Hematocrit

What it is

Hematocrit is the share of your blood, by volume, that's made up of red blood cells rather than the liquid part (plasma) — imagine letting blood settle and measuring how much of the tube is cells. It tracks closely with hemoglobin and RBC count and is essentially never interpreted on its own. Because it's a ratio of cells to fluid, dehydration can raise it and extra fluid can lower it without anything changing about your red cells themselves, and it also varies by sex and altitude, so it's read as part of the overall red-cell pattern.

Typical range

Reference ranges vary between laboratories, and what is normal for you depends on your own history. Your own lab’s range is the one printed on your report.

Worth asking your clinician

• Do my hematocrit, hemoglobin, and RBC results line up with each other?
• Could how hydrated I was on the day of the draw explain this value?
• Is this consistent with my past results, or is it a change you'd want to keep an eye on?