DEAR DR. DONOHUE: I have a blood-pressure-control problem. I am at maximum strength on my current medicines, and my blood pressure still remains high. My doctor suggests a kidney circulation test, which could reveal the need for a stent to lower the pressure. This is something new to me. I would appreciate your comments. – E.K.

ANSWER: Most high blood pressure is essential hypertension, which means that it’s high blood pressure not brought on by a separate process that’s going on in the body. A narrowed kidney artery is an example of such a separate process.

The kidney produces an enzyme called renin. Renin turns another body substance, angiotensin, into an active compound that constricts arteries throughout the body and raises blood pressure. It also causes salt retention, another factor in raising blood pressure.

Kidneys make renin for a good reason. When blood pressure drops, they sense the drop and release renin to maintain normal pressure. However, if a kidney has a narrow artery, the kidney is fooled into thinking that body blood pressure is low, and it puts out renin when it shouldn’t. The resulting high blood pressure is called renovascular hypertension – “reno” for “kidney” and “vascular” for “artery.”

This kind of high blood pressure is secondary high blood pressure – secondary to a distinct body malfunction. Doctors think of causes for secondary high blood pressure when blood-pressure medicines fail to control pressure or when pressure appears at young ages.

A narrowed kidney artery often produces a noise the doctor can hear when listening to the abdomen with a stethoscope. Special scans show it. Sampling the kidney’s vein for increased levels of renin confirms the suspicion of renovascular hypertension. Putting a stent in the narrowed artery – the same kind of stent used to open a narrowed heart artery – can often end renovascular hypertension without having to use drugs.

Readers who would like a more complete discussion of high blood pressure can obtain the booklet on that topic by writing: Dr. Donohue – No. 104, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6.75 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: My blood pressure sometimes runs slightly over 140/70. I had an allergic reaction to the blood-pressure pill my doctor prescribed. He doesn’t want me on another pill unless my systolic pressure is over 145 or my diastolic is over 90. I do take a water pill. Should I be on a blood-pressure pill? – L.M.

ANSWER: You are on a blood-pressure pill – a water pill. It’s often the first medicine prescribed for elevated blood pressure.

You don’t need a second medicine. If the systolic pressure – the first number – lies between 140 and 159 and the diastolic pressure – the second number – is less than 90, more medicine is not needed. Some doctors treat such blood pressure only with a low-salt diet, exercise and weight loss unless these people have other risk factors for heart disease.

DEAR DR. DONOHUE: Our daughter has obsessive-compulsive disorder, depression and anorexia. I feel she needs to be on medication. She resents it when I talk to her about it. She and her husband feel all this is a disgrace and that medicine is too expensive. Please comment. – Anon.

ANSWER: Your daughter’s problems are not a disgrace and are not shameful. They are not character flaws. They spring from a glitch in brain chemistry and in communication between brain cells. She and her husband are making a tragic mistake by not getting professional help. She’s not likely, on her own, to overcome these illnesses. A professional needs to intervene.

Medicines are important to restoring normal brain chemistry. I hope she and her husband will listen to you and me.

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.