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Your WBC is elevated — or low — and you're not sure what that means. White blood cells are your body's defence force. Understanding the count and differential tells you which part of immunity is activated.
Clinical Pathology, Hematology ·
The essentials — before you read the full guide below.
The total count of white blood cells per litre of blood. These are the immune cells that fight infection, cancer, and foreign substances.
4.5–11.0 × 10⁹/L in adults. Slightly higher in newborns and young children. Mild elevation on its own is rarely serious.
Most commonly caused by bacterial infection, stress, or corticosteroids. Rarely indicates leukaemia — but a very high count or abnormal differential warrants investigation.
May result from viral infections, medication side effects (especially chemotherapy), or bone marrow suppression.
Reference Ranges
Use the interactive slider below, or read the range cards for a full clinical breakdown.
Drag to see what your WBC Count (White Blood Cell Count) means
The Science
The WBC count is a total — but your report also shows a differential, breaking it down into 5 types. Each type has a different role in immunity, and the differential often tells a more important story than the total count alone.
The most abundant WBC. First responders to bacterial infection and tissue damage. Elevated in bacterial infections, stress, and steroids. Low in viral illness or chemotherapy.
T-cells and B-cells. Elevated in viral infections (and some leukaemias). The differential lymphocyte count rises sharply in Epstein–Barr virus (glandular fever).
Monocytes clean up debris. Eosinophils combat parasites and drive allergic reactions — elevated in asthma, hay fever, and parasitic infection. Basophils are rare but involved in allergic responses.
When to Test
These are the most common reasons a WBC Count (White Blood Cell Count) test is requested — from symptoms to routine screening.
Elevated WBC with fever strongly suggests bacterial infection. The differential distinguishes bacterial (neutrophilia) from viral (lymphocytosis) causes.
Primary useLow WBC with fatigue may suggest viral illness, B12 deficiency, or, less commonly, bone marrow suppression.
Key symptomThese drugs directly suppress WBC production. Regular counts (sometimes weekly) monitor for dangerous drops in neutrophils.
MonitoringWBC consistently above 20 × 10⁹/L without infection, or an abnormal differential, should prompt blood film review for leukaemia.
Red flagElevated eosinophils (part of WBC differential) suggest allergic conditions or parasitic infection — not visible in total WBC count alone.
Differential useWBC is included in every standard CBC. Establishes a baseline and screens for unexpected immune activation.
ScreeningTesting Schedule
Frequency depends on your current health status and your doctor's guidance.
Included in the standard annual CBC. Useful baseline for future comparison.
Repeated at 24–72 hours in hospitalised patients to track response to antibiotics.
Neutrophil count (part of WBC differential) is monitored to prevent life-threatening neutropenic sepsis.
Leukaemia, lymphoma, and bone marrow conditions require regular WBC monitoring.
If Your Result Is Abnormal
Total WBC is a starting point — always interpret with the differential and clinical context.
Ask which cell type is elevated or low. Neutrophilia points to bacterial infection; lymphocytosis to viral. This changes management entirely.
Always check differentialWhen WBC is very high or the differential is abnormal, a blood film reviewed by a haematologist can identify blasts (leukaemia) or atypical cells.
WBC >20 or abnormal diffCRP and procalcitonin help confirm whether an elevated WBC reflects true infection versus steroids or physiological stress.
Confirm infection causePersistent unexplained leukocytosis or leukopenia, or any blood film showing abnormal cells, should be referred to a haematologist promptly.
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