Hematocrit in women: what counts as normal?

Hematocrit expresses the share of your blood volume made up of red blood cells. A result of 0.41 l/l means 41 percent of your blood volume consists of red cells. Dutch laboratories report the value as a fraction rather than a percentage.

The test is now calculated rather than centrifuged. The cell counter multiplies the red cell count by the mean cell volume, the MCV. Those two values therefore always appear together on your report, and they belong together when reading it.

Reference values differ by sex and by age. Star-shl lists these bands, with the female band first:

Two things stand out. The band for women lies entirely below the one for men. Its lower limit is 0.35 l/l.

And children have their own band, which shifts with age. Comparing a child's result against an adult reference therefore leads to a wrong conclusion.

Reference values also differ per laboratory and per method. The range printed on your own report is therefore always the one that counts.

In women of reproductive age one cause dominates. Menstrual blood loss is by far the most common reason for a low hematocrit. Every cycle costs iron.

If the loss is heavy, the store empties slowly without you noticing.

The body refills that store from the gut in the meantime. When it cannot keep pace, red cell production comes under pressure. The order matters here.

Your ferritin empties first. Only afterwards do your haemoglobin and hematocrit fall.

That explains a common misunderstanding. A normal hematocrit does not exclude an iron deficiency. You can hold an empty store while your blood count still looks entirely fine.

Complaints such as fatigue, hair loss and restless legs belong precisely to that phase.

Pregnancy involves something quite different. Plasma volume rises faster than red cell mass. The steepest increase runs up to around week 30 to 34.

The cells spread across more fluid and the concentration falls. This is called physiological haemodilution. A lower hematocrit midway through pregnancy is therefore expected, and not in itself a sign of anaemia.

That is why maternity care works with cut-off values that move with gestational age. Assessing a value against the standard adult band would produce structural false alarms in that period.

Around menopause the picture shifts again. As menstruation ends, the largest route of iron loss disappears. A low hematocrit after menopause is therefore less readily explained, and warrants follow-up sooner than before.

Hematocrit almost always comes with a blood count. For women there are a few moments where the test adds information.

The first is persistent fatigue combined with heavy periods. Request not only the blood count then, but ferritin as well. Without that value you cannot see an empty store coming.

The second is trying to conceive, and pregnancy itself. Antenatal checks follow haemoglobin as standard, and hematocrit moves in the same direction. Always assess those results against the cut-off belonging to your gestational age.

The third is the period after birth. Blood loss around delivery can lower the value considerably for a time. Do not measure immediately afterwards, because the concentration only falls once the body has shifted fluid.

The cycle itself needs little worry. Hematocrit is not cycle-dependent the way hormones are. You can therefore draw blood on any cycle day.

It is sensible to wait briefly after a heavy bleeding day. That way you do not measure the trough.

Drink normally on the morning of the draw. Dehydration raises the concentration and can make a low hematocrit look artificially normal.