With creatinine 2.8 mg/dL in a 66-year-old woman, creatinine clearance is very likely <30 mL/min. IV unfractionated heparin needs no renal dose adjustment, and warfarin (bridged with heparin) is also safe in renal failure. Rivaroxaban and other oral Xa inhibitors need CrCl >30, and LMWH (enoxaparin) is cleared by the kidneys, so it needs caution and dose reduction.