Summary

• Red cell indices are a group of blood tests that measure the size of red blood cells (RBCs).
• They also measure or calculate how much haemoglobin is being carried by RBCs. Haemoglobin is the red protein in red blood cells that transports oxygen.
• As components of the Full Blood Count (FBC), they are used to investigate anaemia and vitamin deficiencies, bone marrow disorders and liver disease.

What are red blood cells?

Red Blood Cells (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. All cells in every part of your body need oxygen to make energy so that they can function properly.

RBCs can carry oxygen because they contain haemoglobin. Haemoglobin is the red protein in RBCs that gives them their colour. Oxygen sticks to the haemoglobin in red blood cells so it can be transported.
If your haemoglobin levels are low, or if you have too few RBCs, your body will not be able to get enough oxygen, causing fatigue and weakness.

To stay healthy, your body must make new RBCs to replace those that age and degrade or are lost through bleeding.

Blood cells are continually being renewed. Old cells are removed and new cells are produced in the bone marrow, the soft fibrous tissue inside many bones, and then released into your blood stream. RBCs develop from stem cells through several stages into mature cells to be released into the blood. RBCs typically survive for about 120 days in circulation.

Some health disorders can cause red blood cells to become larger or smaller. If it is associated with anaemia, it means that RBCs are unable to carry enough oxygen.

RBCs can become smaller when there is a problem making enough haemoglobin. If haemoglobin production is low, the bone marrow produces many small cells. RBCs become larger when they cannot divide properly during development. When the cell cannot divide, it stays big.

Microcytic (RBCs are smaller than normal)

Can be due to:

• Iron deficiency anaemia
• Thalassaemia
• Chronic disease

Macrocytic (RBCs are larger than normal)

Can be due to:

• Vitamin B12 deficiency
• Folate deficiency
• Bone marrow disorders
• Liver disease
• Alcohol use
• Medications such as chemotherapy, antiretrovirals

Normally, RBCs are uniform in size and shape, but some health disorders cause them to vary in size.

Anisocytosis (RBCs are of different sizes)

Can be due to:

• Iron deficiency anaemia
• Vitamin B12 or folate deficiency
• Haemolytic anaemia
• Recent blood loss

Poikilocytosis (RBCs take on different shapes)

Can be due to:

• Iron deficiency anaemia
• Thalassemia
• Megaloblastic anaemia (B12 or folate deficiency)
• Hereditary RBC disorders
• Liver disease
• Kidney disease
• Bone marrow disorders
• Bone marrow infiltration (cancers, myelofibrosis)
• Sickle cell disease
• Severe burns

What are red cell indices?

Red cell indices are a group of blood tests that measure the size of RBCs and calculate how much haemoglobin is being carried. As components of the Full Blood Count (FBC), they are used to investigate anaemia and vitamin deficiencies, bone marrow disorders and liver disease. There are four tests.

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 low, your RBCs are smaller than normal (microcytic) as in iron deficiency anaemia and the inherited condition thalassaemia.

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)

This 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.

Red cell distribution width (RDW)

RDW is a calculation of how much variation there is in the size of your RBCs. If all red cells are about the same size, you will have a normal RDW. If there is a wide mix of small and large red cells you will have a high RDW.

Your doctors may also order a reticulocyte count. RBCs that are not yet fully developed are known as reticulocytes. Most red blood cells are fully mature before they are released from the bone marrow into the blood, but a tiny number of RBCs are released as reticulocytes. A reticulocyte count can help show if your bone marrow is making enough RBCs and gives information that will help identify causes of anaemia.

Having the test

Sample
Blood

Any preparation?
None

Your results

Reading your test report

Your results will be presented along with any other tests your doctor ordered on the same form. You will see separate columns or lines for each of these tests. Your results may be flagged as high (H) or low (L).

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.

Questions to ask your doctor

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?

More information

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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