Learner decision

Use the whole pattern to localize four failure points. Immune thrombocytopenia, abbreviated ITP, is quantitative platelet loss without a primary defect in adhesion or aggregation of surviving platelets. VWD is a VWF-mediated adhesion problem that requires laboratory characterization. Bernard-Soulier syndrome affects GPIb-IX-V and typically combines thrombocytopenia, giant platelets, and reduced ristocetin-induced agglutination.

Glanzmann thrombasthenia affects αIIbβ3, so aggregation to ADP, epinephrine, and collagen is absent while ristocetin-induced agglutination is normal. Thrombin also aggregates through αIIbβ3 but is not part of the routine LTA agonist panel used here. In the guided case, normal count and morphology make Bernard-Soulier syndrome less consistent, while reduced ristocetin makes Glanzmann thrombasthenia less consistent. The preferred action is not to report a subtype from LTA alone. Order the VWF studies that can characterize the VWF-mediated finding.

Sequence also matters. A platelet cannot aggregate through fibrinogen bridging before activation increases αIIbβ3 affinity, and activation follows adhesion to the exposed matrix. Keep the sequence visible when comparing defects. Choose the next test that separates the remaining differential rather than repeating evidence that already agrees.