The clinical significance of the antiplatelet antibody test based on results for 265 thrombocytopenic patients.

BACKGROUND

The usefulness of measuring antiplatelet antibodies by ELISA or cytofluorimetric techniques for the diagnosis of idiopathic thrombocytopenic purpura is still uncertain.

METHODS

We evaluated the clinical significance of two widely applicable antiplatelet antibody tests for a series of 265 patients evaluated consecutively in our Department for the diagnosis or follow-up of thrombocytopenia. Flow cytofluorimetry was used to measure platelet-associated immunoglobulins (PAIg) and the enzyme-linked immunosorbent assay (ELISA) was used to detect antiplatelet antibodies in patients sera (S-PBIg). The significance of antiplatelet antibody testing was addressed by studying the factors that influence test positivity, the diagnostic value of a positive test and the prognostic implication of a positive test.

RESULTS

The platelet count was found to be strongly associated with positive PAIg or S-PBIg (P < 0.001), while neither splenectomy nor corticosteroid treatment affected PAIg or S-PBIg positivity. Both PAIg and S-PBIg were limited diagnostic value for the differential diagnosis of idiopathic thrombocytopenic purpura (ITP) from secondary thrombocytopenia for patients with platelet counts between 25,000 and 100,000 platelets/microliters, but the percentages of misclassified patients based on only the PAIg or S-PBIg test were 32 and 54%. We found no relationship between PAIg and/or S-PBIg at time of diagnosis and the patient's clinical response to corticosteroid therapy.

CONCLUSIONS

We conclude that antiplatelet antibodies are strongly correlated with platelet counts, discriminate poorly between ITP and secondary thrombocytopenia and have negligible prognostic value. Therefore, we do not recommend performing antiplatelet antibody tests as a routine laboratory test in the diagnostic workup of thrombocytopenia.