Laboratory testing

A diagnosis of ITP is made by ruling out other possible causes for low blood platelet counts. To rule out other causes, it is necessary to closely investigate the relevant history of both the patient and family members, perform a physical examination and carry out laboratory tests.

Laboratory testing includes a platelet count, a differentiation of the white blood cells and a mean platelet volume. This often includes testing for viral infections such as HIV and HCV (Hepatitis C Virus) and for the presence of a stomach bacteria (Helicobacter Pylori). The presence of antiphospholipid antibodies can also be excluded.

Performing a platelet antibody test is not part of the standard ITP examination, but it can be requested if there are difficulties in ruling out other causes. Up until recently, research into the presence of autoantibodies against platelets has not been sufficiently specific. Fortunately, the antibody test has now been greatly improved and it is currently being investigated whether it can be included in the routine diagnosis of ITP.

Sometimes there is a problem with counting platelets because they bind to each other or to white blood cells. This phenomenon is called pseudothrombocytopenia and manifests itself at low platelet counts and when the count is performed by automated laboratory machines."

Therefore, it is necessary to count the number of platelets by hand before diagnosing ITP.

If the patient is under six months old, an inherited disorder or a transfer of antibodies from the mother to the child should also be considered.

Bone marrow testing

A bone marrow biopsy and bone marrow aspirate/smear to determine whether the platelet deficiency is due to reduced production or bone marrow displacement by (pre)malignancy, such as myelodysplasia, non-Hodgkin lymphoma or metastasis, rather than increased breakdown may be considered;

• In patients older than 60 years
• Before removal of the spleen
• In therapy resistant patients
• In patients with abnormal physical symptoms or abnormal laboratory results.

Example of the detection of autoantibodies

If autoantibodies are bound to platelets, this can be detected using fluorescence techniques. Nowadays, autoantibody testing is performed using more modern techniques.