Study: Low BP levels are unhealthy for CKD patients

Recent guidelines by The National Kidney Foundation Disease Outcomes Quality Initiative (NKF KDOQI)1 call for lower target blood pressure levels in patients with chronic kidney disease (CKD). But in the absence of high-quality scientific evidence, there's a chance this recommendation could do more harm than good, according to a special article appearing in an upcoming issue of the Journal of the American Society Nephrology (JASN).

"The new low blood pressure goals are not definitively supported by data, would be costly to the healthcare system and potentially harmful to patients," according to Julia B. Lewis, MD (Vanderbilt University, Nashville, TN), who performed a critical review of the research evidence.

Issued last year, updated national guidelines for CKD treatment call for a target blood pressure level of less than 130/80 mm Hg (millimeters of mercury) to help preserve kidney function. The recommendation was based on observational studies showing "a continuous benefit of reducing blood pressure to lower and lower levels."

However, Lewis points out several problems with the research behind the new guidelines. Most importantly, since patients in the observational studies were not randomly assigned to different blood pressure goals, the apparent benefit of lower blood pressures could result from other "confounding" factors. "The data supporting the current blood pressure guidelines for patients with CKD do not meet the standard of a primary outcome of a randomized trial," says Lewis.

She explains that, as kidney disease worsens, blood pressure rises and becomes harder to control. So the data may simply reflect the fact that patients with less severe kidney disease have lower blood pressure. In studies where patients were randomly assigned to treatments, the benefits of lower blood pressure were seen only in a subgroup of patients, or several years after the end of treatment.

"Also there is other evidence to bring into question the widespread application of this costly goal of a blood pressure less than 130/80 mm Hg," Lewis adds. Some studies have even suggested that CKD patients with very low blood pressure could be at increased risk of death.

A new trial sponsored by the National Institutes of Health (NIH) will compare the effects of different blood pressure targets in over 10,000 patients with CKD. Until the results are available, Lewis believes that doctors should make individualized decisions about blood pressure control for their patients with kidney disease.

Lewis emphasizes that no firm conclusions can be drawn from her review, since it was based on different types of studies with conflicting results.

The article, entitled "Blood Pressure Control in Chronic Kidney Disease: Is Less Really More?" will appear online at http://jasn.asnjournals.org/ on June 24, 2010, doi 10.1681/ASN.2010030236.