Hematocrit is the proportion of blood volume occupied by red cells, expressed as a percentage. It describes how thick or dilute the red cell fraction of the blood is, and it tracks closely with hemoglobin and the red cell count. Modern analysers usually calculate it from the cell count and mean cell volume rather than by spinning the sample.
No readings for this marker yet.
A lowered hematocrit most often accompanies anemia of any cause, or simple overhydration that dilutes the blood. A raised hematocrit most often reflects dehydration, and otherwise a sustained increase in red cell production from smoking, altitude, chronic lung disease, sleep apnoea or, less commonly, a bone marrow disorder. Because thicker blood flows less easily, persistently high values are followed up rather than left alone. What the shift means in a given person is for a doctor to judge against the rest of the picture.
Fluid balance is the dominant confounder, so the same person can test differently on a dehydrated morning and after a litre of water. Testosterone therapy raises red cell production and hematocrit is routinely monitored during it. The value is read together with hemoglobin and the red cell count, and with MCV and RDW when anemia is being characterised.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.