• The Red Blood Cell (RBC) count measures the number of red cells circulating in your blood.
• The test is included as part of a full blood count (FBC) a routinely ordered general health test which measures other types of blood cells at the same time.
• RBCs carry oxygen throughout the body. Having too few or too many RBCs can be a sign of many different health conditions.
• If you have too few RBCs, you are said to be anaemic. Too many RBCs and you have polycythaemia.
• The results of a RBC count need to be considered along with the results of other tests in the FBC including haemoglobin and haematocrit.

Your blood is made up of red blood cells (RBCs), white blood cells (WBCs) and platelets. These float in fluid called plasma.

RBCs are the most common type of blood cell – they make up almost half of your blood - and they play an essential role in carrying oxygen to every cell in your body. All cells in every part of your body need oxygen to make energy so that they can function properly.

In order to produce energy, oxygen combines with glucose, which you get from the food you eat. This process releases water and bicarbonate.

As a waste product, bicarbonate passes from the cells back into the blood where it is carried to your lungs to be breathed out as carbon dioxide.

RBCs can carry oxygen because they contain haemoglobin, the red protein that gives the blood its colour. Both oxygen and bicarbonate bind to the haemoglobin in RBCs so they can be transported.

How are red blood cells made?

Blood cells are made in your bone marrow, the soft fibrous tissue inside many of your bones. In order to stay healthy, your body must constantly make new blood cells to replace old ones. In general, RBCs have a lifespan of about 120 days.

New RBCs are produced as stem cells in the bone marrow. They develop through several stages into mature cells. RBCs stay in your bone marrow until they are needed and then are released into your blood. Mature RBCs are known as erythrocytes. They are round with a flattish, indented centre, like a doughnut without a hole.

The purpose of the RBC count is to find out if the number of RBCs you have is normal or abnormal. An RBC count is always included as part of a Full Blood Count (FBC) - a very common tests that assesses the health status of all your blood.

• It measures the number and the size of RBCs, WBCs, and platelets in your blood.
• It helps screen for, diagnose, and monitor conditions that affect your blood or bone marrow.

Too few RBCs – anaemia

If the number of RBCs in your blood sample is10 per cent under what is considered normal, you are said to be anaemic.

Too many RBCs – polycythaemia (erythrocytosis)
If you have too many RBCs you are said to have polycythaemia. This makes your blood thicker than it should be, and without treatment it could increase your risk of blood clots.

There are two types of polycythaemia. Primary polycythaemia is due to a bone marrow problem (myeloproliferative neoplasm) as in polycythaemia vera (PV). PV is a condition in which the bone marrow produces too many RBCs, along with high numbers of WBCs and platelets. It is caused by a variant or mutation in particular genes, especially the JAK2 gene which is responsible for making a protein that is needed to produce blood cells.

Secondary polycythaemia is more common and occurs when a health condition is preventing oxygen from getting to your tissues. This may be due to problems with lung function, heart function or rarely, due to problems with the kidneys or adrenal glands (small glands on your kidneys). Your body makes up for lower oxygen levels by making more blood cells that can carry more oxygen.

Tests that are used together with the RBC count

The results of other tests included in the FBC will be used to assess your RBCs.

• Haemoglobin This is the iron-containing, oxygen-carrying red protein in RBCs. Measuring it can show if you don’t have enough iron or enough vitamins such as vitamin B12 and folate that are needed to make haemoglobin. Low haemoglobin levels cause anaemia.
  Haemoglobin results are used in making calculations to gain more details about your red blood cells.
  • Mean cell haemoglobin (MCH) This is calculated by dividing the total amount of haemoglobin by the total number of RBC in a blood sample. This gives the average amount of haemoglobin inside each RBC. The MCH is increased in macrocytic anaemias (larger red blood cells) and decreased in microcytic anaemias (small red blood cells).
  • Mean cell haemoglobin concentration (MCHC) is calculated by dividing the total amount of haemoglobin by the amount of space RBCs are taking up in your blood sample (the volume of RBCs). It shows the concentration of haemoglobin inside a red blood cell and takes into account the cell's volume. This can give more detail about your condition.
• Haematocrit This measures the percentage of RBCs in your blood. High haematocrit suggests polycythaemia, low haematocrit points to anaemia.
• Mean Cell Volume (MCV) MCV measures the average size of your RBCs. It is high when your cells are larger than normal (macrocytic) such as in vitamin B12 deficiency, folate deficiency, liver disease or hypothyroidism (when your thyroid gland is not making enough hormones). When the MCV is lower, your RBCs are smaller than normal (microcytic) as in iron deficiency anaemia and the inherited condition, thalassaemia.
• Reticulocyte count (in some circumstances) RBCs that are not fully developed are known as reticulocytes. Most red blood cells are fully mature before they are released but a tiny amount are released into the blood as reticulocytes. Reticulocytes can be distinguished from mature red blood cells because they still contain remnant genetic material (RNA) inside the cells which is not found in mature red blood cells. Circulating reticulocytes generally lose their RNA within one to two days, thus becoming mature red blood cells. A reticulocyte count can help show if your bone marrow is making enough RBCs and give information that will help identify the cause of low or high RBCs.

Possible further tests for anaemia

• Iron studies (Ferritin, transferrin and transferrin saturation/TIBC). This measure iron levels in your blood. Iron is essential for making RBCs.
• Vitamin B6, vitamin B12 and folate tests Having adequate levels of these is important for making haemoglobin.

Sample

Blood.

Any preparation?

None.

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Reference intervals - comparing your results to the healthy population

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• They are used to provide a benchmark for interpreting a patient's test results.
• When compared against them, your results may be flagged high or low if they sit outside this range.
• Some reference intervals are harmonised or standardised, which means all labs in Australia use them.
• Others are not because for these tests, labs are using different instruments and chemical processes to analyse samples.
• Always compare your lab results to the reference interval provided on the same report.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation.

Reference intervals for the RBC count vary between labs so you will need to go through your results with your doctor. Your doctor is the best person to interpret your results.

• An RBC count that is higher or lower than normal is often the first sign of an illness.
• Normal decreases in RBCs are seen during pregnancy
• Living at high altitudes causes an increase in RBC counts; this is your body's response to the decreased oxygen available at these heights.
• Drugs that may increase RBC levels include gentamicin and methyldopa.

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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