Test used to diagnose B12 deficiency may be inadequate

A test that generally is used to measure the amount of vitamin B12 in the body is not sensitive enough to detect a deficiency of the vitamin, which has been linked to several neurological conditions, according to Saint Louis University research.

The findings were presented this month at a meeting of the American Neurological Association.

"B12 deficiency is associated with dementia, peripheral neuropathy and spinal cord disease," says Florian Thomas, M.D., Ph.D., associate professor of neurology at Saint Louis University School of Medicine and a researcher on the project.

"While it occurs at any age, B12 deficiency is more common in the elderly, may affect some vegetarians and their newborns, can be provoked by laughing gas anesthesia and also by a unique form of recreational drug use. Importantly, it is very easy to treat by taking one pill per day for life. We need to do a better job of detecting the problem."

Thomas and his Saint Louis University colleagues, Laurence J. Kinsella, M.D., associate professor of neurology, and Jamie T. Haas, M.D., a neurology resident, found that the standard test for B12 deficiency -- measuring its blood level -- may be too insensitive.

The scientists found that of 34 patients who had normal levels of B12, 26 had elevated levels of methylmalonic acid (MMA), which indicated B12 deficiency.

They are urging doctors who suspect their patients lack the vitamin to also test for levels of MMA, a natural compound in the body that increases when B12 is lacking.

"The usual way of diagnosing B12 deficiency may be inadequate because it underestimates the frequency of the problem, which is present in up to 20 percent of the elderly," Thomas says. "The problem is eminently treatable at pennies a day."

Dr. Kinsella has had a longstanding interest in B12 deficiency and its relationship to nitrous oxide, a general anesthetic in common use in dental offices and hospital operating rooms. A B12 deficiency can be caused by nitrous oxide, also known as laughing gas, by inhibiting the action of B12 when tissue stores are low.

"This becomes a public health problem in the elderly undergoing surgery or dental work who may have undiagnosed and untreated B12 deficiencies. It also occurs among dental personnel and others who repeatedly abuse nitrous oxide for its euphoric effects," he says.

Nitrous oxide abuse in the form of "whippets" or "whippits" occurs among medical personnel, teenagers and young adults who purchase nitrous oxide containers from baking supply stores or use the gas contained in whipped cream dispensers (hence the name), says Kinsella.

Thomas and colleagues earlier this year published the case of a young man who abused nitrous oxide and devastating neurological damage to the spinal cord and peripheral nerves. The link to nitrous oxide was recognized and the patient recovered with B12 replacement.

B12 deficiency also can be a consequence of stomach stapling bariatric surgery, which has become an increasingly common procedure for weight loss, because an intact stomach is important for B12 absorption, Thomas says.

Multiple sclerosis can be difficult to distinguish from B12 deficiency, cautioned a companion piece also presented at the conference.

Saint Louis University researchers Chitharanjan Rao, M.D., neurology resident, John Selhorst, M.D., chair of neurology, and Thomas found that patients with either condition can have pain, problems with vision and gait and similar MRIs.

The potential confusion makes careful search for B12 deficiency even more critical, Thomas says, since B12 deficiency can easily be reversed, while multiple sclerosis may be a life-long disease.

Thomas and Kinsella urge doctors to more rigorously check for B12 deficiency by measuring both serum B12 and MMA in patients before surgery and to test patients who are over 65 for the problem every two years. Nitrous oxide abuse resulting in B12 deficiency should be considered especially in younger adults presenting with unusual neurological conditions.