White blood cells

Laboratory parameters and pathogen counting

In clinical practice, evaluating the leukocyte count is inextricably linked with the analysis of other blood parameters. In particular, a complete blood count (CBC) helps identify complex changes accompanying the infectious process. Against the background of a leukocyte count of 10×10⁹/L, a pronounced decrease in hemoglobin (Hb) down to 95 g/L may be observed, indicating the development of anemic syndrome. Simultaneously, an acceleration of the erythrocyte sedimentation rate (ESR) up to 36 mm/h is recorded, confirming a systemic inflammatory response.

Biochemical blood analysis complements the clinical picture. Patients may exhibit changes in carbohydrate metabolism parameters, for example, a decrease in blood glucose concentration to 3.2 µmol/L.

Microscopic examination A crucial function of leukocytes in the laboratory diagnosis of parasitoses is their use as a reference point for the quantitative assessment of the pathogen. During microscopy of blood smears, parasitemia density is calculated based on the number of microorganisms detected per a specific number of white blood cells. For instance, in Plasmodium falciparum infection, the concentration can reach up to 100 parasites per 10 leukocytes. To accurately determine the severity of the condition, this ratio must be recalculated per 1 microlitre (µL) of the patient's blood.

Clinical presentation against the background of blood changes

Changes in laboratory parameters, including the leukocyte count, are accompanied by characteristic clinical manifestations that vary depending on the pathogen species and disease duration. Patients frequently complain of pronounced fatigue and chills.

Key objective and anamnestic data include:

• Febrile syndrome: Body temperature rises in the evening, reaching 38–38.5°C. The duration of the febrile attack averages 5–6 hours. A specific type of fever is characteristic, in which attacks recur strictly every other day. Patients often use aspirin as a form of self-treatment.
• Abdominal organ changes: Objective status consistently demonstrates involvement of the liver and spleen. Hepatomegaly is observed — the liver is enlarged and extends +1 cm below the costal margin. Splenomegaly is also recorded — palpation reveals a dense or moderately dense edge of the enlarged spleen.
• General condition: During the afebrile period, despite the presence of the infection, the condition may be assessed as satisfactory, and body temperature returns to normal values. The skin maintains its normal coloration.

Epidemiological history and pathogen species

Interpretation of laboratory data, including parasite counts relative to leukocytes, is impossible without a thorough collection of the epidemiological history (Anamnesis epidemica). Identifying the specific species of Plasmodium directly depends on the region of the patient's stay:

1. Indian region: A prolonged stay in India (e.g., for 1 year) is associated with the risk of Plasmodium vivax infection (vivax malaria). The history of such patients often notes treatment with chloroquine, which provides a good clinical effect. However, a critical factor for relapse is the omission of primaquine therapy as part of the regimen. Relapse or manifestation of the disease may occur six months after returning from the assignment.
2. African region: A stay in West Africa (e.g., working at an embassy for 3 years) is associated with the risk of Plasmodium malariae infection. The disease may be latent: after returning, female patients may undergo repeated examinations without recurrent attacks, and parasites in blood smears remain undetected for a long time. Manifestation may recur even 6 years after return.

Impact of comorbid conditions

Assessment of the patient's condition is complicated by the presence of comorbid chronic conditions. An infectious process caused by Plasmodium malariae may develop against the background of severe renal damage, such as chronic glomerulonephritis (with a duration of about 2 years).

In such cases, the clinical and laboratory picture is significantly aggravated:

• The patient's general condition is assessed as moderate severity.
• Massive edematous syndrome develops, progressing up to anasarca.
• Marked hemodynamic disorders are noted, in particular, an increase in blood pressure up to 170/100 mmHg.
• Urinalysis records significant protein loss — proteinuria reaches a level of 2 g/day.

Such complications require a comprehensive approach to formulating the diagnosis, accounting for all developed syndromes, and prescribing the most adequate etiotropic therapy considering the nephrological status.

Class and exam questions

What else to study on this topic

• Methodology for recalculating the parasite count per 1 µL of blood based on the leukocyte level
• Specific etiotropic therapy for malaria depending on the Plasmodium species
• Mechanisms of chronic glomerulonephritis development in Plasmodium malariae infection
• Rationale for selecting additional diagnostic tests to confirm the form of parasitic infection

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.