A vitamin B-12 level test checks the amount of vitamin B-12 in the blood or urine to gauge the body's overall vitamin B-12 stores.  Vitamin B-12 is necessary for several bodily processes, including nerve function and the production of DNA and red blood cells.

A person whose vitamin B-12 levels are outside of the normal range will require treatment. Low levels of the vitamin can cause neurological symptoms, as well as fatigue, constipation, and weight loss. High B-12 levels may indicate liver disease, diabetes, or another condition.

Individuals with low vitamin B-12 levels often require regular injections of the vitamin. These shots are more effective than supplements at raising vitamin B-12 levels, especially when people have medical conditions that may make it more difficult to absorb supplements.

For some people, high doses of vitamin B-12 supplements may improve B-12 status. Supplements are available in capsule or liquid form from pharmacies, supermarkets, health stores, and online. It may also be helpful to eat more foods that are rich in vitamin B-12.

Methionine is an amino acid. Amino acids are the building blocks that our bodies use to make proteins. Methionine is found in meat, fish, and dairy products, and it plays an important role in many cell functions.

Methionine is used to prevent liver damage in acetaminophen (Tylenol) poisoning. It is also used for increasing the acidity of urine, treating liver disorders, and improving wound healing. Other uses include treating depression, alcoholism, allergies, asthma, copper poisoning, radiation side effects, schizophrenia, drug withdrawal, and Parkinson's disease.