Vitamin B12 is a nutrient the body needs for various functions, including making new blood cells, supporting healthy nerve cells, and creating DNA. Healthcare providers often recommend B12 testing to identify a deficiency, monitor existing conditions, or assess the effectiveness of treatment.
Understanding B12 Testing and Accuracy
B12 tests primarily measure the amount of vitamin B12 circulating in your blood, known as serum B12 levels. While serum B12 is a common measure, healthcare professionals may also consider other markers like methylmalonic acid (MMA) and homocysteine. Elevated levels of MMA and homocysteine can indicate a B12 deficiency, even if serum B12 appears to be within a low-normal range, as these substances build up when B12 is not functioning effectively.
When individuals take B12 supplements, these supplements can artificially increase the B12 levels in the bloodstream. This elevation can mask an underlying deficiency, making it difficult for healthcare providers to assess the body’s natural B12 status and determine the true need for supplementation or further investigation. Therefore, temporary cessation of supplements before testing is often advised.
Specific Guidelines for Stopping B12 Supplements
The general advice for discontinuing B12 supplements before a blood test typically ranges from a few days to several months, depending on the specific circumstances. Many sources suggest stopping for at least a week to a month before the test. Some recommendations advise a shorter break of 2 to 7 days for water-soluble vitamins like B12 to allow for excretion.
It can take around three months for traces of extra B12 to disappear from the blood, regardless of whether it was taken orally, sublingually, or via injection. Some guidelines even recommend clearing B12 supplements for at least four months before testing serum B12, particularly because inactive forms of B12 can remain in the blood for an extended period and skew results.
The duration for stopping can also depend on the dosage and form of the supplement. High-dose supplements or B12 injections might require a longer washout period compared to lower-dose oral or sublingual forms, or B12 obtained from multivitamins. It is important to discuss these specific details with a healthcare provider, as they can provide personalized instructions based on individual health status and the reason for the test.
Other Factors Affecting B12 Test Results
Beyond B12 supplements, several other factors can influence the accuracy of B12 test results. Certain medications are known to affect B12 levels or its absorption. For instance, metformin, a common medication for type 2 diabetes, has been shown to decrease B12 levels, especially with higher doses and longer treatment durations. Proton pump inhibitors (PPIs), used to reduce stomach acid, can also interfere with B12 absorption over time, potentially leading to lower levels. Histamine H2 blockers, another class of acid-reducing drugs, can also impact B12 absorption.
Underlying health conditions also play a role in B12 status and test interpretation. Conditions affecting the digestive system, such as gastritis, Crohn’s disease, and celiac disease, can impair the body’s ability to absorb B12 from food. Pernicious anemia, an autoimmune condition where the body cannot produce intrinsic factor needed for B12 absorption, is a common cause of B12 deficiency. Additionally, kidney disease or certain liver conditions can sometimes lead to altered B12 levels, potentially showing elevated readings that do not reflect true B12 availability.
Post-Test Actions and Next Steps
Once the B12 blood test is complete, it is generally safe to resume taking B12 supplements unless your healthcare provider advises otherwise. The primary purpose of stopping them was to obtain an accurate baseline measurement. If you were taking supplements as part of a prescribed treatment, your provider will guide you on when and how to restart.
The next step involves discussing the test results with a healthcare professional. Interpreting B12 levels involves considering the specific values, the type of test performed (e.g., serum B12, MMA, homocysteine), and individual health history and symptoms. A healthcare provider can explain what the results mean in the context of your overall health. They will determine if the levels indicate a deficiency, sufficiency, or other underlying issues. Based on this comprehensive evaluation, your doctor will develop a personalized treatment plan, which might include dietary changes, continued supplementation, or further diagnostic tests; self-diagnosis or self-treatment based solely on test results is not recommended.