Over 500 Absolute Eosinophils (“Eos”) is considered “high;” work-up is mostly indicated for counts >1500.  The differential can be remembered as NAACP:

  • Neoplasms  — Primary eosinophilic leukemia (extremely high counts), or more commonly the Lymphomas for which the Eos are a marker. 
  • Allergy  —  Eczema; Upper Respiratory Allergies; Drug reactions.
  • Asthma  —  counts usually <1500; if very high, consider Churg-Strauss Syndrome with asthma.
  • Connective Tissue Disorder  —  Just some rare cases of vasculitis; not common rheumatologic diseases like RA or SLE.
  • Parasites  —  Not protozoa (ameba or giardia).  Occurs with Helminths like Strongyloides, Liver flukes, Toxocara, Trichinosis, Echinococcus, and Hookworm (during the tissue phase of lung passage).

As always, there are diseases that don’t fit the paradigm, like some fungal systemic infections, Addison’s, & some HIV-related conditions.

The main work-up is to repeat counts at least 3 times.  Serology for parasites may be useful, but wouldn’t be necessary in the absence of symptoms.  Third-world travelers or immigrants may warrant three stool O&Ps, even if asymptomatic.

If absolute Eos remain persistently >1500 with no explanation, a chest x-ray or even abdominal CT might be indicated to rule-out lymphoma.  Hematology referral comes next, though most patients with high Eos never wind up with a diagnosis.