Which statement about unfractionated heparin is true?

• A. It is derived from bovine intestine
• B. It primarily inhibits Factor Xa
• C. It requires permanent renal dose adjustments
• D. It is fully reversible with protamine sulfate

Answer: (D)

Reversibility with a specific antidote is the key idea here. Unfractionated heparin can rapidly neutralize its anticoagulant effects when protamine sulfate is given. Protamine binds to heparin and forms a stable complex that stops its activity, so bleeding can be controlled or surgery can proceed with anticoagulation reversed. The reversal is essentially complete for unfractionated heparin, which is why this statement is true.

To understand why the others aren’t correct: unfractionated heparin is typically derived from porcine intestinal mucosa (not bovine intestine), and it inhibits both thrombin (factor IIa) and factor Xa via antithrombin, not solely factor Xa (that more closely describes LMWH). Its clearance is not primarily renal, so permanent renal dose adjustments aren’t required for UFH. In contrast, protamine neutralizes UFH well, but it doesn’t fully reverse several other anticoagulants such as LMWH or fondaparinux.