DEAR DR. DONOHUE: I am a 79-year-old male in fairly good health. I do have hypertension, and had two bladder cancers, which were found early and removed.

My lingering problem is low potassium. My doctor does not have any idea why my kidneys are dumping potassium, so I hope you might have a suggestion. My potassium has never been above 3.1.

I take only three drugs: Toprol, diltiazem and potassium chloride. — E.W.

ANSWER: The normal blood potassium level lies between 3.5 and 5 mEq/L (or mmol/L). Symptoms from low potassium aren’t usually seen until the blood level drops below 3.0. Potassium has many roles to play. It’s involved in the synthesis of proteins and carbohydrates. It has a positive charge, which maintains the body’s electrical balance against negatively charged elements. It’s involved in the transmission of nerve signals. It’s also involved in heart action.

A drop in potassium brings on muscle weakness, muscle cramps, abnormal heartbeats and a rise in blood pressure.

The most common cause of low potassium is water pills, diuretics. Most of them increase the kidneys excretion of potassium. You aren’t taking a diuretic, so that possibility doesn’t hold true for you. Diarrhea and vomiting also lead to a depletion of potassium. Adrenal gland overproduction of its hormones brings on a potassium loss and also raises blood pressure. That could explain both your hypertension and low potassium. Magnesium deficiency has a hand in lowering potassium. Chewing large quantities of licorice containing glycyrrhetinic acid lowers potassium. (Not all licorice contains that material. It will be listed on the label if the licorice does.) Some kidney disorders cause potassium loss.

Your question doesn’t lend itself to an easy answer. Low potassium is a complicated issue best unraveled by lab tests. Only your doctor can obtain that information for you.

DEAR DR. DONOHUE: I would appreciate if you would describe PKU. I believe it has something to do with protein. — S.M.

ANSWER: PKU isn’t a protein. It’s phenylketonuria (FEE-nul-KEY-tone-YOUR-ee-uh), an inherited deficiency of an enzyme that degrades the amino acid phenylalanine. A buildup of phenylalanine leads to brain damage. PKU is a genetic condition involving two genes, one from the mother and one from the father.

Babies with PKU often have a musty odor, a fair complexion and are subject to having seizures. The worst complication is lack of brain development.

Most countries test for PKU in all babies. Once discovered, successful treatment is accomplished with a diet limiting the amount of phenylalanine foods.

DEAR DR. DONOHUE: A couple of times after having a bowel movement, I noticed some bleeding. My wife insisted that I see our family doctor. He thinks the bleeding is coming from a small hemorrhoid, but he referred me to a specialist for a colonoscopy.

I am 67. I have no other symptoms. Is this necessary? I don’t relish the idea. — P.B.

ANSWER: Everyone is supposed to have a colonoscopy at age 50. It’s the best way of detecting colon cancer.

Colonoscopy isn’t the dreadful experience you imagine. Most patients are put into a sleepy state and feel no discomfort.

You should jump at the chance. It’s the best way to find out where the blood is coming from, and you get the additional benefit of discovering the initial stages of colon cancer — if they are there. Colon cancer is silent, in most cases, until it has grown large and spread.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.

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