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Hematocrit is the share of your blood that is made up of red blood cells. A level that is too low or too high can point to a blood condition, too little fluid in your body or other conditions that affect your blood.[1]
On this page you can read what haematocrit is, what the guidelines say about a value that is too low or too high, what affects your value and which other values are best read alongside it.
Also known as: HCT, packed cell volume, PCV, Crit, H and H. At the lab: KBB.
Hematocrit is a blood test that measures what share of your blood, as a percentage, is made up of red blood cells. Red blood cells carry oxygen from your lungs to the rest of your body. The other parts of your blood are white blood cells, which support your immune system, platelets, which help your blood clot to stop bleeding, and a fluid called plasma.[1]
Your result is a number: the percentage of your blood made up of red blood cells. If your result is 42, then 42% of your blood consists of red blood cells. The rest is white blood cells, platelets and plasma.[1]
The test is often part of a full blood count, which measures the number and type of cells in your blood. A doctor uses it to look at your general health. The test can also be included to follow how a value changes during care or with a condition that has been going on for longer.[1]
The share of red blood cells in your blood is linked to how oxygen is carried from your lungs to the rest of your body. A level that is too low or too high can point to a blood condition, too little fluid in your body or other conditions that affect your blood.[1]
Too few red blood cells is called anaemia. Symptoms that can come with it are shortness of breath, weakness or tiredness, headache, dizziness and a problem with the pace or rhythm of your heartbeat.[1]
Too many red blood cells can come with other symptoms: headache, light-headedness or dizziness, shortness of breath when you lie down, weakness or tiredness, itching after a bath or shower, a burning feeling or a red face, heavy sweating, especially while you sleep, blurred or double vision and blind spots, and unusual bleeding such as bleeding gums or a nosebleed.[1]
A result outside the normal range does not always mean there is a condition that needs care. Talk to your doctor to find out what your result says.[1]
The laboratory BioProfile works with, Labplusarts, uses a reference value for hematocrit (KBB) of 0.35 to 0.45 l/l. The lab calls a value between those limits normal.[2]
| Value | What it can mean | Who it is for |
|---|---|---|
| Lower than normal[1] | May point to blood loss from a wound or to blood loss that has been going on for some time | Everyone who takes the test |
| Lower than normal[1] | May point to too few red blood cells, anaemia | Everyone who takes the test |
| Lower than normal[1] | More fluid in the body than usual lowers the share of red blood cells | People who are pregnant |
| Higher than normal[1] | May point to too many red blood cells, for example with a lung disease or a heart condition | Everyone who takes the test |
| Higher than normal[1] | May point to too little blood plasma, usually from too little fluid | Everyone who takes the test |
| Higher than normal[1] | The body makes more red blood cells when there is less oxygen in the air | People who live at high altitude |
Source: MedlinePlus, U.S. National Library of Medicine, on what a hematocrit level that is too low or too high can mean. This source gives no numerical limits: what is normal differs by sex, by age, by whether you smoke and by the altitude at which you live.[1]
A level below normal can point to blood loss from an injury or blood loss that has been going on for longer. It can also point to too few red blood cells, anaemia, which comes in many forms with different causes. Sometimes the body makes too many white blood cells, for example with a condition of the bone marrow or of the blood. If you are pregnant, your body holds more fluid than usual and the share of red blood cells falls.[1]
A level above normal can point to too many red blood cells, for example with a lung disease, a heart condition or an uncommon condition in which you have too many red blood cells and your blood becomes too thick. It can also point to too little blood plasma. Too little fluid in your body is the most common cause behind a high level. If you live at high altitude, where there is less oxygen in the air, your body makes more red blood cells and a high level is to be expected.[1]
BioProfile is working on its own zones for each value, from risk to optimal. A doctor reviews those zones before they appear in your result.
Too little fluid lowers your blood plasma, and then the share of red blood cells gets bigger. If you are pregnant, it goes the other way: your body then holds more fluid than usual and your value may come out lower.[1]
Living at high altitude means less oxygen in the air. Your body responds by making more red blood cells, so that you get the oxygen you need. Because of this, your hematocrit can be high without anything being wrong.[1]
What counts as a normal haematocrit value differs by sex, by age, by whether you smoke and by the altitude you live at. Ask your doctor which value fits you.[1]
Blood loss from an injury can lower your level. The same goes for blood loss that has been going on for longer.[1]
Hematocrit is included in all five packages, from BioProfile 31 to BioProfile 150.[3]
The BioProfile editorial team wrote this page on 30 September 2026 from the sources below, which we read on 30 September 2026. Every number on this page appears in one of those sources, with the number of that source next to it. An expert still has to review this page; after that review, the name of that expert and the date of the review appear at the top. This page gives an explanation, not a diagnosis. Discuss an abnormal value with your GP.
