Background: Vitamin B12 deficiency is a critical medical condition that, if left untreated, can lead to severe symptoms and potentially serious and life-threatening complications. Clinical guidelines are designed to provide a standardized approach to diagnosis and treatment, aiming for consistency and effectiveness. However, it is well-established that not all patients fit into general guidelines. Objective: To investigate the clinical relevance of the submitted research to support these protocols for diagnosing and treating a B12 deficiency. Approach: Conducting a literature review of the references focused and used on diagnosing and treating vitamin B12 deficiency in adults and children. Results: No robust clinical trial nor RCT has been found to back up the current protocols. The research used is primarily based on assumptions rather than solid clinical evidence. Conclusion: Existing guidelines for vitamin B12 deficiency need to be significantly revised and improved through clinical research, clinical experience by experts in the field with input from patient groups worldwide.