Vitamin B12 and folate are primarily requested to help diagnose the cause of macrocytic anaemia. They can be requested as follow-up tests when large red cells and a decreased haemoglobin concentration are found during a FBC test. Folate and vitamin B12 may be used to help evaluate the nutritional status of a patient with signs of significant malnutrition or malabsorption. This may include those with alcoholism and those with disorders associated with malabsorption such as coeliac disease, Crohn's disease, and cystic fibrosis. Vitamin B12 may also be used to help diagnose the cause of mental or behavioural changes, especially in the elderly.
In patients with known vitamin B12 and folate deficiencies, these tests may be used occasionally to help monitor the effectiveness of treatment. This is especially true in patients who cannot absorb vitamin B12 and/or folate and must have lifelong treatment.
Vitamin B12 and folate are primarily measured when a FBC, done routinely or as part of an evaluation of anaemia, indicates the presence of large red RBCs.
When a person, especially an elderly person, exhibits mental or behavioural changes such as irritability, confusion, depression and/or paranoia, vitamin B12 may be requested to help diagnose the underlying cause. They may also be used when a patient has physical symptoms that suggest B12 or folate deficiency, including dizziness, weakness, fatigue, or a sore mouth or tongue.When a patient has symptoms suggesting nerve damage or impairment, such as, numbness or abnormal sensations in the toes or fingertips and weakness or clumsiness in the hands or feet, a vitamin B12 test may be requested to help diagnose the cause and to detect the presence of a vitamin B12 deficiency.
B12 and folate may sometimes be requested when a patient shows signs of malnutrition or malabsorption or is known to have a disorder that affects nutrient absorption. When a breastfed infant has a vitamin B12 or folate deficiency, the mother may also be tested to see if she has a deficiency that is affecting both her and her child.
When a patient is being treated for vitamin B12 or folate deficiency, they may occasionally be monitored to evaluate the effectiveness of the treatment. In a person with a nutritional deficiency, this may be done as a follow-up to treatment. In a person with a condition causing a chronic deficiency, this may be part of a long-term treatment plan.
The doctor is looking for vitamin B12 and/or folate deficiency. If a symptomatic patient has decreased concentrations of vitamin B12 and/or folate, then it is likely that he has some degree of deficiency. The test results indicate the presence of deficiency, but do not necessarily reflect the severity of the anaemia or neuropathy associated with the deficiency.
It is possible to have low B12 or folate levels on blood tests without any clinical problems. In the case of B12 measurements, this partly reflects a weakness in the standard B12 blood test (also called serum cobalamin) which does not directly measure whether there is an actual deficiency of active vitamin B12 in the cells of the body. Second-line tests that might help determine true deficiency include plasma methylmalonic acid and plasma homocysteine. Serum holotranscobalamin (also referred to as ‘active’ B12) has the potential as an alternative first-line test, but some uncertainty may still exist. The availability of these second-line tests is currently very limited.
If a patient with a vitamin B12 or folate deficiency is being treated with oral supplements (or with intramuscular B12 injections), then normal or elevated results indicate a response to treatment. It is not standard practice to monitor patients having regular B12 injections.
High levels of B12 and folate are not usually monitored. Increased B12 may be seen in conditions such as leukemia or liver dysfunction. Increased folate may be seen with pernicious anaemia, vegetarian diets, or with a condition called bacterial overgrowth syndrome where bacteria multiply in the upper bowels.
If a patient is deficient in both vitamin B12 and folate, but only takes folic acid supplements, the vitamin B12 deficiency may be masked. The anaemia associated with both may be resolved, but the underlying neuropathy (nerve damage) will persist and may deteriorate.
The Schilling test was once used fairly routinely to confirm a diagnosis of pernicious anaemia as the cause of a vitamin B12 deficiency by demonstrating abnormal B12 absorption in the small intestine. It is no longer widely available. The Schilling test has been replaced, in part, by the measurement of intrinsic factor binding antibodies although these may only be seen in about 50% of patients with pernicious anaemia.
B12 levels may be reduced in women taking oestrogen containing oral contraceptives and in pregnancy, however this does not necessarily reflect a true deficiency of the vitamin in the body, demonstrating that the standard B12 laboratory test can be unreliable under some circumstances.
This article was last reviewed on 13 June 2016. | This article was last modified on 13 June 2016.
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