Evaluation of Elevated White Cell Count in a 17-Year-Old Male
A complete blood count with differential is the essential first test, followed by peripheral blood smear examination to characterize the leukocytosis and guide further workup based on the differential pattern and clinical context. 1
Initial Laboratory Assessment
The foundational workup begins with:
- CBC with differential and peripheral blood smear to determine which white cell lineage is elevated (neutrophils, lymphocytes, eosinophils, monocytes, or basophils) and assess cell maturity 2, 1
- Comprehensive metabolic panel including liver function tests, renal function, electrolytes, and lactate dehydrogenase 2
- Review of peripheral smear for cell morphology, presence of immature forms ("left shift"), toxic granulations, or abnormal cells 1, 3
The differential pattern determines the diagnostic pathway. An elevated WBC count (>14,000 cells/mm³) or left shift (band neutrophils ≥6% or >1,500/mm³) warrants careful assessment for bacterial infection 2.
Context-Dependent Additional Testing
If Neutrophilic Leukocytosis Predominates:
- Inflammatory markers: ESR and CRP to assess for infection or inflammatory conditions 2
- Blood cultures if fever or signs of systemic infection are present 2
- Urinalysis and urine culture if urinary symptoms exist 2
- Consider chest radiograph if respiratory symptoms present 2
If Lymphocytosis Predominates:
- Peripheral blood immunophenotyping by flow cytometry (CD19, CD20, CD5, CD10, CD23) to evaluate for lymphoproliferative disorders 2
- Serum protein electrophoresis and immunofixation if lymphoplasmacytic infiltrate suspected 2
- Infectious workup including EBV, CMV serology for reactive lymphocytosis 1
If Eosinophilia Predominates:
- Serum IgE level 2
- Serum tryptase and vitamin B12 (elevated in myeloproliferative variants) 2
- Stool ova and parasites, serology for Strongyloides and other parasitic infections 2
- Bone marrow aspirate and biopsy with cytogenetics and molecular testing for tyrosine kinase fusion genes if primary eosinophilia suspected 2
Red Flags Requiring Urgent Hematology Referral
Immediate hematology/oncology consultation is indicated if: 1, 3
- WBC count >100,000/mm³ (medical emergency due to hyperviscosity risk) 3
- Presence of circulating blasts or immature cells on peripheral smear 2
- Concurrent unexplained anemia or thrombocytopenia 2
- Constitutional symptoms: fever, night sweats, weight loss, fatigue 1
- Hepatosplenomegaly or lymphadenopathy on examination 2, 1
- Abnormal cell morphology suggesting dysplasia 2
Bone Marrow Evaluation Indications
Bone marrow aspirate and biopsy with comprehensive testing should be performed when: 2
- Malignancy cannot be excluded based on peripheral blood findings 1
- Persistent unexplained leukocytosis after excluding reactive causes 1, 3
- Abnormal immunophenotype on flow cytometry 2
- Multiple cell line abnormalities present 2
The bone marrow workup should include: conventional cytogenetics, FISH for specific translocations (particularly BCR-ABL1, MLL rearrangements), immunohistochemistry, and flow cytometry 2. For suspected acute lymphoblastic leukemia, HLA typing should be performed at initial workup 2.
Common Pitfalls to Avoid
- Do not assume infection solely based on elevated WBC - physical stress, medications (corticosteroids, lithium, beta-agonists), smoking, and obesity can all cause leukocytosis 1, 3
- Do not delay referral when peripheral smear shows immature cells or blasts - this requires urgent evaluation regardless of absolute WBC count 2, 1
- Do not order bone marrow biopsy before completing peripheral blood evaluation with differential and smear review 1
- In renal colic with elevated WBC, antibiotics are not indicated unless urinalysis shows pyuria/nitrites or patient has fever - leukocytosis alone is common and non-infectious 4
The age of 17 years places this patient in an intermediate risk category where both pediatric-type ALL (with better prognosis) and adult-type leukemias can occur, making thorough initial characterization particularly important 2.