Empeiria

Hematocrit

Also known as Hct, PCV, packed cell volume

derived index · no single molecular formula

LOINC 4544-3 code verified whole_blood %

What this substance is

The share of blood volume taken up by red cells: a proportion, not a substance.
How it is calculated

Automated analysers: haematocrit (%) = RBC count (10^6/uL) x MCV (fL) / 10. Measured directly only as packed cell volume, by centrifuging a tube.

Derived from rbc_count, mcv.

Reference ranges

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This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

Hematocrit is usually part of a complete blood count (CBC). A health worker takes a small blood sample from a vein in your arm. Lab machines usually work out hematocrit from other red blood cell results in the same sample. You don't need to get ready in any special way.

Venous whole blood in a K2 EDTA tube, run as part of the CBC. On automated analysers such as the Coulter DxH 800, Hct is a calculated parameter (RBC x MCV), not separately measured; it should be approximately three times the hemoglobin. No special preparation; fasting only if other tests on the sample require it.

Before the test

  • No special preparation; fast only if other tests on the same sample require it.

Where: laboratory

Sources: Hematocrit Test, MedlinePlus (U.S. National Library of Medicine); Laboratory Procedure Manual: Complete Blood Count, NHANES 2015-2016, CDC National Center for Health Statistics cited · not yet checked by a person

In the lab

calculation

Calculated from RBC count and MCV

Hematocrit is the share of your blood taken up by red cells. Most machines work it out by multiplying how many red cells there are by how big they are on average.

On impedance analysers hematocrit is either measured from RBC pulse heights or, commonly, calculated as HCT (L/L) = RBC (10^12/L) × MCV (fL) / 1000. The reference method is the spun (centrifuged) hematocrit, against which analysers are calibrated.

  • Read by: None directly; derived from the measured RBC count and MCV

What can throw it off

  • Trapped plasma in spun (centrifuged) hematocrit
Why labs disagree: Hematocrit can be measured or calculated depending on the analyser, and a calculated value inherits any differences in the RBC count and MCV it is built from. Spun hematocrit traps plasma between the cells and reads higher than automated hematocrit, more so at high values, while analysers are calibrated against the spun method using samples with normal hematocrit. Different measurement procedures give different results, and hematocrit intervals differ between men and women, so labs are advised to set intervals on their own equipment.

Sources: Arbiol-Roca A et al. Reference intervals for a complete blood count on an automated haematology analyser Sysmex XN in healthy adults from the southern metropolitan area of Barcelona. EJIFCC 2018 (PMC5949618, open access); Girard S et al. Breaking Free From MCHC Interferences? French-Speaking Cellular Haematology Group (GFHC) Review of Causes, Rising Trends and Practical Solutions. Int J Lab Hematol 2025 (PMC12426809, open access) cited · not yet checked by a person

What it reports on

Associated symptoms

Conditions this marker features in

When high
  • high Too many red blood cells · defining
    Diagnostic threshold for polycythaemia vera (WHO 2016): above 49% in men and 48% in women. Dehydration is the most common cause of a high haematocrit, so a raised value is not always true polycythaemia.

Ordered as part of

cbc