Which laboratory test would be most useful to screen for a qualitative platelet defect in a child presenting with mucocutaneous bleeding?

Which laboratory test would be most useful to screen for a qualitative platelet defect in a child presenting with mucocutaneous bleeding?

• A. PT
• B. aPTT
• C. PFA-100 EPI/COLL
• D. TT

Answer: (C)

Qualitative platelet defects alter how platelets respond to injury, so the most informative screening tests focus on platelet function rather than coagulation factor pathways. The PFA-100 uses a collagen surface to trigger platelet adhesion and aggregation under shear, with cartridges that include collagen/epinephrine or collagen/ADP. The time it takes for a platelet plug to occlude the aperture (closure time) increases if platelets don’t function properly or if von Willebrand factor is deficient, making this test a sensitive screen for platelet function abnormalities. In a child with mucocutaneous bleeding, this initial screen is more informative than coagulation tests alone. The other tests assess different parts of the coagulation cascade: PT evaluates the extrinsic pathway, aPTT the intrinsic pathway, and TT the conversion of fibrinogen to fibrin. These would be normal in isolated qualitative platelet defects and do not directly reveal platelet function issues.

Qualitative platelet defects alter how platelets respond to injury, so the most informative screening tests focus on platelet function rather than coagulation factor pathways. The PFA-100 uses a collagen surface to trigger platelet adhesion and aggregation under shear, with cartridges that include collagen/epinephrine or collagen/ADP. The time it takes for a platelet plug to occlude the aperture (closure time) increases if platelets don’t function properly or if von Willebrand factor is deficient, making this test a sensitive screen for platelet function abnormalities. In a child with mucocutaneous bleeding, this initial screen is more informative than coagulation tests alone.

The other tests assess different parts of the coagulation cascade: PT evaluates the extrinsic pathway, aPTT the intrinsic pathway, and TT the conversion of fibrinogen to fibrin. These would be normal in isolated qualitative platelet defects and do not directly reveal platelet function issues.