From the Guidelines
Vitamin deficiency labs should be ordered based on clinical suspicion from symptoms like fatigue, neurological changes, poor wound healing, or bleeding tendencies, and should include tests such as vitamin B12, folate, vitamin D, vitamin A, vitamin E, and vitamin K, as well as iron studies and complete blood count. When evaluating vitamin deficiencies, it is essential to consider the clinical context and potential limitations of the tests, such as the effect of seasonal variation on vitamin D levels and the impact of acute inflammation on certain vitamin markers 1. The diagnosis of iron deficiency, for example, can be complicated by the presence of inflammation, and a combination of parameters such as ferritin, transferrin saturation, and transferrin receptor concentrations should be assessed to determine the exact type of anemia 1. In patients with symptoms suggestive of vitamin B12 deficiency, testing should focus on symptoms and signs commonly attributed to vitamin B12 deficiency, where testing is likely to identify people with a clinical deficiency and a diagnosis is most likely to be achieved 1. Key laboratory tests for vitamin deficiencies include:
- Vitamin B12 and folate (measured via serum levels and methylmalonic acid or homocysteine for B12 functional status)
- Vitamin D (measured as 25-hydroxyvitamin D)
- Vitamin A (retinol)
- Vitamin E (alpha-tocopherol)
- Vitamin K (prothrombin time)
- Iron studies (ferritin, iron, TIBC)
- Complete blood count to assess for macrocytic anemia in B12 or folate deficiency. Testing should be targeted rather than performed as general screening in asymptomatic individuals without risk factors, and treatment depends on the specific deficiency identified and may involve oral supplementation or, in severe cases, injectable forms like B12 injections for pernicious anemia 1.
From the FDA Drug Label
Laboratory Tests During the initial treatment of patients with pernicious anemia, serum potassium must be observed closely the first 48 hours and potassium replaced if necessary Hematocrit, reticulocyte count, vitamin B12, folate and iron levels should be obtained prior to treatment. The following lab tests are recommended for patients with pernicious anemia:
- Hematocrit
- Reticulocyte count
- Vitamin B12
- Folate
- Iron levels These tests should be obtained prior to treatment and repeated as necessary to monitor the patient's response to therapy 2.
From the Research
Vitamin Deficiency Labs
- Vitamin D deficiency can be identified through laboratory tests, specifically a 25-hydroxyvitamin D level 3
- Deficiency is defined as a serum 25-hydroxyvitamin D level of less than 20 ng per mL (50 nmol per L), while insufficiency is defined as a serum 25-hydroxyvitamin D level of 20 to 30 ng per mL (50 to 75 nmol per L) 3
- Common manifestations of vitamin D deficiency that may prompt lab testing include:
- Symmetric low back pain
- Proximal muscle weakness
- Muscle aches
- Throbbing bone pain elicited with pressure over the sternum or tibia 3
- Treatment goals include normalizing vitamin D levels to relieve symptoms and decrease the risk of fractures, falls, and other adverse health outcomes 3
- Prevention and treatment strategies may involve vitamin D supplementation, with recommended dosages varying by age and deficiency status 3