Leukocyte count in women

The count gives the number of white blood cells in a fixed volume of blood, expressed in x10^9/L. It is one number, but it consists of five cell types that each do something different. The leukocyte differential splits that total out. In women that breakdown is often the more interesting part of the result.

The most important life-stage influence is pregnancy. The white cell count rises physiologically during it, gradually and substantially. This is not inflammation and not infection, but a normal adaptation. During labour itself the value sits higher still. In the weeks afterwards it falls back.

That last point deserves emphasis, because it is widely assumed otherwise. Unlike the hormone values, where the cycle day determines the result entirely, the menstrual cycle barely shifts the leukocyte count. You therefore do not need to schedule this test for a specific cycle day.

For women this number matters above all for being read for the right reason. The two most common misunderstandings pull in opposite wrong directions.

The first is that the cycle drives this number. It very largely does not. Anyone used to scheduling hormone tests by cycle day understandably carries that habit over to the blood count. Here it adds nothing. Schedule the draw on practical grounds instead.

The second misunderstanding is more serious, because it causes needless worry. In pregnancy a value well above the ordinary reference range is normal. Set such a result against a standard range and it looks like an infection where there is none. Always assess a pregnancy result together with the gestational age, and include the differential.

There is a further reason not to read this number alone. In women with heavy menstrual blood loss, attention rightly turns to iron status. A normal leukocyte count says nothing about that iron status. For that you look at haemoglobin and above all at ferritin. Ferritin falls before the blood count changes. Fatigue with a normal leukocyte count is therefore not reassurance.

The general confounders apply here too. Smoking keeps the number chronically around 1 to 1.5 x10^9/L higher. Acute stress and heavy exertion raise it temporarily. Corticosteroids raise neutrophils while lowering lymphocytes. And in dehydration all cell counts rise together, so haemoconcentration can suggest a rise that is not real.

Unlike the hormone tests, you do not need to schedule this one for a particular cycle day. The leukocyte count barely moves with the cycle, so simply pick a moment that suits you.

What does count is the life stage. If you are pregnant, give the gestational age at the draw. Without that context a normal third-trimester value is quickly read as infection. Do you want to compare results from before, during and after pregnancy? Keep the measurement consistent: the same test, preferably at the same time of day.

Allow for the daily rhythm as well. Leukocytes sit lower in the morning than later in the day. Drawing at roughly the same time as last time makes two results more comparable. Fasting is not required.

Say whether you smoke or use corticosteroids. Do not draw within 24 hours of a hard training session or straight after a period of acute stress. Where possible run the test together with the differential. If fatigue or heavy menstrual bleeding is in play, include ferritin and haemoglobin as well.