How is anaemia diagnosed?


To diagnose anaemia, your doctor will ask you about your symptoms; review your medical history and risk factors you may have; and do a physical examination.  

During the physical examination your doctor may look for signs of bleeding; check to see whether the inner linings of your eyes and/or nails are pale; and listen to your heart.

There may also be clues as to the cause of the anaemia, e.g. yellow discolouration of the whites of the eyes (sclera) and skin, and enlargement of the liver and spleen in haemolytic anaemia. Complications of the underlying disease process may also be present, e.g. leg ulcers (as seen in thalassaemia).

Your doctor will order a blood test called a full blood count.

The following components of a full blood count may be abnormal:

  • Haemoglobin. This is likely to be reduced but in certain cases, such as in the early stages of iron deficiency, the haemoglobin may be normal. Iron studies will, however, show reduced ferritin levels (an indicator of iron stores) and a reduced mean corpuscular volume (MCV).
  • Haematocrit. This is the percentage of a sample of blood comprised of red cells and may be reduced.
  • Red cell count. This may also be reduced.
  • Mean corpuscular volume (MCV), a measurement of red blood cell volume. This may be reduced or increased.
  • In certain conditions, a reduced MCV may be one of the first indicators of anaemia before there’s a drop in haemoglobin. 

The blood cells themselves are examined under a microscope (this is called a “blood smear”). Specific abnormalities in the shape or appearance of the cells give clues to help your healthcare practitioner determine the underlying cause.

Iron studies
If iron deficiency is suspected as a cause of the anaemia, iron studies are ordered. Iron studies can also help to differentiate between anaemias that may share similar abnormalities on the full blood count (e.g. thalassaemia and iron-deficiency anaemia).

The components of iron studies are:

  • Serum iron. This measures circulating iron, most of which is carried in the blood bound to a protein called “transferrin”. Serum iron can fluctuate, depending on variations in dietary intake and the time of day the blood sample is taken. It’s therefore not a reliable indicator of the body’s iron status on its own. This blood test should ideally be taken after an overnight fast. If you have iron-deficiency anaemia, your serum iron levels will be low.
  • Transferrin or total iron-binding capacity (TIBC). This measures the level of transferrin, which transports circulating iron. It’s elevated in iron deficiency. 
  • Transferrin saturation. The ratio of serum iron to TIBC. This is low in iron deficiency.
  • Serum ferritin. Ferritin is the iron-storage protein in the blood that’s increased in proportion to the body’s iron stores. Very low ferritin levels (less than 15ng/ml) is diagnostic of iron deficiency. However, elevated ferritin doesn’t exclude iron deficiency, as other conditions such as inflammatory disorders can lead to a high ferritin level, even in the presence of low iron. 

Further testing to search for the cause of iron deficiency will be done if your doctor deems it necessary. These tests may include gastroscopy, colonoscopy and/or blood tests for H. Pylori infection and coeliac disease.  

If your doctor suspects that you have haemolytic anaemia, additional tests will be ordered. The abnormalities that may be seen include raised bilirubin and lactate dehydrogenase levels, and reduced haptoglobin levels. Antibody testing (the Coombs test) will be performed if the cause is thought to be autoimmune in nature.

Specific tests for genetic abnormalities will be done if an inherited cause is suspected.  

Based on the results of the above tests, your doctor may need to do even more tests, such as testing your bone marrow (a bone marrow biopsy). This can help to confirm the cause of your anaemia.

Reviewed by Cape Town-based general practitioner, Dr Dalia Hack. October 2018.

Read more:

- How is anaemia treated?

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