April 2022 QQ: Measuring Heparin Summary

Hello, our April 2022 Quick Question asks, “How do you measure unfractionated heparin [UFH]?” Our 37 respondents answered…

1. Chromogenic anti-Xa using a hybrid curve: 38% [14]
2. Chromogenic anti-Xa using the UFH curve: 14% [5]
3. Anti-Xa and PTT: 22% [8]
4. PTT: 26% [9]

The majority of respondents are using the chromogenic anti-Xa heparin assay, and most have adopted the hybrid curve, enabling them to measure both UFH and low molecular weight heparin [LMWH] using a single curve. Many of us continue to use the PTT. The PTT remains an acceptable means for monitoring UFH if it is calibrated to the chromogenic anti-Xa heparin assay using the ex-vivo “Brill-Edwards” curve.

Answer 3 raises the issue addressed in the article below. Although we offer the more accurate and reproducible chromogenic anti-Xa heparin assay, our menu still offers the PTT, the primary means to detect intrinsic pathway coagulopathies such as factor VIII or factor IX deficiency. Consequently, physicians may compare the anti-Xa heparin assay results to PTT results and find discrepancies, a concern addressed in this article from the Laboratory Medicine staff at the University of Alabama at Birmingham:

May JE, Siniard RC, Taylor LJ, Marques MB, Gangaraju R. From activated partial thromboplastin time to antifactor Xa and back again; the evolution of monitoring unfractionated heparin. Am J Clin Pathol 2021: HTTPS://DOI.ORG/10.1093/AJCP/AQAB135