White blood cells are your immune system's soldiers. Learn what your WBC count reveals about infection, inflammation, and immune health.
White blood cells (WBCs), also called leukocytes, are the cells of your immune system. They patrol your blood and tissues, seeking out and destroying pathogens like bacteria, viruses, fungi, and parasites.
Unlike red blood cells (which number in the millions per microliter), WBCs are relatively rare — a normal count is only 4,500-11,000 cells per microliter. Despite their small numbers, they're incredibly powerful defenders.
According to the National Library of Medicine, WBC count is one of the most commonly ordered lab tests, providing crucial information about immune function and potential infections.
The "WBC count" is a total of five different cell types, each with specialized roles. A CBC with differential breaks down the count by type:
| Type | Normal % | Function |
|---|---|---|
| Neutrophils | 55-70% | First responders to bacterial infections |
| Lymphocytes | 20-40% | Viral defense, antibody production, immune memory |
| Monocytes | 2-8% | Clean up dead cells, become tissue macrophages |
| Eosinophils | 1-4% | Allergic responses, parasite defense |
| Basophils | 0.5-1% | Allergic reactions, inflammation |
* The differential helps identify whether elevated WBCs are from bacterial infection (neutrophils↑), viral infection (lymphocytes↑), allergies (eosinophils↑), etc.
Healthy immune function with proper infection defense
Slightly low, may be normal for some individuals
Increased infection risk, requires evaluation
Often indicates infection or inflammation
Acute infection, stress response, or blood disorder
Select your WBC value for a detailed explanation of what it means and what to do next.
Leukopenia means your WBC count is below 4,000-4,500/μL. The Mayo Clinic identifies these common causes:
Bone marrow disorders, chemotherapy, radiation, severe infections, nutritional deficiencies (B12, folate, copper), aplastic anemia.
Autoimmune disorders (lupus), medications (antibiotics, anticonvulsants), hypersplenism, severe bacterial infections that "use up" WBCs.
Many viruses temporarily lower WBCs: HIV, hepatitis, EBV (mono), influenza. Counts usually recover in weeks.
Some people of African, Middle Eastern, or Caribbean descent naturally have lower WBC counts without increased infection risk.
Leukocytosis means your WBC count exceeds 11,000/μL. According to StatPearls, the most common causes are:
Bacterial infections typically raise neutrophils. Viral infections often raise lymphocytes. Your body is producing more soldiers to fight.
Inflammatory bowel disease, rheumatoid arthritis, tissue damage, burns, or surgery can all elevate WBCs.
Physical stress (exercise, pain, seizures), emotional stress, or medications (steroids, epinephrine) can cause temporary spikes.
Smoking can chronically elevate WBCs by 25-30%. Obesity is also associated with mild leukocytosis.
Upload your CBC results and monitor WBC trends. See how your immune markers respond to illness and recovery.
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