Haematocrit
Haematocrit is how much of your blood is made up of red blood cells — the cells that carry oxygen. A result inside the range on your report usually means your red cell numbers are in the expected range. A low result can point to anaemia (too few red cells), while a high one is often just dehydration. It moves together with your haemoglobin and red cell count, so it is always read as part of the set.
Standard CareWhat is haematocrit?
Haematocrit — sometimes called packed cell volume (PCV) — tells you what fraction of your blood is made up of red blood cells. If your haematocrit is 0.45 L/L, for example, that means 45% of your blood volume consists of red cells; the remainder is plasma and other blood components. Red blood cells carry oxygen from your lungs to your body's tissues using a protein called haemoglobin. Because haematocrit reflects how many red cells are present, it moves closely in step with haemoglobin (the total amount of oxygen-carrying protein) and the red blood cell count (the number of cells). All three are reported together on a full blood count (FBC) — a routine panel run from a single tube of blood. The haematocrit is useful precisely because it is so closely linked to haemoglobin: together they give a fuller picture of your blood's oxygen-carrying capacity than either alone.
Why is it tested?
Haematocrit is ordered as part of a full blood count when your GP wants to assess your blood's oxygen-carrying capacity. Common reasons include investigating tiredness, breathlessness, dizziness, or pale skin — symptoms that can suggest anaemia. It is also used to monitor known conditions such as iron deficiency, chronic kidney disease, and inflammatory bowel disease, and to check in before or after surgery. The haematocrit is read alongside haemoglobin, the red blood cell count, and the red cell indices — MCV (the average size of your red cells), MCH and MCHC (how much haemoglobin those cells carry). If the result is low, your GP may order follow-up tests such as iron studies, ferritin, vitamin B12 and folate to find the underlying cause.
Reference range (Australia)
Full blood count reference intervals are set by each laboratory and depend on the analyser platform used. Red cell measures — including haematocrit — are sex-specific: the range for men is generally higher than for women. The interval printed on your own pathology report is the one that applies to you.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A haematocrit below the reference range means a smaller proportion of your blood than expected is made up of red cells. This is consistent with anaemia — a reduction in the blood's ability to carry oxygen. Anaemia is one of the most common findings on a blood test. It is a finding, not a diagnosis: the cause still needs to be found. The most common cause is iron deficiency. Other causes include a shortage of vitamin B12 or folate (both needed to make red cells), chronic disease or inflammation, and blood loss. Less often, a problem with the bone marrow is involved. A low haematocrit is worth raising with your GP. They will read it alongside haemoglobin and the red cell indices on the same report, and consider your symptoms and history, before deciding on next steps.
Your haematocrit falls within the range printed on your report, suggesting the proportion of red cells in your blood is adequate. If you have symptoms such as persistent tiredness or breathlessness despite a normal result, it is still worth raising with your GP — they may wish to look at trends or check related markers such as haemoglobin and ferritin.
A haematocrit above the reference range on your report means a larger proportion of your blood than usual is made up of red cells. The most common reason is dehydration: when plasma volume falls, red cells become more concentrated and the haematocrit rises. This typically corrects once hydration is restored. Other causes include smoking, living at high altitude, and a condition called polycythaemia (also written erythrocytosis), in which the body produces more red cells than usual — either as a normal physiological adaptation or, less commonly, as a bone marrow condition. A mildly raised result that normalises on a repeat test is usually not a concern. Mention it to your GP so they can put it in context with your haemoglobin and red blood cell count.
What can affect your result
Haematocrit reflects the balance between red cell production and red cell loss or destruction, and is also sensitive to changes in plasma volume. Hydration is the most immediate influence: dehydration concentrates the blood, raising haematocrit; overhydration dilutes it, lowering the result. This means a single result can look different depending on when and how hydrated you were at the time of the test. Iron, vitamin B12, and folate are all essential for making red blood cells. A shortfall in any of these reduces red cell production and lowers haematocrit alongside haemoglobin. Chronic disease and inflammation — including kidney disease, rheumatoid arthritis, and cancer — can suppress red cell production and lower haematocrit even when nutrients appear adequate. Altitude and smoking both stimulate the body to produce more red cells as an adaptation to lower oxygen availability, which can raise haematocrit. Blood loss — from heavy periods, gastrointestinal bleeding, or surgery — acutely reduces red cell numbers and lowers haematocrit.
When to act
If your haematocrit is outside the reference range on your report, share the result with your GP. They will read it alongside haemoglobin and the red cell count — which usually move together — as well as your symptoms and history, before deciding whether any follow-up is needed. A mildly low result in someone who feels well is often transient and may settle on its own, especially if hydration or diet is a likely factor. A pattern of falling results over time, or a result that is low alongside a low haemoglobin and symptoms, warrants further investigation. If your result is high, your GP can assess whether dehydration or another cause is most likely. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
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