Low white blood cell count
White blood cells are the cells that recognise microbes and destroy them. When they are scarce, infections take hold more easily, run a rougher course and…
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Medicines commonly prescribed for Low white blood cell count
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: INJECTABLE, 60 MU/ml of filgrastimActive substance: filgrastimManufacturer: Teva GmbhPrescription requiredDosage form: INJECTABLE, 48 Million IUActive substance: filgrastimManufacturer: Ratiopharm GmbhPrescription requiredActive substance: filgrastimManufacturer: Pfizer Europe Ma EeigPrescription required
White blood cells are the cells that recognise microbes and destroy them. When they are scarce, infections take hold more easily, run a rougher course and hide themselves better: the usual pus, redness and swelling may be missing simply because there is nobody left to produce them. A low figure on a blood test is not a disease in itself but a finding, and behind it there is a cause to look for. Those causes range from a harmless quirk of the body to a situation that needs treating the same day.
Which figure counts as low
A full blood count shows not just the total of white cells but the different types, and in practice one type dominates: the neutrophils, which meet bacteria and fungi first. A shortage of them is called neutropenia, and the risk of infection depends almost entirely on that rather than on the overall white cell count.
- Neutrophils below 1.5×10⁹/L — mild neutropenia. Most people with these numbers fall ill no more often than anyone else.
- Between 0.5 and 1.0×10⁹/L — moderate, with noticeably more infections.
- Below 0.5×10⁹/L — severe. Here any fever is treated as dangerous until proved otherwise. The extreme, when neutrophils all but disappear, is called agranulocytosis.
How quickly the figure moved matters too. A moderate dip that has held for years without infections is simply monitored. A sharp fall over a few weeks, particularly alongside anaemia or low platelets, is investigated urgently: that is how bone marrow disease announces itself.
When a low count is not an illness
Before starting any investigation, three common situations are worth ruling out.
An inherited trait. Many people of African and Middle Eastern descent permanently run fewer neutrophils than average, around 0.8–1.5×10⁹/L. This is not a disease: the cells simply spend more time in the tissues than in the bloodstream, and susceptibility to infection is not increased. Such people accumulate years of unnecessary tests and are sometimes denied treatment they need because of a "bad blood test". The clue is equally low figures in old results, together with a complete absence of infections.
After a viral infection. Flu, covid, glandular fever, parvovirus infection and ordinary colds push white cells down for one to three weeks. If the person feels well, repeating the test after a month is enough — the count almost always recovers on its own.
The test itself. The count varies through the day and shifts with stress, pregnancy and smoking, and cells clumping in the tube sometimes give a falsely low result. One isolated "bad" result with no symptoms is a reason to repeat the blood test, not to panic.
Why white cells fall
- Cancer treatment. Chemotherapy and radiotherapy suppress the bone marrow predictably; the lowest point usually falls in the second week after a cycle.
- Medicines. The commonest cause outside cancer care, and the easiest to put right. The usual culprits are antithyroid drugs (thiamazole, carbimazole, propylthiouracil), clozapine and some other antipsychotics, sulfasalazine, methotrexate, several antiepileptics, the painkiller metamizole and certain antibiotics.
- Infections. HIV, viral hepatitis, tuberculosis, brucellosis. In severe sepsis the white count does not rise but falls, and that is a bad sign rather than a reassuring one.
- Deficiencies. Lack of vitamin B12, folate or copper, and also serious undernutrition and alcohol dependence.
- Autoimmune disease: lupus, rheumatoid arthritis, Sjögren's syndrome. Sometimes a falling white count is the first sign, arriving before any joint or skin trouble.
- Bone marrow disease: leukaemias, myelodysplastic syndrome, aplastic anaemia, bone metastases. More than one blood line is usually affected at once.
- An enlarged spleen in liver disease, which traps and destroys blood cells.
Separate from all of these is congenital neutropenia, rare, which shows itself in early childhood with repeated severe infections and calls for lifelong haematology follow-up.
