LMWH preparations are derived from standard porcine heparin by chemical or enzymatic degradation to yield fragments between 1,000 to 10,000 daltons. LMWHs are used for the prevention and treatment of thrombosis. Similar to standard heparin, LMWH preparations produce their major anticoagulant effect by catalyzing Antithrombin. Due to their smaller size (generally less than 18 saccharides), LMWH preparations have a higher anti-Xa to anti-IIa ratio than standard heparin (between 2-4 times more anti-Xa activity). As such LMWH preparations generally do not (or minimally so) prolong the APTT and therefore are monitored, if necessary, by an anti-Xa assay.
