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Red blood cells are the red cells in your blood. They are made in your bone marrow and contain hemoglobin, an iron-rich protein that carries oxygen from your lungs to every cell in your body. A result that is higher or lower than normal is often the first sign of illness: a low value can point to anaemia, a high value to dehydration.[1]
On this page, you can read what erythrocytes are, 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: red blood cells, erythrocyte count, RBC. At the lab: KBB.
A red blood cell count measures the number of red blood cells in your blood. Red blood cells are made in your bone marrow, the spongy tissue inside your large bones.[1]
Those cells contain hemoglobin, an iron-rich protein that carries oxygen from your lungs to every cell in your body. Your cells need oxygen to grow, divide and make the energy that keeps you functioning.[1]
The test is also called a red blood cell count or RBC. It is almost always part of the full blood count, a group of tests that measures the number and type of cells in your blood. The result helps detect problems with your red blood cells, such as anaemia, where your body does not make enough healthy red blood cells.[1]
A red blood cell count that is higher or lower than normal is often the first sign of illness. That is why this value appears on a result so often.[1]
You often get the test as part of a full blood count during a routine check-up. A doctor may also ask for it if you are receiving care that can affect your blood cells, to follow how things are going with a long-term kidney condition, or if you have symptoms that fit a low or high value.[1]
With a low value, you may be short of breath, feel weak or tired, have headaches or dizziness, notice a problem with the pace or rhythm of your heartbeat, or have pale skin. With a high value, you may have headaches, dizziness or problems with your vision.[1]
If your result is low or high, more tests may follow to complete the picture: a reticulocyte count, which counts the still young red blood cells and shows whether your bone marrow is making enough of them, iron tests, or a test for vitamin B.[1]
Labplusarts, the laboratory BioProfile works with, uses a reference value of 4.5 to 5.5 10^12/l for red blood cells (KBB). The lab calls a value between those limits normal.[2]
| Result | What it can point to | Who it is for |
|---|---|---|
| Lower than normal[1] | Anaemia, too few calories, vitamins or minerals, a condition of the blood or bone marrow, a kidney condition, blood loss from a wound, a condition caused by alcohol use, or being pregnant | People whose count comes out lower than normal |
| Normal[1] | The count is neither too low nor too high | People whose count is normal |
| Higher than normal[1] | Dehydration, a heart condition, a lung disease, scarring in the lungs often from smoking, a kidney condition, a condition in which you keep stopping breathing in your sleep, or a disease in which your bone marrow makes too many red blood cells | People whose count comes out higher than normal |
MedlinePlus, U.S. National Library of Medicine, Red Blood Cell (RBC) Count: this source's own grouping into a low, a normal and a high count, for people who have this blood test.[1]
A low count can point to anaemia, where your body does not make enough healthy red blood cells. Too few calories, vitamins or minerals, a condition of the blood or bone marrow, a kidney condition, blood loss from a wound, a condition caused by alcohol use and being pregnant can also lower the count. Symptoms that can come with it are shortness of breath, weakness or tiredness, headaches, dizziness, a problem with the pace or rhythm of your heartbeat and pale skin.[1]
A high count can point to dehydration, a heart condition, a lung disease, scarring in the lungs that is often caused by smoking, a kidney condition, a condition where you repeatedly stop breathing in your sleep, or a disease where your bone marrow makes too many red blood cells. Symptoms that can come with it are headaches, dizziness and problems with your vision. Talk to your doctor about your result: they will also look at your symptoms, your medical history and your other blood values.[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.
Dehydration is one of the things that can cause a high count. Your blood then contains less fluid, and that affects the result.[1]
Living at high altitude can lead to a high number of red blood cells. If you live at high altitude, tell your doctor when your result is being read.[1]
Scarring in the lungs is often caused by smoking cigarettes, and this kind of scarring can lead to a high number of red blood cells.[1]
Misusing certain substances to boost sports performance can push the count up. A condition caused by alcohol use can instead bring the count down, as can being pregnant.[1]
Red blood cells are 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.
