anti-Xa heparin testing on a hybrid curve using Stago’s Rotachrom reagent on our Stago Compact. If we have a specimen that is lipemic, it can falsely increase the anti-Xa result. Can these specimens be ultra-centrifuged to obtain a more accurate Anti-Xa result?

Hello and thank you for your question. It would be helpful to review your data that indicate lipemia is raising your anti-Xa results. When performing the Rotachrom assay according to published protocols using the hybrid curve, the original specimen reaches a final dilution, counting diluents and reagents, of 1:22. Given this dilution, and according to the manufacturer’s package insert, interference will occur only when the original triglyceride concentration rises to above 360 mg/dL. Also, because the color intensity of the reaction is inversely proportional to heparin concentration, lipemia would be expected to reduce, not raise the anti-Xa result. Your data could substantially support or refute these claims.

I received some help on this question from Dave McGlasson at Wilford Hall USAF Medical Center in San Antonio, and he made an interesting observation about ultra-centrifugation. Ultra-centrifugation activates platelets, causing them to release platelet factor 4 (PF4), which neutralizes heparin. Thus, ultra-centrifugation of specimens for heparin assay is likely to falsely reduce heparin results. I hope this is helpful. Geo.