White Blood Cell Count
White blood cells are your body's defence force against infection, and this count adds up the total in your blood. A result inside the range on your report is reassuring. The number naturally rises when you are fighting something off and settles back once you are better, so a recent cold can nudge it.
Standard CareWhat is white blood cell count?
White blood cells (WBCs) — doctors also call them leucocytes — are part of your immune system. They help your body fight infection and other diseases, including cancer. The WBC count reports the total number of these cells in your blood, expressed as billions of cells per litre (×10⁹/L). A full blood count (FBC) routinely includes both the total WBC count and a differential — a breakdown of that total into the five main types of white cell: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Each type has a distinct role in immunity, and the pattern of which type is elevated or reduced can help your GP identify the likely cause of an abnormal result. The WBC count alone tells you how many immune cells are present; the differential tells you which kinds. Your GP reads them together, alongside haemoglobin, platelets, and your clinical picture.
Why is it tested?
A WBC count is one part of the picture your GP uses to understand your immune system, and whether your bone marrow (the factory that produces white cells) is producing them in normal numbers. Common reasons include: investigating symptoms of infection (fever, persistent illness, unusual fatigue), monitoring a known condition that affects immunity or bone marrow, checking in before or during chemotherapy or immunosuppressive treatment, and as part of a routine full blood count health screen. The full blood count checks different types of blood cells to help find signs of infections, blood disorders, and other health conditions. The WBC count is one component of that broader picture.
Reference range (Australia)
Reference intervals for WBC count are laboratory- and analyser-specific. Age and some other factors can also influence the expected range. The range printed on your pathology report is the correct one to apply to your result.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A low WBC count — doctors call this leucopenia — means fewer immune cells are circulating than expected. The bone marrow can make fewer white blood cells after certain viral infections, with autoimmune conditions, or with bone marrow disorders. Some medicines do it too, including chemotherapy and some anti-thyroid drugs. A mildly low count is often temporary and lifts once the trigger passes. A very low count, particularly of neutrophils (the white cells that tackle bacterial infections first), can reduce the body's ability to fight off bacteria. Your GP will look at the pattern and talk you through what happens next.
A WBC count within the range on your report suggests your immune system is producing white cells in normal numbers. This is reassuring. Keep in mind that the count can fluctuate with the time of day, recent physical activity, and minor illness — a normal result on one test is generally a good sign, and any changes are tracked over time rather than inferred from a single reading.
A raised WBC count — doctors call this leucocytosis — most often means your immune system is actively responding to something. When there is an inflammatory process or infection somewhere in the body, the bone marrow produces more white blood cells and releases them into the circulation, where they travel to the site of inflammation or infection. Common causes of a raised count include a bacterial infection or a viral illness in its early phase. Tissue injury, physical stress, and certain medicines such as corticosteroids (anti-inflammatory steroids like prednisolone) can do it too. A count raised for these reasons typically falls back to normal once the underlying cause settles. A count that stays high, or is markedly raised without an obvious cause, is worth a closer look. Your GP will check the differential to see which type of white cell is elevated and consider whether further investigation is needed.
What can affect your result
Infection and inflammation are the most common drivers of a raised WBC. The bone marrow will produce more white blood cells and release them into the circulation when the body is fighting a bacterial or viral infection, and levels will drop back to normal when the condition resolves. Medicines are an important factor. Corticosteroids (anti-inflammatory steroids such as prednisolone) raise WBC counts by releasing stored neutrophils from the bone marrow. Other medicines can do the reverse and lower the count. These include some anti-thyroid drugs, disease-modifying antirheumatic drugs (DMARDs, used to calm conditions like rheumatoid arthritis), and chemotherapy agents, which can quieten the bone marrow. Physiological stress, including intense exercise and emotional stress, can cause a brief, temporary rise. Smoking is associated with chronically higher WBC counts. Obesity may have a similar low-grade effect. Certain conditions — bone marrow disorders, autoimmune diseases, severe viral infections (such as HIV) — can reduce WBC production directly. Your GP will weigh up all of these factors, alongside the differential count and your symptoms, when interpreting the result.
When to act
If your WBC count is above the range on your report, consider whether you have had a recent infection, new medication, or any physiological stress around the time of the test. If so, a repeat count once you have recovered may simply confirm a return to normal. Most raised counts settle on their own. If your count is significantly elevated and you also feel persistently unwell, it is sensible to see your GP sooner rather than waiting for a routine appointment, so the cause can be checked. If your WBC count is below the range, particularly if neutrophils are low, speak with your GP about whether any precautions are needed while your immune system is running below its usual level. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
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