Platelet glycoprotein autoantibodies (GP IIb/IIIa, Ib/IX, Ia/IIa)

This Quest Diagnostics panel looks for autoantibodies against specific proteins on the surface of your own platelets. It is mainly used when doctors are investigating immune thrombocytopenia (ITP), a condition in which the immune system destroys platelets.

The three platelet proteins tested:

• GP IIb/IIIa: the most common target of platelet autoantibodies.
• GP Ib/IX: the receptor that helps platelets stick to damaged blood vessel walls.
• GP Ia/IIa: a receptor that helps platelets bind to collagen.

The two sample types:

• Eluate results: antibodies washed off your own platelets. This shows antibodies already bound to them (a direct test).
• Plasma results: antibodies circulating freely in the plasma (an indirect test).

How to read the results:

• A positive eluate result supports an immune cause of a low platelet count.
• A negative result does not rule out ITP. Many people with ITP test negative, so ITP is still diagnosed mainly by excluding other causes.
• Positive results can also appear with some medicines, infections and other autoimmune conditions.

Hematology guidelines do not recommend this test routinely, but it can help in unclear cases.