Some medications for high blood pressure can actually end up raising blood pressure in certain patients. In a study from Albert Einstein College of Medicine, nearly 8% of the study participants saw their blood pressure go up by 10 points or more after taking a blood pressure drug. The good news is that the study found a blood test that helps predict who is most likely to have their blood pressure rise while on the medications.

The blood test measures people's renin level. Renin is an enzyme produced by the body that tends to narrow blood vessels. A high renin level can be a cause of high blood pressure.

There are many different causes of high blood pressure and many different classes of medication to treat it.

In the study, the subjects likeliest to see a large blood pressure rise were those with a low renin level who were prescribed a beta blocker or ACE inhibitor.

There are many different causes of high blood pressure and many different classes of medication to treat it. Some drugs lower blood pressure by lowering blood volume. This is how diuretics and calcium channel blockers work. Collectively, they are called V-drugs. Other drugs lower blood pressure by widening blood vessels. They do this by weakening the effects of renin or other substances that renin interacts with. Beta blockers and ACE inhibitors work in this fashion and are called R-drugs.

The study showed that subjects with a high renin level were likeliest to benefit from taking an R-drug, while those with a low renin level were likeliest to benefit from taking a V-drug. This suggests that renin testing could help in selecting the best class of blood pressure medicine to prescribe and that patients with high blood pressure should have their renin level tested before being prescribed a blood pressure drug.

The study was performed on 945 subjects who had enrolled in a workplace blood pressure reduction program in New York City between 1981 and 1988. At the start of the study, all subjects had a systolic blood pressure of 140 or higher and had not been taking any blood pressure medication. An R-drug (beta blocker or ACE inhibitor) was prescribed to 537 of the subjects and a V-drug (diuretic or calcium channel blocker) to the other 408 subjects.

Blood pressure measurements and blood samples were taken before subjects began taking medication and again upon revisit to the treatment center, 30-90 days later.

Overall, 7.7% of the subjects showed a blood pressure increase of 10 points or more upon revisit. But when subjects were grouped according to their measured blood renin level (high, medium or low), the researchers found that fully 18% of the group with low renin that had been taking an R-drug showed a 10 point or higher blood pressure increase. This was the largest percentage found in any of the six groups.

This suggests that people with low renin should not be prescribed an R-drug.

Often, blood pressure patients need to take multiple drugs before their blood pressure gets under control. Renin testing might lower the number of drugs such patients need to take by suggesting which drugs are unlikely to work.

In the past, tests for blood renin were both expensive and of questionable accuracy. They have become more accurate and cheaper in the last few years. The study suggests that a renin test could help predict the best blood pressure medication to prescribe to a patient and help prevent the situation where a patient takes a drug for high blood pressure and ends up with an even higher blood pressure.

An article detailing the study appears in the September 2010 issue of the American Journal of Hypertension.