Laboratory Evaluation for Very Low WBC and Platelets

Initial Laboratory Evaluation

The Centers for Disease Control and Prevention recommends a complete blood count with differential and peripheral blood smear examination to confirm true thrombocytopenia and leukopenia, identify potential alternative diagnoses, and assess for abnormal cells 1, 2
Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT) should be evaluated to assess coagulation function, as recommended by the American Society of Hematology 1, 2
D-dimer measurement and fibrinogen assay should be performed to assess for disseminated intravascular coagulation, according to the British Medical Journal 1, 3
Liver function tests should be conducted to rule out liver disease as a cause, as suggested by the National Comprehensive Cancer Network 4, 1
A chemistry profile should be evaluated to assess renal function and nutritional status, as recommended by the Infectious Diseases Society of America 5

The National Comprehensive Cancer Network recommends bone marrow aspiration and biopsy, especially if abnormal cells are seen in peripheral blood or if no obvious cause is identified from initial testing 4, 6
Bone marrow examination should not be delayed in patients with unexplained cytopenias, especially when clinical suspicion for malignancy is high, as advised by the National Comprehensive Cancer Network 4, 6

For hematologic malignancies, flow cytometry of peripheral blood and/or bone marrow should be performed to identify leukemia or lymphoma, as recommended by the National Comprehensive Cancer Network 4, 6
Cytogenetic analysis and molecular studies, including FISH, RT-PCR, and next-generation sequencing, should be conducted to detect genetic abnormalities associated with leukemia, as suggested by the National Comprehensive Cancer Network 4, 6
For immune-mediated causes, anti-platelet antibody testing should be performed if immune thrombocytopenia is suspected, as recommended by the American Society of Hematology 7, 8
For infectious causes, HIV testing should be conducted, as HIV infection can cause both cytopenias, according to the Centers for Disease Control and Prevention 5, 8

If von Willebrand disease is suspected, VWF antigen, VWF ristocetin cofactor activity, and factor VIII coagulant activity should be evaluated, as recommended by the American Society of Hematology 9, 2
For suspected inherited platelet function disorders, light transmission aggregometry with various agonists should be considered, as suggested by the International Society on Thrombosis and Haemostasis 2, 10

The Centers for Disease Control and Prevention advises against assuming that leukopenia and thrombocytopenia are always due to the same cause, as multiple pathologies may coexist 1, 2
The National Comprehensive Cancer Network recommends avoiding delays in bone marrow examination in patients with unexplained cytopenias, especially when clinical suspicion for malignancy is high 4, 6