Understanding Blood Tests: CBC, ESR, and Differential Tests Explained

Differential Count (Part of CBC)

Measures the percentage of each white blood cell (WBC) type:

• Neutrophils – bacterial defense (most abundant).
• Lymphocytes – viral defense, adaptive immunity.
• Eosinophils – parasitic infections, allergies.
• Basophils – allergic responses, histamine release.
• Monocytes – phagocytosis, tissue repair (largest WBC).

Uses: diagnose infections, monitor disease course, identify WBC disorders.

Erythrocyte Sedimentation Rate (ESR)

Measures how quickly red blood cells settle in a tube. Influenced by RBC count, size, and plasma proteins (especially fibrinogen).

Elevated ESR suggests: anemia, chronic inflammation, infection, malignancy.

ESR is nonspecific; used alongside other tests for diagnosis.