ITP Diagnosis Without Antiplatelet Antibody Test?

I met with a hematologist in January and his diagnosis based on my blood count and differentials was ITP. I mentioned that I thought ITP was a diagnosis of exclusion and he shrugged his shoulders. I asked him about the antiplatelet antibody test and he said it wasn't necessary to confirm ITP in my case. Has anyone else been diagnosed with ITP based solely on a CBC and without any further testing? My platelet count was between 62 and 64 in three tests over a two month period.

Thank you!

Yes, most people are usually diagnosed with ITP based on the CBC only. If the rest of the CBC is fine and the patient has no physical symptoms, the default diagnosis is ITP. Anti-platelet antibodies are not normally tested. Some people have ITP with no detectable antibodies, so it's more complicated than it appears. I did have the test at one point which showed a high presence of antibodies but that information never made a difference in treatment of course of the disorder.

Patients over 60 sometimes have a bone marrow biopsy to rule out MDS, but that isn't normally necessary for others unless they do not respond to treatment.

Peripheral blood count

ITP is characterized by isolated thrombocytopenia with an otherwise normal complete blood count. Anemia from blood loss may be present, but it should be proportional to the amount, and the duration, of bleeding and may result in iron deficiency (evidence level IV). If anemia is found, the reticulocyte count may help define whether it the result of poor production or increased destruction of red blood cells (RBCs).

Evaluation of peripheral blood smear

Evaluation of the peripheral blood smear by a qualified hematologist or pathologist is paramount to the diagnosis of ITP. This may demonstrate abnormalities that are not consistent with ITP, such as schistocytes in patients with thrombotic thrombocytopenic purpura–hemolytic uremic syndrome, or leukocyte inclusion bodies in MYH9-related disease. Excessive numbers of giant or small platelets may indicate an inherited thrombocytopenia (supplemental Document 9). Pseudo-thrombocytopenia due to ethylenediaminetetra acetic acid (EDTA)–dependent platelet agglutination should also be excluded14 (evidence level III).


Bone marrow examination

Bone marrow examination may be informative in patients older than 60 years of age, in those with systemic symptoms or abnormal signs, or in some cases in which splenectomy is considered. Both a bone marrow aspirate and a biopsy should be performed. In addition to the morphologic assessment, flow cytometry and cytogenetic testing should be considered (evidence level IIb-IV). Flow cytometry may be particularly helpful in identifying patients with ITP secondary to chronic lymphocytic leukemia (CLL).

Tests of potential utility

Antiplatelet antibody assays: glycoprotein-specific antibody testing.

Assays for antibodies to specific platelet glycoproteins are not routinely recommended because platelet-associated IgG (PaIgG) is elevated in both immune and non-immune thrombocytopenia (evidence level IV).



Diagnostic tests of unproven or uncertain benefit

Several other tests (Table 1) currently have no proven role in the differential diagnosis of ITP from other thrombocytopenias and do not guide patient management.

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