What is the likely diagnosis and recommended work‑up for an 11‑year‑old boy with pallor, generalized body aches and a complete blood count showing neutrophilia, monocytosis and mild eosinophilia?

Likely Diagnosis and Recommended Work-Up

This 11-year-old boy with pallor, body aches, neutrophilia (8179/µL), monocytosis (1331/µL), and mild eosinophilia (563/µL) requires immediate evaluation for serious bacterial infection, hematologic malignancy, or parasitic infection, with priority given to excluding acute leukemia and infectious causes.

Immediate Assessment Priority

The combination of pallor (suggesting anemia) with leukocytosis and multiple elevated cell lines raises concern for:

• Hematologic malignancy – The presence of anemia alongside neutrophilia and monocytosis should prompt evaluation for underlying hematologic disorders 1. Progressive neutrophilia with other cytopenias raises concern for hematologic malignancy and warrants immediate evaluation 1.

• Serious bacterial infection – Neutrophilia with body aches and pallor may indicate systemic infection requiring urgent workup 2.

• Parasitic infection – Eosinophilia (even mild) with systemic symptoms requires consideration of helminth infections, which account for 19-80% of eosinophilia cases in endemic-exposed patients 3.

Critical Initial Workup

Complete Blood Count Analysis

• Obtain complete CBC with differential and reticulocyte count to assess for anemia severity, evaluate all cell lines, and determine if neutrophilia is reactive or concerning for malignancy 4, 1.

• Examine peripheral blood smear to evaluate white blood cell morphology, maturity, presence of blasts, toxic granulations, and uniformity of cells 5. This is essential to differentiate reactive leukocytosis from leukemia 6.

• Assess for "left shift" (immature neutrophil forms) which suggests infection or inflammation versus presence of blasts suggesting acute leukemia 6.

Immediate Red Flag Screening

If any of the following are present, urgent hematology/oncology referral is mandatory:

• Weight loss, bruising, bleeding, or severe fatigue suggesting hematologic malignancy 5, 6
• Hepatosplenomegaly or lymphadenopathy on examination 4
• Blast cells on peripheral smear 4
• Severe anemia (hemoglobin <7 g/dL) or thrombocytopenia 4

Infection Workup

• Obtain detailed travel history to exclude helminth infections, as this is the leading cause of eosinophilia in endemic-exposed patients 3.

• Three separate concentrated stool specimens for ova and parasites if any travel history to endemic regions 3.

• Blood cultures, urinalysis with culture to evaluate for serious bacterial infection given neutrophilia and systemic symptoms 2.

• CRP and/or IL-6 levels – These have higher diagnostic value than WBC count alone for predicting serious bacterial infection, with CRP ≥10 mg/L having 81.6% sensitivity and 89.8% specificity 2.

Bone Marrow Evaluation Indications

Bone marrow aspiration and biopsy are indicated if: 4

• Peripheral smear shows blasts or abnormal cells
• Unexplained persistent cytopenias alongside leukocytosis
• Clinical features suggest primary bone marrow disorder (hepatosplenomegaly, lymphadenopathy, weight loss, bruising)
• Failure to identify reactive cause after initial workup

The bone marrow should include morphology, cytogenetics (minimum 15 metaphases), FISH if cytogenetics fails, flow cytometry for immunophenotyping, and molecular genetics including BCR::ABL1 fusion transcript analysis 4.

Algorithmic Approach to Diagnosis

Step 1: Rule Out Acute Emergency

• If WBC >100,000/mm³, this represents a medical emergency due to risk of brain infarction and hemorrhage requiring immediate intervention 6.
• If patient appears toxic with high fever, consider hemophagocytic lymphohistiocytosis (HLH) 4.

Step 2: Peripheral Smear Interpretation

• Blasts present → Immediate hematology referral for acute leukemia workup 4, 6
• Toxic granulations, left shift, no blasts → Pursue infectious workup 5, 6
• Mature cells only with eosinophilia → Evaluate for parasitic infection or allergic conditions 3, 7

Step 3: Context-Specific Evaluation

• If travel history positive → Empiric treatment with Albendazole 400 mg single dose plus Ivermectin 200 μg/kg single dose while awaiting stool studies 3
• If no travel history and no infection identified → Repeat CBC in 2-4 weeks to assess for persistence 1
• If cytopenias develop or counts worsen → Urgent hematology referral 4, 1

Common Pitfalls to Avoid

• Do not interpret neutrophilia in isolation – Always consider the entire CBC including hemoglobin, platelets, and other white cell lines 1. The presence of pallor (anemia) is a critical red flag that elevates concern beyond simple reactive neutrophilia.

• Do not delay peripheral smear – This is the single most important test to differentiate benign from malignant causes and must be performed immediately 5, 6.

• Do not assume viral illness – While common in children, the combination of pallor, body aches, and multi-lineage elevation requires exclusion of serious pathology first 5.

• Do not miss parasitic infections – Even mild eosinophilia (563/µL is above normal) warrants travel history and stool studies, as helminth infections are highly treatable causes 3, 7.

Specific Hematology Referral Criteria

Immediate referral required if: 4, 1, 5

• Absolute eosinophil count ≥1.5 × 10⁹/L persisting >3 months after infectious causes excluded
• Any eosinophil count >5.0 × 10⁹/L at any time
• Progressive neutrophilia with concurrent cytopenias
• Peripheral smear shows blasts, abnormal morphology, or immature cells beyond left shift
• Clinical features of bone marrow failure (pallor, bruising, hepatosplenomegaly)

The pallor in this patient is particularly concerning and suggests anemia requiring immediate hemoglobin measurement and reticulocyte count to determine if this represents bone marrow suppression, hemolysis, or chronic disease 4.