Leukocytes too high or too low

The test counts your white blood cells. On your result they appear as leukocytes, sometimes as leucocytes and sometimes simply as white blood cells; those are three names for the same thing. The number is given in x10^9/L, which amounts to billions of cells per litre of blood. White blood cells are made in your bone marrow and travel through your blood to wherever something needs clearing up.

At the laboratory the ordinary adult range runs from 4.3 to 10.0 x10^9/L. Sitting just above or just below that is not a problem in itself, because a reference range is the middle part of what healthy people have and draws no line between sick and healthy. Labs use slightly different limits from one another, for example 4.0 to 10.0 or 4.5 to 11.0. So compare your result with the reference column on your own report and not with a number you read somewhere else.

What many people do not know: this single number is a sum of five kinds of white blood cell that each do something different. Neutrophils go into action with bacterial infections and inflammation. Lymphocytes recognise viruses and make antibodies. Monocytes clear up after inflammation. Eosinophils respond to allergy and parasites, and basophils to allergic reactions. Few of one kind alongside many of another adds up to a normal number, so a normal total can hide a skewed distribution. If you want to know which type is out of range in your case, you need the leukocyte differential. You do not need to fast for this test.

The question almost everyone has with a raised number is simple: do I have an infection? The honest answer is that this number alone does not settle it, because it moves without infection too, and sometimes substantially.

These are the explanations to run through first. You were recently unwell; the number can still be raised. You had a stressful period or a bad night. You smoke; smokers sit higher on average, and after quitting the count comes down within a year. You exercised hard shortly beforehand. Or you had not drunk enough, so your blood was slightly concentrated.

That last one is easy to recognise. In dehydration all cell counts rise together. If your leukocytes, your haemoglobin, your haematocrit and your platelets all sit slightly higher, concentration is a more logical explanation than four conditions at once.

There is a daily rhythm too. In the morning your number sits lower than later in the day, so if you draw once at eight and once at four, that alone can explain a difference.

If you want to know whether inflammation is actually present, CRP often says more about that than this number alone. And if you want to know where a rise comes from, look at the differential. In an acute bacterial infection it is mainly the neutrophils that rise. Plenty of lymphocytes fits viral infections, among other causes.

So a single measurement is rarely the whole story. You mainly want to know whether an abnormality is still there on a repeat measurement.

You would usually have this measured as part of a general check, or with symptoms that could point to infection or inflammation: a fever that keeps returning, infections following one another, or fatigue you cannot explain.

Plan the draw so you get an honest picture. Give blood rested, and not shortly after exercising hard. Drink normally in the hours beforehand, otherwise you are mainly measuring your fluid deficit. Fasting is not needed.

As far as possible, draw at the same time of day as last time. Because of the daily rhythm, a morning result and an afternoon result are hard to compare.

Say whether you smoke, are pregnant or take medicines such as prednisone. All three shift the number predictably, and without that information a normal result can look abnormal.

Was your result mildly abnormal last time? Have it measured again: a repeat count is the first step to confirm or rule out an abnormality. Request the differential at the same time, because it tells you what the total cannot.