What are the next steps for a 10-year-old patient with low hematocrit (low red blood cell count), normal hemoglobin, normal white blood cell (WBC) count, elevated absolute eosinophil count and elevated absolute basophil count, borderline mean platelet volume (MPV), and normal platelet count?

Diagnostic Workup for Eosinophilia and Basophilia in a 10-Year-Old

Your immediate next step is to obtain a peripheral blood smear to evaluate white blood cell morphology and maturity, followed by targeted testing for parasitic infections, allergic conditions, and consideration of clonal eosinophilia with JAK2 mutation testing if no secondary cause is identified. 1, 2

Initial Laboratory Evaluation

Peripheral Blood Smear (Mandatory First Step)

• Examine for white blood cell maturity, uniformity, and presence of toxic granulations to distinguish reactive from clonal processes 2
• Assess red blood cell morphology to evaluate the discrepancy between low hematocrit and normal hemoglobin (may indicate technical artifact or specific red cell abnormalities) 3
• Evaluate platelet morphology given the borderline mean platelet volume 4

Complete Blood Count Verification

• Repeat the CBC to confirm the eosinophilia and basophilia are sustained findings, as transient elevations can occur with viral infections or stress 2
• Document absolute eosinophil count; sustained elevation ≥1500 cells/μL for at least 6 months defines hypereosinophilic syndrome if organ damage is present 1
• Verify the hematocrit-hemoglobin discrepancy is reproducible 5

Systematic Evaluation for Secondary Eosinophilia

Parasitic Infections (Most Common Cause in Children)

• Obtain stool ova and parasites (3 samples) for tissue-invasive parasites 1
• Consider serologic testing for strongyloides, toxocara, and other endemic parasites based on exposure history 1
• Eosinophilia with parasitic infections specifically occurs with tissue-invasive phases 3

Allergic and Inflammatory Conditions

• Evaluate for asthma, atopic dermatitis, drug reactions, and allergic rhinitis 1
• Consider inflammatory bowel disease if gastrointestinal symptoms are present 2

Medication Review

• Identify any medications that could cause eosinophilia (antibiotics, anticonvulsants, NSAIDs) 2

Evaluation for Primary (Clonal) Eosinophilia

When to Suspect Clonal Disease

• If no secondary cause is identified after thorough evaluation 1
• Presence of concurrent basophilia increases suspicion for myeloproliferative disorder 1
• Any symptoms suggesting hematologic malignancy: fever, weight loss, bruising, fatigue, or splenomegaly 2

Molecular and Cytogenetic Testing

• JAK2 V617F mutation testing should be performed if clonal eosinophilia is suspected, as this identifies imatinib-sensitive molecular targets 1
• Test for PDGFR-alpha and PDGFR-beta gene rearrangements, which predict response to imatinib therapy 1
• These tests are critical because they directly impact treatment decisions 1

Addressing the Hematocrit-Hemoglobin Discrepancy

Technical and Physiologic Considerations

• Low hematocrit with normal hemoglobin is unusual and may represent:
  • Laboratory artifact or specimen handling issue (most common) 5
  • Mild dehydration affecting hematocrit measurement 6
  • Early bone marrow process affecting red cell production 5

Additional Testing if Discrepancy Persists

• Reticulocyte count to assess bone marrow response 3, 5
• Iron studies (ferritin, transferrin saturation, serum iron) to exclude iron deficiency 3, 5
• Mean corpuscular volume (MCV) to characterize any anemia 3

Borderline Mean Platelet Volume Interpretation

Clinical Significance

• Borderline MPV with normal platelet count is generally not concerning in isolation 4
• Low MPV would suggest bone marrow hypoplasia, sepsis, or myelosuppressive drugs, but your patient has normal platelet count 4, 7
• High MPV would suggest hyperdestructive processes or myeloproliferative disorders 4, 7

Critical Red Flags Requiring Urgent Hematology Referral

• Presence of immature white blood cells (blasts) on peripheral smear 2
• Progressive cytopenias on repeat CBC 5
• Splenomegaly or lymphadenopathy on examination 2
• Constitutional symptoms (fever, weight loss, night sweats) 2
• Absolute eosinophil count >1500 cells/μL with any organ symptoms (cardiac, pulmonary, neurologic, or skin involvement) 1

Common Pitfalls to Avoid

• Do not dismiss eosinophilia as "reactive" without systematic evaluation for parasites and allergic conditions 1
• Do not delay JAK2 testing if no secondary cause is found, as clonal eosinophilia requires different management 1
• Do not ignore the concurrent basophilia, as dual elevation increases concern for myeloproliferative process 1
• Do not assume the hematocrit-hemoglobin discrepancy is artifact without verification 5

Timeline for Evaluation

• Peripheral smear and repeat CBC: within 1 week 2
• Stool studies and basic secondary cause evaluation: within 2 weeks 1
• JAK2 and molecular testing if indicated: within 2-4 weeks 1
• Hematology referral if diagnosis uncertain or clonal disease suspected: within 4 weeks 2