• Haemoglobin is the red protein in red blood cells that gives them their colour.
• Red blood cells carry oxygen from your lungs to your body’s tissues and return bicarbonate from the tissues back to the lungs to be breathed out as carbon dioxide.
• Red blood cells can do this because they contain haemoglobin. 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 red blood cells, your body will not be able to get enough oxygen, causing fatigue and weakness.

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.

Haemoglobin is the red protein in RBCs that gives them their colour. Haemoglobin is made in the bone marrow, the spongy tissues inside many of your bones. To make haemoglobin, your body needs iron, and to make RBCs, your body needs vitamin B12 and folate.

Iron

Iron is crucial for making haemoglobin because it contains haem. Haem is the part of iron that binds to oxygen. Our bodies cannot make iron. It must be absorbed from our diet or from supplements. The amount of iron we absorb is decided by our body's needs. When we don’t have enough iron, our bone marrow cannot make haemoglobin because we do not have enough haem, which can lead to iron deficiency anaemia.

Vitamin B12 and folate

Vitamin B12 and folate are needed to make RBCs. (They are also needed to make and repair DNA and nerve cells.) If we don’t have enough vitamin B12 or folate, it can lead to a type of anaemia called megaloblastic anaemia, in which RBCs aren’t formed properly in our bone marrow, and they don't function properly, reducing their oxygen-carrying capacity.

Measuring the amount of haemoglobin in your blood can help find out if you have enough RBCs to transport oxygen throughout your body. It helps screen for, diagnose, and monitor conditions that affect your blood or bone marrow. For more on this see red blood cell count.

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 haemoglobin

A measurement of haemoglobin is included in the full blood count (FBC), a routinely used test that assesses all the parts of your blood. It measures the number and the size of RBCs, white blood cells (WBCs), and platelets in your blood.

A haemoglobin test may also be ordered on its own if you are suspected of having a condition affecting your RBCs as well as to monitor any treatment you are having for a blood or bone disorder.

The test is also used before a surgical procedure to help make decisions about blood transfusion. It is also used to monitor a person’s condition if they have ongoing bleeding problems.

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

• Red Blood Cell (RBC) count measures the number of red cells in your blood.
• Haematocrit This measures the percentage of RBCs in your blood. High haematocrit suggests polycythaemia (too many RBCs), low haematocrit points to anaemia (too few RBCs).
• 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.

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.

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 red blood cells.
• Vitamin B6, vitamin B12 and folate tests Having adequate levels of these is important for making haemoglobin.

For more information see full blood count (FBC), and red blood cell (RBC) count.

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 haemoglobin 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.

• Haemoglobin decreases slightly during normal pregnancy.
• Haemoglobin levels show mild daily changes, tending to be highest in the morning and lowest in the evening.
• Heavy smokers have higher haemoglobin levels than non-smokers.
• Living in high altitudes increases haemoglobin levels. This is your body's response to the decreased oxygen available at these heights.
• Haemoglobin levels are slightly lower in older men and women and in children.

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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