From the Guidelines
Methotrexate can indeed interfere with vitamin B12 level measurements, potentially leading to falsely elevated results. This interference is crucial to recognize, especially in patients undergoing methotrexate therapy for conditions such as rheumatoid arthritis, psoriasis, or certain cancers, as it may mask an actual vitamin B12 deficiency 1. The mechanism behind this interference is related to methotrexate's structural similarity to folate, which is closely linked to vitamin B12 metabolism, thereby causing analytical interference in the testing methods.
Key Considerations
- Methotrexate's impact on folate levels is well-documented, and its effect on vitamin B12 measurements is a significant concern in clinical practice 2, 1.
- Patients on methotrexate who show unexpectedly high B12 levels but exhibit symptoms suggestive of B12 deficiency, such as fatigue, neurological symptoms, or macrocytic anemia, should undergo alternative testing methods.
- Alternative testing methods like methylmalonic acid or homocysteine levels are not affected by methotrexate interference and can provide a more accurate assessment of vitamin B12 status.
- Ideally, B12 levels should be measured before starting methotrexate therapy to establish a baseline or after a sufficient washout period if clinically appropriate, to ensure accurate monitoring and management of potential deficiencies.
Clinical Implications
- Healthcare providers should be aware of the potential for methotrexate to interfere with vitamin B12 level measurements and take this into consideration when interpreting laboratory results for patients on this medication.
- The treatment of vitamin B12 deficiency, especially in the context of methotrexate therapy, should follow established guidelines, which may include hydroxocobalamin administration and monitoring of methylmalonic acid or homocysteine levels 1.
From the Research
Methotrexate and Vitamin B12 Interaction
- Methotrexate is known to interfere with vitamin B12 metabolism, potentially leading to vitamin B12 deficiency 3, 4, 5.
- However, there is no direct evidence to suggest that methotrexate falsely elevates vitamin B12 levels.
- Studies have shown that methotrexate can cause malabsorption of vitamin B12, leading to deficiency 3.
- Vitamin B12 deficiency can also exacerbate methotrexate toxicity, leading to severe complications such as pancytopenia and hepatotoxicity 4, 5.
Effects of Methotrexate on Vitamin B12 Levels
- One study found that plasma vitamin B12 levels were similar between patients with rheumatoid arthritis treated with methotrexate and folic acid and those treated with other therapies 3.
- Another study suggested that vitamin B12 deficiency may contribute to methotrexate toxicity, and that testing for vitamin B12 deficiency is important in patients with rheumatoid arthritis and macrocytic anemia 5.
- Vitamin B12 has been shown to have a protective effect against methotrexate hepatotoxicity, with supplementation improving outcomes in animal studies 6.
Clinical Implications
- Patients treated with methotrexate should be monitored for vitamin B12 deficiency, particularly those with risk factors such as malabsorption or pernicious anemia 3, 5.
- Vitamin B12 supplementation may be necessary to prevent deficiency and reduce the risk of methotrexate toxicity 5, 6.
- Further studies are needed to fully understand the interaction between methotrexate and vitamin B12 and to determine the optimal approach to monitoring and managing vitamin B12 levels in patients treated with methotrexate 3, 5.