What is the workup for isolated thrombocytopenia (low platelet count)?

From the Guidelines

The workup for an isolated low platelet count should begin with a thorough history and physical examination, followed by laboratory testing including a complete blood count with peripheral smear, reticulocyte count, and consideration of specific tests based on clinical suspicion, with bone marrow evaluation reserved for cases with abnormalities in initial testing or concern for aplastic anemia 1. The initial evaluation should focus on identifying potential causes of thrombocytopenia, including medication use, recent infections, and family history of autoimmune disorders.

• A complete blood count with peripheral smear is essential to confirm the diagnosis and rule out pseudothrombocytopenia.
• Reticulocyte count and liver function tests can help identify underlying conditions such as bone marrow failure or liver disease.
• Specific tests such as HIV testing, hepatitis serologies, and antinuclear antibodies may be considered based on clinical suspicion.
• Bone marrow evaluation should be reserved for cases with abnormalities in initial testing or concern for aplastic anemia, as it can help diagnose conditions such as immune thrombocytopenia (ITP) or aplastic anemia 1. In cases of severe thrombocytopenia or bleeding, immediate treatment with corticosteroids or intravenous immunoglobulin may be necessary while completing the workup, with platelet transfusions generally reserved for active bleeding or platelet counts below 10,000/μL 1.
• The management of thrombocytopenia depends on the underlying cause, with ITP potentially requiring immunosuppressive therapy, thrombopoietin receptor agonists, or splenectomy in refractory cases.
• Platelet transfusions should be administered to patients with thrombocytopenia resulting from impaired bone marrow function to reduce the risk of hemorrhage when the platelet count falls below a predefined threshold level, which varies according to the patient’s diagnosis, clinical condition, and treatment modality 1.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Isolated Low Platelet Count Workup

• Thrombocytopenia is defined as a platelet count of less than 150 × 10^3 per μL and can occur from decreased platelet production, increased destruction, splenic sequestration, or dilution or clumping 2.
• Patients with a platelet count greater than 50 × 10^3 per μL are generally asymptomatic, while those with platelet counts between 20 and 50 × 10^3 per μL may have mild skin manifestations such as petechiae, purpura, or ecchymosis 2, 3.
• Patients with isolated thrombocytopenia in the absence of systemic illness most likely have immune thrombocytopenia or drug-induced thrombocytopenia 2, 3.

Diagnostic Approach

• The first step in evaluating isolated thrombocytopenia is to exclude pseudothrombocytopenia by collecting blood in a tube containing heparin or sodium citrate and repeating the platelet count 2.
• A history, physical examination, and laboratory studies can differentiate patients who require immediate intervention from those who can be treated in the outpatient setting 3.
• Examination of the blood film is essential in the investigation of any patient with thrombocytopenia, and the context in which thrombocytopenia occurred, its severity, timing, and association with bleeding are important clues to the diagnosis 4.

Management

• Treatment is based on the etiology and, in some cases, treating the secondary cause results in normalization of platelet counts 3.
• Transfusion of platelets is recommended when patients have active hemorrhage or when platelet counts are less than 10 × 10^3 per μL, in addition to treatment (when possible) of underlying causative conditions 2.
• Corticosteroids are considered the standard initial treatment for newly diagnosed immune thrombocytopenia, with subsequent medical therapies including thrombopoietin receptor agonists, rituximab, and fostamatinib 5.