No diagnostic assay with a high predictive value has yet been developed for ITP.¹ According to current guidelines, the diagnosis of ITP remains one of exclusion. A diagnosis of exclusion presents many difficulties to the clinician. Therefore, several attempts have been made to develop a sensitive and specific test that would enable direct laboratory confirmation of ITP. Current assays are based on the measurement of platelet-glycoprotein–specific autoantibodies. However, the sensitivity (49% to 66%) of these assays is not high enough to exclude the diagnosis of ITP when results are negative and the specificity is also not sufficient to confirm the diagnosis of ITP.²