[Detection of platelet specific antibodies by modified antigen capture ELISA test.]

Autoimmune thrombocytopenia (AITP) is characterized by autoantibody-induced platelet destruction. Although several studies have shown that pathogenic autoantibodies are mainly IgG directed platelet glycoproteins (GP), a platelet GP specific test is not available in clinical laboratories. The aim of this study was to evaluate the clinical usefulness of a Modified Antigen Capture Enzyme-linked immunosorbent assay (MACE) test in the diagnosis of AITP.

We investigated fifty-seven patients who showed a platelet count lower than 100 x 10(9)/L and underwent a bone marrow examination. They were classified into primary AITP (P-AITP) (n=21), secondary AITP (S-AITP) (n=15), and non-immune thrombocytopenia (NITP) (n=21) by bone marrow findings and clinical diagnosis. Platelet GP (IIb/IIIa, Ia/IIa, Ib/IX, IV)-specific antibodies and anti-HLA class I antibody were detected by MACE test.

Among 57 samples, platelet GP specific antibodies were detected in 8 (22.2%) of 36 patients with AITP and 1 (4.8%) of 21 patients with NITP. The specificities were as follows: GP IIb/IIIa (n=4), GP Ia/IIa (n=5), GP Ib/IX (n=3) and GPIV (n=2). Of the nine patients with platelet GP specific antibodies, four (44.4%) had more than two platelet GP specific antibodies. The sensitivity, specificity, positive predictive value and negative predictive values of the MACE test for AITP were 22.2%, 95.2%, 88.9%, 41.7%, respectively. A previous transfusion history was associated with a higher detection rate of anti-HLA class I antibodies (P<0.05).

The MACE test is a convenient method to detect platelet GP specific antibody and is very specific to diagnose AITP. In clinical practice, even though it is not sensitive, the MACE test would be useful in differentiating AITP from NITP.