Which pattern of aggregation results supports Glanzmann thrombasthenia?

Which pattern of aggregation results supports Glanzmann thrombasthenia?

• A. Abnormal aggregation with all agonists
• B. Absent ristocetin-induced aggregation; normal others
• C. Absent aggregation with ADP, collagen, epinephrine; ristocetin-induced aggregation within reference range
• D. Normal aggregation with all agonists

Answer: (C)

Glanzmann thrombasthenia is due to a defect in the platelet GPIIb/IIIa receptor, which is essential for cross-linking platelets during aggregation by fibrinogen and other ligands after platelet activation. Because of this, aggregations triggered by ADP, collagen, or epinephrine fail to form properly. However, ristocetin-induced aggregation relies on the GPIb-vWF interaction and does not require GPIIb/IIIa, so it remains normal. The pattern described—absent aggregation with ADP, collagen, and epinephrine, with normal ristocetin-induced aggregation—best fits Glanzmann thrombasthenia. This also helps distinguish it from Bernard-Soulier syndrome, where ristocetin-induced aggregation is abnormal due to GPIb defects.

Glanzmann thrombasthenia is due to a defect in the platelet GPIIb/IIIa receptor, which is essential for cross-linking platelets during aggregation by fibrinogen and other ligands after platelet activation. Because of this, aggregations triggered by ADP, collagen, or epinephrine fail to form properly. However, ristocetin-induced aggregation relies on the GPIb-vWF interaction and does not require GPIIb/IIIa, so it remains normal. The pattern described—absent aggregation with ADP, collagen, and epinephrine, with normal ristocetin-induced aggregation—best fits Glanzmann thrombasthenia. This also helps distinguish it from Bernard-Soulier syndrome, where ristocetin-induced aggregation is abnormal due to GPIb defects.