Investigations
1st investigations to order
FBC and peripheral blood smear
Test
Peripheral blood smear distinguishes between true thrombocytopenia and pseudothrombocytopenia (a spuriously low platelet count in blood samples collected into ethylenediaminetetraacetate [EDTA]-containing collection tubes; occurs in about 0.1% of adults; this can be uncovered by a normal platelet count on peripheral blood smear or by using a citrate tube instead of an EDTA tube).
There should be no evidence of myelodysplasia or other disorders (i.e., Pelger-Huet anomaly, nucleated red blood cell, schistocytes, immature granulocytes, large granular lymphocytes). Other cell lines (i.e., red cells and white cells) should be normal.
Result
platelet count <100 × 10⁹/L (<100 × 10³/microlitre)
Investigations to consider
HIV serology
Test
Routine testing for HIV infection is recommended for adult patients to exclude an important differential.[15]
Result
negative
Helicobacter pylori breath test or stool antigen test
Test
Testing for Helicobacter pylori infection (urea breath test or stool antigen tests) is indicated in patients with appropriate risk factors or in high-prevalence areas (e.g., southern and eastern Europe, South America, and Asia).[15][17][18] However, very low platelet counts (i.e., <10 × 10⁹/L (<100 × 10³/microlitre]) are not usually observed in patients with H pylori infection.
Result
negative
hepatitis C serology
Test
Routine testing for hepatitis C infection is recommended for adult patients to exclude an important differential.[15]
Result
negative
thyroid function tests and antithyroid antibody tests
Test
Approximately 8% to 14% of patients with Immune thrombocytopenia develop clinical hyperthyroidism on prolonged follow-up, and patients may develop antibodies to thyroglobulin.
Mild thrombocytopenia has been associated with hyperthyroidism (reduced platelet survival) and hypothyroidism (possible decreased platelet production), which may resolve with restoration of the euthyroid status.[15]
Should be tested before elective splenectomy as it is important to exclude all possible reversible causes of thrombocytopenia before subjecting the patient to the risks of the procedure.
It is not a common enough cause to check on initial laboratory testing if the patient is asymptomatic.
Result
may be hyper- or hypothyroid
quantitative immunoglobulins
Test
Quantitative immunoglobulins level testing is recommended to exclude an immune deficiency syndrome, or before treatment with intravenous immune globulin. In children, it may be considered at baseline and should be measured to re-evaluate persistent or chronic immune thrombocytopenia.[15]
Result
may reveal common variable immunodeficiency or selective IgA deficiency
bone marrow biopsy/aspiration
Test
Only considered if atypical blood film features are present. Not routinely recommended at initial diagnosis, but it may be considered in patients who are unresponsive to medical therapy, or prior to splenectomy.[15]
Result
increased megakaryocytes; no evidence of malignancy; no flow cytometry or cytogenetic abnormalities
pregnancy test
Test
Pregnancy testing should be considered in women of childbearing age. Thrombocytopenia in pregnancy may be due to a pregnancy-related cause, rather than immune thrombocytopenia (ITP).[19] Among other possible causes, gestational thrombocytopenia, hypertensive disorders of pregnancy (e.g., pre-eclampsia or haemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome), and acute fatty liver disease should be considered and excluded. These usually develop in late pregnancy, whereas ITP is the most common cause of thrombocytopenia in early pregnancy. Gestational thrombocytopenia accounts for 70% to 80% of thrombocytopenia in pregnancy.[20]
Result
may be positive or negative
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