Parameter which should be tested before staing heparin therapy is:-

Bioavailability of unfractionated heparin is inconsistent after SC route and its effect is monitored by testing aPTT (at low doses it selectively affects the intrinsic pathway). LMW heparin and fondaparinux have long half lives and consistent SC absorption; therefore do not require monitoring and once daily SC doses are sufficient. Patients with end stage renal failure and morbid obesity may require monitoring with anti-factor Xa assay.