Haematocrit is the proportion of a blood sample taken up by red blood cells, usually reported as a percentage. It is part of a blood count and is read with haemoglobin and the red cell indices. The range printed on your report decides how the value is read, not a figure from a website.
The number is easy to misread as a measure of blood volume or of how much blood a person has. It is neither. It is the red cell share of the sample in the tube, and that share depends on the plasma as much as on the cells.
What the test measures
Blood separates into red cells and plasma. Haematocrit compares the space the red cells take up with the space the whole sample takes up. When a laboratory spins a sample in a tube, the red cells pack at the bottom and the height of that layer against the total gives the packed cell volume, or PCV. That is the original form of the measurement.
Many modern analysers calculate haematocrit from the red cell count and the mean cell volume instead of spinning the sample. The printed haematocrit and a spun packed cell volume can therefore differ a little, and the report may not say which method was used. Neither version measures total blood volume. A person can have a haematocrit outside the printed range while the total amount of red cells in the body is unchanged, because plasma volume moved.
Haematocrit and haemoglobin usually move together. They are linked through the concentration of haemoglobin inside the cells, which is what MCHC describes. When the two lines disagree, the report is telling you something about the cells or the sample, and it is worth reading the indices before drawing a conclusion.
Why it may be ordered
- As part of a complete blood count, where it is reported beside haemoglobin and the red cell indices.
- When anaemia or a change in blood volume is being assessed.
- In pregnancy, where plasma volume expands and the result is read against pregnancy-specific ranges.
- Before surgery or a procedure, as part of a general assessment.
- When dehydration or fluid overload is a question.
- To follow a known blood condition over time.
It is rarely ordered on its own. A haematocrit without haemoglobin, the red cell indices, and the clinical question would be a single proportion with no context.
The unit on your report
| What you may see | What it means |
|---|---|
| Haematocrit, hematocrit, Hct | The test name. Laboratories use different spellings and abbreviations for the same measurement. |
| PCV, packed cell volume | The same proportion, under the name used when the sample is spun in a tube. |
| % | The red cell share of the sample volume, expressed as a percentage. |
| L/L | The same proportion written as a fraction of a litre per litre. The decimal form and the percentage form describe one value. |
| Hct (calc.) | A calculated value, derived from the red cell count and MCV rather than measured by spinning. |
Why this page does not print a range
A reference range belongs to the laboratory, the method, and the group of people it was built from. Ranges can differ with age and sex, pregnancy has its own ranges, and the clinical context changes how a result is read. Altitude and smoking can shift what is usual for a person, and the analyser and calibration can shift the value on the same sample.
The range printed on the report that produced your value is the one that applies. Doctano keeps that printed range with the result and does not replace it with a general range. If a report prints the proportion as a fraction rather than a percentage, read the range that matches that notation.
What a high value can mean
A higher proportion of red cells can reflect a smaller plasma volume rather than more red cells. Possible contributors include dehydration from vomiting, diarrhoea, fever, or fluid loss, and medicines that increase urine output. It can also reflect a genuine increase in red cell production, which can be associated with chronic low oxygen from lung disease, time at high altitude, smoking, and some kidney or bone marrow conditions.
The number does not separate these possibilities. A high haematocrit on one sample may be a hydration effect, and a clinician may repeat the test before treating it as a change in the person. A high value does not confirm or rule out any condition.
What a low value can mean
A lower proportion can reflect fewer red cells, more plasma, or both. Possible contributors include anaemia from reduced production, increased loss, or increased destruction, and dilution from pregnancy, intravenous fluids, or fluid retention. Blood loss lowers the proportion, though the change may lag behind the loss until the plasma volume is restored.
A low haematocrit is not a diagnosis and does not identify a cause. It is read with haemoglobin, MCV, MCH, RDW, and the red cell count, and a clinician may look at a blood film when the lines do not fit together.
What can move the value
- Plasma volume. Fluid loss concentrates the sample; fluid intake or intravenous fluids dilute it.
- Posture and tourniquet time. A long tourniquet concentrates the sample in the tube.
- Sampling from an infusion arm. Fluid running into the same arm can dilute the sample.
- Pregnancy. Plasma volume expands, and the proportion usually falls.
- Altitude. Living or staying high above sea level can raise it over time.
- Method. A calculated haematocrit and a spun packed cell volume can differ slightly.
- Sample storage. Red cells can change volume after collection, and delayed analysis can shift the result.
- Transfusion or blood loss. Either changes the cells available to be counted.
What to compare it with
Read haematocrit with haemoglobin, MCV, MCH, and the red cell count on the same report. If haemoglobin and haematocrit disagree, MCHC usually shows it, and the reason can lie in the sample, the cells, or the calculation. RDW adds whether the cell population is uniform or mixed.
The most useful comparison is the previous haematocrit from the same laboratory, in the same notation. A change between two laboratories can reflect the method as much as the person.
How to see the trend
Doctano reads the haematocrit value, its unit, and the reference range printed on the report. It keeps that range with the result, normalizes the marker name across labs, and places the value on the profile's timeline. Each point still opens the report it came from, so the original page can be checked.
When one report prints a percentage and another prints a fraction, Doctano normalizes the notation for the timeline. Verify the value and the unit against the original report before treating a change as real, especially when the two results came from different laboratories.
What this page is not
This page explains the test in general. It does not interpret your result, diagnose a condition, or recommend treatment. It is not medical advice. Verify the value and the unit against the original report, and discuss the result with a qualified professional.