Q. Would you put a patient on blood-pressure medication if her at-home readings are below 120/80 but test higher at her doctor's office? And don't certain pills worsen cholesterol?

A. As many as 20 percent to 35 percent of patients diagnosed with hypertension have blood pressure above 140/90 in the doctor's office but normal readings outside the office. It's what is known as white-coat hypertension. Experts regard a home pressure of less than 135/85 as being normal.

According to the latest guidelines for hypertension treatment (the Joint National Committee Seven), if out-of-office pressures are consistently less than 130/80, then drug therapy can be avoided even with elevated pressures in the doctor's office, as long as there is no evidence of damage from high blood pressure. Damage from hypertension includes strokes, heart attacks, heart failure, increased heart thickness, kidney disease, and arterial disease in the legs.

However, this assumes that the person in question is checking his or her pressures correctly with a machine that's accurate. In a study of blood-pressure devices, only five of 24 devices tested passed.

Before buying a blood-pressure device, see www.dableducational.com/sphygmomanometers/devices_2_sbpm.html#ArmTable to find one that's accurate. Avoid finger or wrist cuffs, which are inaccurate. Get an automated arm device, preferably one that has a memory that can record pressures for the doctor. The cuff bladder width should be at least 40 percent of the arm circumference (big patients will need wider cuffs, otherwise the pressure will read too high).

In the obese, the doctor may need to measure pressure from a cuff placed on the forearm and listen over the wrist. Devices are not usually accurate in patients with an irregular or slow pulse. Calibrate the machine once a year. Don't record measurements taken the first day you try the device, as these are generally inaccurate. Take pressures twice in the morning and twice in the evening for three consecutive days to get your baseline pressure. If one of your arms regularly has higher pressures, then use this arm, as it reflects your true blood pressure.

And, yes, certain pills may worsen cholesterol, but this is not considered clinically significant. Studies longer than one year using usual doses of diuretics generally have not shown increased cholesterols. By treating high blood pressure, you will reduce risk of stroke 35 percent to 40 percent, risk of heart attacks 20 percent to 25 percent, and risk of heart failure by more than 50 percent. And even in the elderly, the goal should be less than 140/90 if at all possible, and 130/80 or less in those with diabetes or kidney disease. (Subtract 5 from these numbers for home measurements).

Dr. Landis Lum is a family-practice physician for Kaiser Permanente and an associate clinical professor at the University of Hawai'i's John A. Burns School of Medicine. Send your questions to Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; fax 535-8170; or write islandlife@honoluluadvertiser.com. This column is not intended to provide medical advice.