Which statement best describes the effect of thrombocytopenia on bleeding risk and routine coagulation tests?

• A. Platelet count below threshold increases bleeding risk; PT/aPTT may be normal.
• B. Platelet count below critical threshold increases bleeding risk; PT/aPTT may be normal.
• C. Platelet count below threshold increases bleeding risk; PT/aPTT are always prolonged.
• D. Platelet count below threshold has no effect on bleeding risk; PT/aPTT abnormal.

Answer: (B)

When platelets are reduced, primary hemostasis is impaired because platelets are needed to form the initial plug at a vessel injury. Bleeding risk rises as the platelet count falls, and this becomes especially evident once counts drop to levels where spontaneous bleeding or bleeding with minor trauma is more likely. In clinical practice, many procedures have safety thresholds around 50,000 platelets/µL, with spontaneous mucosal bleeding more common around 20,000–30,000/µL.

Coagulation tests like PT and aPTT evaluate the plasma coagulation cascade (secondary hemostasis) and are not primarily influenced by platelet number. In isolated thrombocytopenia, the clotting factors are usually normal, so PT and aPTT tend to be unaffected. They become prolonged only if there is a concurrent coagulopathy affecting the factors.

Thus, the statement that best fits is that a platelet count below the critical threshold increases bleeding risk, while PT/aPTT may be normal.