How it shows itself
Most often it does not: neutropenia turns up on a blood test ordered for something else. Where there are symptoms, they take the form of infections behaving out of character:
- colds, sore throats and chest infections following one another and lasting longer than expected;
- mouth and tongue ulcers, inflamed bleeding gums, a sore throat with nothing to see;
- boils, wounds that turn septic, inflammation around the nails;
- a lingering cough, repeated bouts of pneumonia;
- fever with no obvious source, chills, night sweats.
Tiredness on its own is rarely explained by the white cells: if it is there, anaemia or the underlying illness is what gets looked for.
Fever with neutropenia: do not wait
This is the one thing anyone with a low white count needs to know. A temperature of 38 °C or above during chemotherapy, or in the fortnight afterwards, is an emergency. With few neutrophils an infection unfolds over hours, and antibiotics need to start as soon as possible, usually within the hour. Do not wait until morning, until an appointment, or until you have taken the temperature again — and do not bring the fever down with paracetamol before being seen, because it masks the picture.
Contact your cancer unit immediately, or call an ambulance (in European countries, the single number 112), if with neutropenia there is:
- a temperature of 38 °C or above, or conversely below 36 °C with chills and shivering;
- fast breathing, breathlessness, confusion or unusual drowsiness;
- a fast weak pulse, cold clammy or mottled skin, a sharp drop in blood pressure;
- a rash that does not fade when pressed;
- little or no urine for many hours;
- severe abdominal pain, unstoppable vomiting, inability to keep fluids down.
These are the signs of sepsis. Tell whoever assesses you that your white cells are low and give the date of the last chemotherapy: how fast you are treated depends on it.
Without an ambulance, but the same day, see a doctor if you develop a sore throat, a temperature below 38 °C, a cough or any new infection, and also if you fall ill while taking thiamazole, clozapine or another of the drugs listed above.
What the doctor looks for and does
The starting point is a repeat full blood count with differential and a blood film under the microscope, which shows what the cells themselves look like. After that it depends: vitamin B12 and folate, ferritin, liver and kidney tests, HIV and hepatitis serology, autoimmune markers, an ultrasound of the spleen. The medication list is always gone through, because that is where the cause most often sits. If the other blood lines are down too, if the count is falling fast, or if immature forms appear on the film, a bone marrow examination is arranged.
What gets treated is the cause, not the number. The offending drug is stopped or swapped, and the count usually recovers over one to three weeks. Vitamin deficiencies are corrected and the underlying disease is treated. Infection means antibiotics; severe and prolonged neutropenia may call for medicines that speed up neutrophil production in the marrow, and marrow disease itself is managed by a haematologist. Persistent severe neutropenia is a reason to discuss preventive antimicrobials and vaccination: inactivated vaccines can and should be given, while live vaccines are not used while immunity is suppressed.
Keeping infections at bay
- Wash your hands more often than usual — before eating, on coming home, after the toilet and after handling animals.
- Look after teeth and gums: a soft brush, daily cleaning, and a dental check before chemotherapy starts rather than after.
- Cook meat, fish and eggs thoroughly, wash fruit and vegetables, watch use-by dates; during severe neutropenia it is worth setting aside raw meat, unpasteurised milk and the soft cheeses made from it.
- Clean and cover any wound straight away and try not to get cuts: an electric shaver rather than a blade, gloves for gardening and cleaning.
- Do not put off seeing a doctor because it is "only a cold", and do not start antibiotics on your own.
- During the respiratory infection season, keep away from unwell people and crowded indoor spaces where you can.
- While neutropenia is severe, hand over or postpone cleaning the cat litter tray, changing nappies and swimming in still water.
The point of all this is to get through the stretch when defences are down. There is no need to rehome pets or to isolate from the family: hygiene and common sense are enough.
Online consultation
A low white cell count lends itself well to a remote appointment, because here the results and the history matter more than the examination. The doctor will compare the new figure with your older ones, tell a lasting drop from a temporary post-viral dip, judge whether your particular number warrants concern, and say whether any investigation is needed at all. They will go through your medicines for anything capable of suppressing the marrow, say which tests come next and when to repeat the count, and clarify which vaccinations you can have now. Everyday matters fit into the same conversation: food, travel, work, exercise and mouth care during chemotherapy. And separately, they will name the signs that mean going straight to hospital rather than writing to the clinic.
This material is for information only and does not replace medical advice.
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