Platelet Autoantibody Panel
- Direct Platelet Antibodies
- Platelet-associated Immunoglobulin
Screen for the presence of circulating antibodies to platelets (not bound to the platelet surface), that may be associated with the destruction of platelets.
Autoimmune thrombocytopenic purpura (AITP) occurs when platelet autoantibodies destroy an individual’s platelets, resulting in a persistent thrombocytopenia.1 In children, AITP is usually self-limiting and frequently resolves spontaneously.2 AITP in children is often associated to a transient viral infection. Approximately 15% of childhood AITP cases become chronic.1 AITP in adults often has an insidious onset, resulting in chronic thrombocytopenia that rarely remits spontaneously.1,2 This condition can be idiopathic or, in some cases, associated with another autoimmune condition (ie, SLE) or malignancy.2
This platelet autoantibody panel is designed to detect IgG antibodies that are bound to platelet-specific glycoproteins llb/llla, lb/IX, or la/lla.3 Antibodies directed against endogenous platelet membrane antigens have been associated with AITP by several laboratories.3-8 A recent study reported that testing for platelet-associated antibodies to llb/llIa, lb/lX, and la/lla had a sensitivity of 53% and a specificity of 72% for diagnosing AITP.3 These results are consistent with the findings from previous studies showing sensitivity ranging from 49% to 66% and specificity ranging from 78% to 92% using assays to detect platelet-associated antibodies to platelet-specific glycoproteins llb/llla and lb/lX.4,5
Tests that measure antibodies to specific platelet antigens have been shown to provide clinical information that is superior to older assays that measured total platelet-associated immunoglobulin G; assays that have often been referred to as PAIgG assays.3-9 While PAIgG assays are frequently positive in patients with AITP, they are also often positive in patients with nonimmune thrombocytopenic disorders.5-9 In contrast to the older PAIgG assays, the platelet antigen specific panel has been shown to have a relatively high positive predictive value of 90%;3 however, the platelet antigen specific panel has been shown to have a low negative predictive value of 24%, indicating that a negative value should not be interpreted as ruling out the condition.3
Red-top tube or gel-barrier tube.
Separate serum from red cells. Transfer serum to a plastic transport tube.
Refrigerate for up to 48 hours, freeze if longer storage is needed.
Hemolysis; serum not separated from cells.
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