In Glanzmann thrombasthenia, which statement about ristocetin-induced aggregation is true?

In Glanzmann thrombasthenia, which statement about ristocetin-induced aggregation is true?

• A. Ristocetin-induced aggregation is normal
• B. ADP-induced aggregation markedly decreased
• C. Epinephrine-induced aggregation markedly decreased
• D. Collagen-induced aggregation markedly decreased

Answer: (A)

Ristocetin-induced aggregation tests the interaction between von Willebrand factor and the platelet GPIb-IX-V complex, a pathway that does not require the GP IIb/IIIa receptor. In Glanzmann thrombasthenia, the GP IIb/IIIa receptor is defective, so platelet aggregation in response to most agonists (like ADP, epinephrine, and collagen) is impaired because fibrinogen bridging cannot occur. However, because ristocetin acts through the GPIb-vWF axis rather than GP IIb/IIIa, the ristocetin-induced aggregation remains normal. This distinction also helps separate Glanzmann from Bernard-Soulier syndrome, where GPIb is defective and ristocetin-induced aggregation is abnormal. So the statement that ristocetin-induced aggregation is normal best fits Glanzmann thrombasthenia.

Ristocetin-induced aggregation tests the interaction between von Willebrand factor and the platelet GPIb-IX-V complex, a pathway that does not require the GP IIb/IIIa receptor. In Glanzmann thrombasthenia, the GP IIb/IIIa receptor is defective, so platelet aggregation in response to most agonists (like ADP, epinephrine, and collagen) is impaired because fibrinogen bridging cannot occur. However, because ristocetin acts through the GPIb-vWF axis rather than GP IIb/IIIa, the ristocetin-induced aggregation remains normal. This distinction also helps separate Glanzmann from Bernard-Soulier syndrome, where GPIb is defective and ristocetin-induced aggregation is abnormal. So the statement that ristocetin-induced aggregation is normal best fits Glanzmann thrombasthenia.