Role of eosinophils in the differential blood count
The differential leukocyte count represents the percentage ratio of individual leukocyte forms in peripheral blood. This system responds to various homeostatic changes, primarily inflammatory processes, significantly faster than the total leukocyte count changes. Normally, the total leukocyte count is approximately 4–9×10⁹/L. Any deviations from this range are defined as leukocytosis (elevation) or leukopenia (reduction).
When evaluating eosinophil levels, as with other blood cells, it is critically important to analyze not only their relative count (in percentages), but also their absolute values. If the absolute cell count drops below the lower limit of normal, it indicates an absolute deficiency of this cell pool, even if their relative percentage visually remains within normal ranges.
In clinical practice, combined changes in parameters are frequently observed. One such variant is neutrophil-eosinophil leukocytosis. This condition presents with a simultaneous increase in the total leukocyte count, accompanied by both absolute neutrophilia and absolute eosinophilia. Additionally, the analysis may reveal the complete absence of these cells—aneosinophilia—which also warrants close attention when evaluating the overall clinical significance of differential count shifts.
Eosinophilia as a marker of parasitic infections
Detecting eosinophilia in a complete blood count plays a crucial role in diagnosing soil-transmitted helminthiases (e.g., infection with roundworms such as Ascaris). An elevated level of these cells indicates pronounced systemic sensitization, which is characteristic of the parasite's migration phase.
During this period, the clinical picture may be supplemented by physical examination findings:
- Skin: patients frequently exhibit signs of recent infection, such as urticarial exanthema, severe pruritus, and angioedema.
- Respiratory system: auscultation and percussion may reveal localized dullness, harsh or decreased breath sounds, as well as dry and moist rales.
- Abdominal organs: abdominal palpation reveals tenderness in the periumbilical region.
In addition to detecting eosinophilia, diagnosing the intestinal phase involves stool microscopy for helminth ova, while suspected respiratory tract involvement with a cough warrants sputum microscopy. Serological diagnostics (blood ELISA) is used as a screening method, but a positive result alone is not sufficient for a definitive diagnosis due to the risk of false-positive reactions.
Eosinophilia in adverse drug reactions
Careful monitoring of the patient's condition during treatment includes identifying early signs of pharmacotherapy complications. Laboratory monitoring, including complete blood and urine counts every 4–5 days, helps detect pathological shifts in time.
Eosinophilia is one of the key hematological signs of developing complications, along with leukopenia and anemia. Specifically, a sharp increase in eosinophil levels is considered an important laboratory marker of DRESS syndrome in severe drug-induced injuries (combined with leukocytosis and the appearance of atypical lymphocytes).
Skin changes in the form of a rash may also indicate an allergic reaction during therapy (e.g., in the treatment of purulent-inflammatory diseases). At the same time, criteria for the efficacy and safety of the therapy include favorable blood dynamics (normalization of the differential leukocyte count, reduction of leukocytosis and ESR) and normalization of the patient's body temperature.
When evaluating the differential blood count, always remember the "Absolute" rule: a normal percentage does not rule out absolute cell deficiency; calculate absolute values in ×10⁹/L.
Class and exam questions
What does the appearance of eosinophilia mean in a patient with suspected helminthiasis?
Eosinophilia in a complete blood count indicates sensitization (allergic remodeling) of the body, which is particularly characteristic of the roundworm migration phase.
What is the essence of neutrophil-eosinophil leukocytosis?
This is a combined blood abnormality characterized by an elevated total leukocyte count along with an absolute increase in the number of neutrophils and eosinophils.
Eosinophilia serves as a marker for which dangerous adverse drug reaction?
Eosinophilia, alongside leukocytosis and the detection of atypical lymphocytes, is a characteristic marker of DRESS syndrome—a severe systemic reaction to medications.
What else to study on this topic
- Criteria for systemic inflammation: leukocytosis and left shift
- Leukemoid reactions and their distinction from true leukemia
- Diagnostic significance of absolute and relative lymphopenia
- Microscopic and serological methods for diagnosing soil-transmitted helminths
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