A platelet aggregation tracing appears to confirm the diagnosis of Glanzmann thrombasthenia in a patient presenting with a platelet disorder. How would these tracings look if they were performed using light transmittance optical density aggregation?

A platelet aggregation tracing appears to confirm the diagnosis of Glanzmann thrombasthenia in a patient presenting with a platelet disorder. How would these tracings look if they were performed using light transmittance optical density aggregation?

• A. Decreased aggregation to ristocetin
• B. Increased aggregation to ristocetin
• C. Normal response for all agonists
• D. Markedly decreased aggregation to epinephrine, ADP and collagen

Answer: (D)

In Glanzmann thrombasthenia, platelets lack functional GPIIb/IIIa, so they cannot bind fibrinogen to form cross-links and aggregate in response to most agonists. In light transmittance aggregometry, healthy platelets clump and the sample clears, producing a rising trace after stimulation. Because the GPIIb/IIIa/fibrinogen bridge is defective in GT, aggregation is severely reduced in response to agonists such as ADP, epinephrine, and collagen, so the trace shows a markedly blunted or almost flat increase in light transmission. Ristocetin-induced aggregation, however, remains normal in GT because that pathway relies on GPIb-vWF binding and does not depend on GPIIb/IIIa. Therefore, the expected tracing for Glanzmann thrombasthenia shows markedly decreased aggregation to epinephrine, ADP, and collagen, with a normal ristocetin response.

In Glanzmann thrombasthenia, platelets lack functional GPIIb/IIIa, so they cannot bind fibrinogen to form cross-links and aggregate in response to most agonists. In light transmittance aggregometry, healthy platelets clump and the sample clears, producing a rising trace after stimulation. Because the GPIIb/IIIa/fibrinogen bridge is defective in GT, aggregation is severely reduced in response to agonists such as ADP, epinephrine, and collagen, so the trace shows a markedly blunted or almost flat increase in light transmission. Ristocetin-induced aggregation, however, remains normal in GT because that pathway relies on GPIb-vWF binding and does not depend on GPIIb/IIIa. Therefore, the expected tracing for Glanzmann thrombasthenia shows markedly decreased aggregation to epinephrine, ADP, and collagen, with a normal ristocetin response.