What is the appropriate management for an adult patient with mild eosinophilia and thrombocytosis, with the rest of the CBC panel being within normal limits?

Management of Mild Eosinophilia and Thrombocytosis with Otherwise Normal CBC

For an adult patient with absolute eosinophils of 515 cells/μL (mild eosinophilia) and platelets of 455,000/μL (mild thrombocytosis), with remaining CBC parameters within normal limits, observation with targeted history and selective testing is appropriate, as this degree of elevation rarely indicates serious pathology and does not meet thresholds for urgent intervention. 1

Initial Risk Stratification

Your patient's laboratory values place them in the lowest risk category:

• Eosinophil count of 515 cells/μL represents mild eosinophilia (0.5-1.5 × 10⁹/L), which is most commonly caused by allergic disorders or medications in non-endemic areas 1
• Platelet count of 455,000/μL is minimally elevated and does not approach thresholds requiring intervention (Grade 1 thrombocytopenia management begins at <100,000/μL) 2
• No evidence of end-organ damage based on normal remaining CBC parameters, which is reassuring as urgent evaluation is only needed when eosinophilia presents with symptoms suggesting cardiac, pulmonary, or neurological involvement 1

Essential Clinical History to Obtain

Travel and exposure history is the single most important diagnostic element, as helminth infections account for 19-80% of eosinophilia cases in returning travelers or migrants 1:

• Fresh water exposure in Africa or tropical regions (schistosomiasis risk) 1
• Raw or undercooked meat consumption (tissue-invasive parasites) 1
• Timing of travel relative to eosinophilia onset 1
• Immigration status or residence in endemic areas 1

Medication review to identify drug-induced eosinophilia, as this is a common reversible cause in mild cases 1

Allergic and respiratory symptoms including asthma, atopic dermatitis, seasonal allergies, as allergic disorders are the most common cause of mild eosinophilia in non-endemic areas 1

Gastrointestinal symptoms specifically dysphagia or food impaction, which would warrant endoscopy for eosinophilic esophagitis evaluation 1

Recommended Diagnostic Workup

For Patients WITH Travel History to Endemic Areas:

Immediate parasitic evaluation is mandatory 1:

• Three separate concentrated stool specimens for ova and parasites 1
• Strongyloides serology and culture 1
• Schistosomiasis serology if fresh water exposure in endemic regions 1

Critical pitfall to avoid: Do not assume normal eosinophil counts exclude parasitic infection, as many helminth-infected patients have normal eosinophil counts 1. However, your patient does have mild eosinophilia, making parasitic workup appropriate.

For Patients WITHOUT Travel History:

Conservative approach with selective testing 1:

• Review and potentially discontinue any recently started medications
• Assess for allergic conditions requiring management
• Consider basic allergy evaluation if clinically indicated

Do NOT routinely pursue extensive hematologic workup at this level of eosinophilia, as moderate to severe eosinophilia (≥1.5 × 10⁹/L) requires hematology referral only if persisting >3 months after infectious causes excluded 1

When to Escalate Care

Urgent hematology referral is NOT indicated for your patient's current values, but would be required if 1:

• Eosinophil count reaches ≥1.5 × 10⁹/L and persists >3 months after infectious causes excluded
• Eosinophil count exceeds 5.0 × 10⁹/L at any time
• Any symptoms suggesting end-organ damage develop (cardiac, pulmonary, neurological)

The thrombocytosis in this case is likely reactive to the underlying process causing eosinophilia, as seen in chronic eosinophilic pneumonia where IL-6 and IL-1β secreted by activated eosinophils can stimulate megakaryocyte production 3. This degree of thrombocytosis does not require specific intervention.

Follow-Up Strategy

Repeat CBC in 4-8 weeks to document whether this represents transient or persistent eosinophilia 1:

• If eosinophilia resolves spontaneously, no further workup needed
• If eosinophilia persists but remains <1.5 × 10⁹/L, continue observation with repeat testing every 3 months
• If eosinophilia progresses to ≥1.5 × 10⁹/L, initiate more comprehensive evaluation including hematology referral after 3 months of persistence 1

Monitor for development of symptoms that would trigger immediate evaluation 1:

• Dysphagia or food impaction (requires endoscopy with multiple biopsies) 1
• Respiratory symptoms with infiltrates (requires pulmonary function tests and chest imaging) 1
• Cardiac symptoms (requires ECG, troponin, NT-proBNP, and echocardiography) 1
• Neurological deficits (requires EMG and potential nerve biopsy) 1

Common Pitfalls to Avoid

Do not initiate corticosteroid therapy without first excluding parasitic causes, particularly Strongyloides, as immunosuppression can cause fatal hyperinfection syndrome in infected patients 1

Do not rely solely on peripheral eosinophil counts to assess tissue eosinophilia in conditions like eosinophilic esophagitis, as peripheral eosinophilia occurs in only 10-50% of adults with this condition 1

Do not wait for symptoms to develop before investigating if eosinophilia progresses to moderate-severe levels, as end-organ damage can be subclinical initially 1