Dear Dr. Roach: I recently read in your column that you test your patient’s magnesium levels when they have been on longterm proton-pump inhibitors (PPIs). When I asked my doctor to include this in his order for blood tests, I was told that the test isn’t accurate, and he wouldn’t order it. Is there a special magnesium test that I can request?

When I looked it up on the internet, this is what I found: “Standard magnesium blood tests (serum) are generally not considered an accurate indicator of total body magnesium. While they can detect severe deficiency, they are unreliable for diagnosing mild-to-moderate deficiencies because less than 1% of the body’s magnesium resides in the blood, with levels tightly controlled by borrowing from bones.” — J.B.

Answer: Although many clinicians do test their patients for low magnesium when they are on long-term PPIs like omeprazole, this isn’t a standard guideline. The expert societies don’t recommend testing magnesium levels, although the Food and Drug Administration recommends that clinicians “consider” checking magnesium levels prior to starting therapy, as well as periodically during treatment.

People who are on PPIs and most diuretics are at a high risk for low magnesium. It’s true that most magnesium is in the cells; however, like potassium and calcium, a low blood level does indicate that the body level is also low, and steps should be taken to keep the body from losing more magnesium.

Although there are people who need long-term PPIs, such as those with Barrett’s esophagus or those in whom tapering off PPIs has failed, my experience is that there are many people who are taking these medicines who may not need them. I am sure that they were started on them for a good reason, but most people can be tapered off the medicine after six weeks or so.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu.