Evaluation and Management of Thrombocytosis, Eosinophilia, and Low MCHC in a 27-Year-Old Male
This patient requires systematic evaluation for secondary causes of eosinophilia and thrombocytosis, with particular attention to parasitic infections, allergic conditions, and gastrointestinal eosinophilic disorders before considering primary hematologic disease. 1, 2
Initial Assessment Priority
The combination of moderate eosinophilia (573 cells/μL, normal <500) and thrombocytosis (553 × 10³/μL, normal 150-400) requires investigation, though neither value alone suggests immediate end-organ damage risk. 1, 2 The slightly low MCHC (30.3 g/dL, normal 32-36) may indicate iron deficiency or thalassemia trait and should be evaluated separately. 3
Critical History Elements to Obtain
Travel history is essential - particularly to tropical or subtropical regions where helminth infections are endemic, as parasitic infections account for 19-80% of eosinophilia cases in returning travelers. 1, 2
Medication review - any new medications started within the past 6 months, as drug reactions are a common cause of both eosinophilia and thrombocytosis. 1
Gastrointestinal symptoms - specifically dysphagia, food impaction, abdominal pain, nausea, or diarrhea, which may suggest eosinophilic esophagitis or parasitic infection. 1, 2
Allergic history - asthma, allergic rhinitis, atopic dermatitis, as allergic disorders are the most common cause of mild eosinophilia in non-endemic areas. 2
Respiratory symptoms - persistent cough, wheezing, or dyspnea, as chronic eosinophilic pneumonia can cause both eosinophilia and marked thrombocytosis. 4
Diagnostic Testing Algorithm
First-Line Testing
Stool examination - collect 3 separate specimens for ova and parasites to evaluate for helminth infections. 1
Strongyloides serology - essential given the risk of fatal hyperinfection syndrome in immunocompromised states. 1, 2
Serum tryptase and vitamin B12 - elevated levels screen for PDGFRA-associated myeloproliferative neoplasms. 1
Total IgE level - elevated in allergic conditions and lymphocytic variant hypereosinophilic syndrome. 1
Iron studies - to evaluate the low MCHC, including serum iron, TIBC, ferritin, and hemoglobin electrophoresis if thalassemia is suspected. 3
Empiric Treatment Consideration
For returning travelers with asymptomatic eosinophilia, empiric treatment with albendazole 400 mg single dose PLUS ivermectin 200 μg/kg single dose is reasonable while awaiting test results. 1 This approach addresses the most common helminth infections without delaying potentially important therapy.
Management Based on Findings
If Gastrointestinal Symptoms Present
Proton pump inhibitor therapy twice daily for 8-12 weeks is first-line treatment for suspected eosinophilic esophagitis. 1 However, note that peripheral eosinophilia occurs in only 10-50% of adults with eosinophilic esophagitis, so endoscopy with multiple biopsies remains the gold standard if symptoms persist. 5, 2
If No Clear Secondary Cause Identified
Repeat CBC with differential in 4 weeks to determine if eosinophilia and thrombocytosis persist. 1 Transient elevations can occur with acute infections or inflammatory states and do not require extensive workup. 6
Thrombocytosis Management
The platelet count of 553 × 10³/μL is mildly elevated but does not require immediate intervention. 3 Reactive thrombocytosis (secondary to infection, inflammation, or eosinophilia itself) is far more common than primary myeloproliferative disorders in this age group. 7 The thrombocytosis may resolve once the underlying cause of eosinophilia is treated, as demonstrated in cases of chronic eosinophilic pneumonia where both abnormalities resolved with corticosteroid therapy. 4
Indications for Hematology Referral
Immediate hematology referral is indicated if:
- Eosinophilia persists >1500 cells/μL for more than 3 months despite treatment of secondary causes 1, 2
- Signs of end-organ damage develop (cardiac symptoms, pulmonary infiltrates, neurologic deficits, or skin involvement) 1, 2
- Thrombocytosis persists or worsens after treating secondary causes 7
Hematology workup would include:
- Bone marrow biopsy with cytogenetics and FISH for PDGFRA, PDGFRB, FGFR1 rearrangements 1
- Flow cytometry to evaluate for aberrant T-cell populations 1
- Molecular testing for clonal hematopoiesis 1
Critical Pitfalls to Avoid
Do not assume normal eosinophil counts exclude helminth infection - many infected patients have normal eosinophil counts, so clinical suspicion based on travel history remains paramount. 2
Do not attribute thrombocytosis solely to reactive causes without follow-up - while reactive thrombocytosis is most likely, persistent elevation warrants bone marrow evaluation to exclude chronic myeloproliferative disorders, particularly if JAK2V617F or MPLW515L/K mutations are present. 7
Do not delay evaluation if symptoms develop - fever, weight loss, night sweats, chest pain, or neurologic symptoms with eosinophilia require urgent assessment for systemic vasculitis, malignancy, or hypereosinophilic syndrome with end-organ damage. 2
Do not overlook the low MCHC - iron deficiency anemia can coexist with other conditions and may require separate treatment. 3