Pharmacology · patient case question
All of the following statements about platelets are true EXCEPT:
Patient case: Choosing and stopping drugs
demo: Series of prescribing decisions
chief: Several patients seen in one session raise questions about antibiotic choice, analgesia and anticoagulation.
history: One patient has a spreading odontogenic infection unresponsive to five days of empirical antibiotics. Another takes rivaroxaban for atrial fibrillation. A third developed a widespread blistering rash and mucosal ulceration a week after starting a new medication.
meds: Varies by patient.
findings: Not applicable.
Show answer and explanation
Correct answer: A. They are derived from coagulation factor VIII
- A. Correct, and this is the exception. Platelets are not derived from factor VIII. They are fragments of megakaryocyte cytoplasm. Factor VIII is a plasma protein of the intrinsic coagulation pathway, deficient in haemophilia A; it circulates bound to von Willebrand factor, which is a separate matter from platelet production.
- B. This is true. Megakaryocytes in the marrow shed cytoplasmic fragments under the influence of thrombopoietin.
- C. This is true. Platelets survive about 7 to 10 days, which is why aspirin's irreversible effect on cyclo-oxygenase lasts for the life of the exposed platelet pool.
- D. This is true, and surgical bleeding risk rises appreciably below about 50,000 per microlitre.
Note: The recall also listed a claim that men have higher platelet counts than women. In fact women tend to have slightly higher counts, so that option is false too. The unambiguous error is the factor VIII derivation.