Eosinophils, capable of phagocytosis, ingest antigen–antibody complexes and become active in the later stages of inflammation. Eosinophils respond to allergic and parasitic diseases. Eosinophilic granules contain histamine (one-third of all the histamine in the body).

This test is used to diagnose allergic infections, assess severity of infestations with worms and other large parasites, and monitor response to treatment.

Absolute count: 0–0.5 × 10⁹/L

Differential: 0%–3% of total WBC count

1. Obtain a 5-mL blood sample in a lavender-topped tube (with EDTA). Label the specimen with the patient’s name, date and time of collection (e.g., 3:00 p.m.), and test(s) ordered. Place it in a biohazard bag.

2. Perform a total WBC count, make a blood smear, count 100 cells, and report the percentage of eosinophils.

3. Be aware that an absolute eosinophil count is also available. It is done with a special eosinophil stain and manual counting on a hemacytometer. It must be done within 4 hours after collection or, if refrigerated, within 24 hours.

1. Eosinophilia (increased circulating eosinophils) >5% or >500 cells/mm³ or >0.5 × 10⁹/L occurs in:

   1. Allergies, hay fever, asthma

   2. Parasitic disease and trichinosis tapeworm, especially with tissue invasion

   3. Some endocrine disorders, Addison disease, hypopituitarism

   4. Hodgkin disease and myeloproliferative disorders, chronic myeloid leukemia, polycythemia vera

   5. Chronic skin diseases (e.g., pemphigus, eczema, dermatitis herpetiformis)

   6. Systemic eosinophilia associated with pulmonary infiltrates

   7. Some infections (scarlet fever, chorea), convalescent stage of other infections

   8. Familial eosinophilia (rare), hypereosinophilic syndrome

   9. Polyarteritis nodosa, collagen vascular diseases (e.g., SLE), connective tissue disorders

   10. Eosinophilic gastrointestinal diseases (e.g., ulcerative colitis, Crohn disease)

   11. Immunodeficiency disorders (Wiskott–Aldrich syndrome, immunoglobulin A deficiency)

   12. Aspirin sensitivity, allergic drug reactions

   13. Löffler syndrome (related to Ascaris species infestation), tropical eosinophilia (related to filariasis)

   14. Poisons (e.g., black widow spider, phosphorus)

   15. Hypereosinophilic syndrome (>1.5 × 10⁹/L), persistent extreme eosinophilia with eosinophilic infiltration of tissues causing tissue damage and organ dysfunction

       1. Eosinophilic leukemia

       2. Trichinosis invasion

       3. Dermatitis herpetiformis

       4. Idiopathic

2. Eosinopenia (decreased circulating eosinophils) is usually caused by an increased adrenal steroid production that accompanies most conditions of bodily stress and is associated with:

   1. Cushing syndrome (acute adrenal failure): <50/mm³

   2. Use of certain drugs such as ACTH, epinephrine, thyroxine, prostaglandins

   3. Acute bacterial infections with a marked shift to the left (increase in immature leukocytes)

3. Eosinophilic myelocytes are counted separately because they have a greater significance, being found only in leukemia or leukemoid blood pictures.

Pretest Patient Care

1. Explain test purpose and procedure.

2. Refer to standard patient care for hemogram, CBC, and differential count. Also, follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Daily rhythm: Normal eosinophil count is lowest in the morning and then rises from noon until after midnight. For this reason, serial eosinophil counts should be repeated at the same time each day.

2. Stressful situations, such as burns, postoperative states, electroshock, and labor, cause a decreased count.

3. After administration of corticosteroids, eosinophils disappear.

4. see Appendix E for drugs that affect test outcomes.