Different types of blood tests can be carried out to help identify people with a possible vitamin B12 or folate deficiency.
These tests 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
But some people can have problems with their normal levels of these vitamins, or may have low levels despite having no symptoms.
This is why it's 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 cannot.
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 blood test results suggest a vitamin B12 or folate deficiency, your GP may arrange further tests.
If the cause can be identified, it'll help to determine the most appropriate treatment.
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're unable to absorb vitamin B12 from the food you eat.
Tests for pernicious anaemia are not always conclusive, but can often give your GP a good idea of whether you have the condition.
Referral to a specialist
You may be referred to a specialist for further tests or treatment.
This may include:
- a specialist in treating blood conditions (a haematologist) – if you have vitamin B12 or folate deficiency anaemia and your GP is uncertain of the cause, you're pregnant or symptoms suggest your nervous system has been affected
- a specialist in conditions that affect the digestive system (a gastroenterologist) – if your GP suspects you do not have enough vitamin B12 or folate because your digestive system is not absorbing it properly
- a specialist in nutrition (a dietitian) – if your GP suspects you have a vitamin B12 or folate deficiency caused by a poor diet
A dietitian can devise a personalised eating plan for you to increase the amount of vitamin B12 or folate in your diet.
Find out more about B vitamins and folic acid for information about good sources of these vitamins.