Differential Diagnosis of Thrombocytopenia

Initial Diagnostic Steps

The American College of Physicians recommends examining the peripheral blood smear immediately to exclude pseudothrombocytopenia, which occurs in approximately 0.1% of adults due to platelet clumping in EDTA tubes 1
Obtaining a complete blood count with differential is crucial to assess for other cytopenias that narrow the differential diagnosis 1
Evaluating bleeding symptoms, including petechiae, purpura, ecchymosis, mucosal bleeding, and severity of hemorrhage, is essential 1

The International Society on Thrombosis and Haemostasis suggests that bone marrow examination should be performed in patients with persistent thrombocytopenia lasting >6-12 months or those unresponsive to IVIG, but is not required before initiating IVIG therapy 2
A detailed medication history, including heparin, quinidine, sulfonamides, GPIIb-IIIa inhibitors, and chemotherapy agents, is critical to diagnose drug-induced immune thrombocytopenia 3, 1
The 4T score assigns 0-2 points for each of four criteria: thrombocytopenia severity, timing, thrombosis, and other causes, to assess the clinical probability of heparin-induced thrombocytopenia 3, 1

The American Society of Hematology recommends considering antiphospholipid syndrome, thrombotic thrombocytopenic purpura, disseminated intravascular coagulation, and cancer-associated pseudo-HIT in patients with thrombocytopenia and thrombotic complications 3, 1
Measuring D-dimer and fibrinogen assay is essential to diagnose disseminated intravascular coagulation 1

The European Society of Medical Oncology suggests that chemotherapy-induced thrombocytopenia is often transient with predictable nadir 5
Bone marrow infiltration requires bone marrow examination 1
Immune thrombocytopenia secondary to malignancy should be considered in patients with cancer 4

The International Society on Thrombosis and Haemostasis recommends using a bleeding assessment tool to assess symptom severity in patients with suspected inherited platelet function disorders 6
First-step laboratory tests include blood smear for altered platelet size/structure, light transmission aggregometry, and assessment of platelet granule release 6, 1

The Centers for Disease Control and Prevention recommends HIV testing for patients with risk factors 2, 1

The American College of Physicians recommends initial laboratory tests, including complete blood count with differential, peripheral blood smear examination, prothrombin time, and activated partial thromboplastin time 1
Additional tests based on clinical suspicion, such as D-dimer and fibrinogen for suspected DIC, HIV testing, bone marrow examination, HIT antibody testing, antiplatelet antibodies, and liver and renal function tests, should be performed as needed 1, 2, 3