Haematology
Haematocrit
Haematocrit, also written as Hct or packed cell volume, is the proportion of whole blood occupied by red cells, expressed as a percentage or fraction. At the point of care it is most often derived from the electrical conductivity of a whole-blood sample on a cartridge-based blood gas and chemistry analyser, or calculated from an optically measured total haemoglobin.
Why it is measured
Haematocrit gives a rapid bedside read on red cell mass and is used to screen for anaemia or polycythaemia and to gauge haemodilution, haemoconcentration and fluid status during acute and perioperative care. It is also paired with haemoglobin to support transfusion and resuscitation decisions.
| Typical range | Indicative adult range roughly 0.40 to 0.54 (40 to 54 percent) for men and 0.36 to 0.46 (36 to 46 percent) for women. Ranges are sex specific and vary by method, device and population, so always apply the local laboratory or manufacturer range. |
|---|---|
| Sample | Whole blood, typically a small heparinised arterial, venous or capillary sample drawn directly into the analyser cartridge or syringe. Conductivity-based results can be affected by abnormal plasma protein or electrolyte concentrations. |
| Turnaround | Typically under 1 to 2 minutes from sample application, reported alongside the blood gas and electrolyte panel. |
Point of care devices that report it
- Abbott i-STAT
- Siemens Healthineers epoc Blood Analysis System
- Werfen GEM Premier 5000
- Radiometer ABL90 FLEX
- Nova Biomedical Stat Profile Prime Plus
Questions, answered
Why does the point-of-care haematocrit sometimes differ from the laboratory result?
Many point-of-care analysers estimate haematocrit from whole-blood conductivity, whereas laboratory haematology analysers calculate it from measured red cell counts and volumes. Differences in method mean small discrepancies are expected, and abnormal plasma proteins or electrolytes can shift the conductivity-based value. Method and device should always be noted when comparing results. This is general educational information only.
What is the relationship between haematocrit and haemoglobin?
Haematocrit and haemoglobin both reflect red cell mass and usually move together, with haematocrit often roughly three times the haemoglobin in g/dL as a rough rule of thumb. Some point-of-care devices report a haemoglobin value calculated from the measured haematocrit, while others measure haemoglobin optically and derive the haematocrit. This is general educational information, not a basis for interpreting an individual result.
Does the sample type or anticoagulant matter for point-of-care haematocrit?
Yes. Use the sample type and anticoagulant specified by the manufacturer, commonly balanced heparin, and avoid excess anticoagulant, air bubbles, clots or delayed analysis, as these can bias the result. Follow the device instructions for use and local standard operating procedures.