Prescription drugs taken to control hypertension could actually boost blood pressure among patients as a result of a mismatch between a person's plasma renin activity (PRA) and the medication, a new study has revealed.

PRA is a measure of the activity of the plasma enzyme renin, which plays a major role in the body's regulation of blood pressure, thirst, and urine output. The study was conducted by a team of researchers at the Albert Einstein College of Medicine of Yeshiva University in New York.

The study, which appeared in the online edition of the American Journal of Hypertension, related to 945 residents of New York who took part in a program designed to control hypertension at the workplace that was carried out between 1981 and 1998.

Dr. Michael Alderman, a professor of epidemiology & population health at the Albert Einstein College, who led the research team, said that doctors are aware of a varied response to anti-blood pressure treatment whereby some patients show an elevation in the reading.

"The latter phenomenon is generally attributed to patients' failure to take their medications or to a random event. But these data show that it's not a random event," he says in a news release issued by the American Society of Hypertension.

The participants, none of whom had undergone treatment for hypertension prior to enrolling in the study but had systolic blood pressure, were prescribed either of two types of medications - a "V" drug to lower blood volume or an "R" drug to lower the kidney enzyme renin that is critical to blood pressure control.

After reviewing the data related to PRA and systolic blood pressure levels during the treatment, the researchers found that the PRA levels actually helped decided which of the two drug forms could result in a patient facing problems.

Patients who had low renin levels and took the "R" drug showed a spurt in blood pressure. More than 70 percent of the group of volunteers displayed a significant increase in blood pressure.

Our findings suggest that physicians should use renin levels to predict the most appropriate first drug for treating patients with hypertension. Our data indicate that patients with low PRA values are at highest risk of a clinically significant increase in systolic blood pressure when prescribed an R drug, the researchers said.

They concluded that tracking renin levels would be helpful among two groups of patients - those taking BP medications for the first time and those already on a regimen incorporating many anti-hypertension drugs.