This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hematology, Subject name: Pharmacology
Laboratory monitoring of which of the following is desirable with low molecular weight heparin therapy in a patient with renal failure? 
Select and explain. 
A. aPTT, B. CT, C. PT, D. Anti-factor Xa activity
D: Anti-factor Xa activity
Answer: D: Anti-factor Xa activity 
Explanation: 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.