Anaemia, vitamin B12 or folate deficiency - Diagnosing vitamin B12 or folate deficiency anaemia

A diagnosis of vitamin B12 or folate deficiency anaemia can often be made by your GP based on your symptoms and the results of blood tests.

Blood tests

Different types of blood tests can be carried out to check:

  • whether you have a lower level of haemoglobin (a substance that transports oxygen) than normal
  • whether your red blood cells are larger than normal
  • the level of vitamin B12 in your blood
  • the level of folate in your blood

These tests can often help identify people with a possible vitamin B12 or folate deficiency, but they are not necessarily conclusive, because some people can have problems with normal levels of these vitamins, and others can have low levels despite having no symptoms.

This means it is very difficult to devise definitive criteria for the diagnosis of vitamin B12 or folate deficiency, and this is why it is important for your symptoms to be taken into account when a diagnosis is made.

A particular drawback of testing vitamin B12 levels is that the current widely-used blood test only measures the total amount of vitamin B12 in your blood.

This means it measures forms of vitamin B12 that are "active" and can be used by your body, as well as the "inactive" forms, which can't. If a significant amount of the vitamin B12 in your blood is "inactive", a blood test may show that you have normal B12 levels, even though your body cannot use much of it. 

There are some types of blood test that may help determine if the vitamin B12 in your blood can be used by your body, but these are not yet widely available.

Identifying the cause

If your symptoms and test results indicate you are likely to be deficient in either vitamin B12 or folate, your GP may arrange further tests to help identify the cause. This will help determine the most appropriate treatment for you.

For example, you may have additional blood tests to check for a condition called pernicious anaemia. This is an autoimmune condition (where your immune system produces antibodies to attack healthy cells), which means you are unable to absorb vitamin B12 from the food you eat.

Like the blood tests used in diagnosing vitamin B12 or folate deficiencies, tests for pernicious anaemia are not always conclusive, but they can often give your GP a good idea of whether you have the condition.

Referral to a specialist

In some circumstances, you may be referred to one of the following specialists.

Haematologist

A haematologist is a doctor who specialises in treating blood conditions. You will probably be referred to a haematologist if you have vitamin B12 or folate deficiency anaemia and:

  • your GP is uncertain what is causing the condition
  • you are pregnant
  • your symptoms suggest your nervous system (the brain, nerves and spinal cord) has been affected  this can cause problems such as changes in your vision, and numbness and tingling in your hands and feet

Gastroenterologist

A gastroenterologist is a doctor who specialises in conditions that affect the digestive system. You may be referred to a gastroenterologist if your GP suspects you do not have enough vitamin B12 or folate because your digestive system is not absorbing it properly.

For example, your GP may refer you to a gastroenterologist if they suspect you may have coeliac disease or Crohn's disease.

Dietitian

A dietitian is a healthcare professional who specialises in nutrition. They can give you advice about your diet.

You may be referred to a dietitian if your GP suspects you have a vitamin B12 or folate deficiency caused by a poor diet. The dietitian can devise a personalised eating plan for you to increase the amount of vitamin B12 or folate in your diet.

Read our page on B vitamins and folic acid for information about good sources of these vitamins.

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