Abstract: The present invention is directed to determining the presence of antibodies from a patient's blood which are specific for HLA Class I antigens and/or platelet glycoproteins. The invention provides for a method and kit for diagnosing platelet disorders in an easy to use format. The method and kit employ a solid support, such as microtiter plate wells, that are coated with the HLA and glycoprotein antigens. A sample of the patient's blood is added to the coated wells and allowed to react, then spectrophotometric detection of antibodies provides diagnostic quantitation.