Sunday April 18, 2010


Q: Describe "Peak" and "Trough" Anti-Xa test?

Answer: Anti-Xa tests are sometimes ordered to monitor and adjust Low molecular weight heparin (LMWH) therapy. It may also be use to monitor unfractionated heparin (UFH) concentrations in the blood instead of primary monitoring tool of PTT test.

"Peak" Anti-Xa test: When it is used as a LMWH monitoring tool, anti-Xa is primarily ordered as a “peak” test. It is collected about 4 hours after a LMWH dose is given, when the concentration of LMWH in the blood is expected to be at its highest level.

"Trough" Anti-Xa test: “Trough” anti-Xa tests may also be ordered when it is suspected that a patient may not be clearing the LMWH at a normal rate. Trough tests are collected just prior to the next dose, when heparin concentrations are expected to be at their lowest.