Diastolic blood pressure below 70 mm Hg associated with higher mortality in chronic kidney disease

Achieving ideal systolic blood pressure (SBP) at the expense of lower-than-ideal diastolic blood pressure (DBP) could be harmful in adults with chronic kidney disease (CKD), noted a study.

A review of U.S. veterans with CKD found that SBP of 130 to 159 mm Hg and DBP of 70 to 89 mm Hg were associated with the lowest mortality rates.

Researchers looked at a retrospective cohort of 651,749 U.S. veterans with non-dialysis-dependent CKD and more than 18.5 million blood pressure measurements at all U.S. Department of Veterans Affairs health care facilities between 2005 and 2012.

All possible combinations of SBP and DBP were examined in 96 categories from lowest (<80/<40 mm Hg) to highest (>210/>120 mm Hg), in 10-mm Hg increments.

Results appeared in the Aug. 20 Annals of Internal Medicine.

Patients with SBP of 130 to 159 mm Hg combined with DBP of 70 to 89 mm Hg had the lowest adjusted mortality rates, and those in whom both SBP and DBP were concomitantly very high or very low had the highest mortality rates, researchers wrote. Patients with moderately elevated SBP combined with DBP no less than 70 mm Hg had consistently lower mortality rates than did patients with ideal SBP combined with DBP less than 70 mm Hg. Results were consistent in subgroups of patients with normal and elevated urinary microalbumin-creatinine ratios.

The researchers noted that paradigms emphasize treating the higher of the SBP or DBP readings, which ignores the potential negative effects of low pressures that are linked with their normal or elevated counterparts. In addition, they said, it is common in CKD for patients to have elevated SBP combined with low DBP.

They wrote, "Nearly one third (32.5%) of the patients in our cohort had SBP greater than 140 mm Hg and DBP less than 70 mm Hg at some point during the observation period. Our granular analyses of BP categories indicated that categories of lower SBP–DBP combinations are associated with lower mortality rates only as long as the DBP component remains greater than approximately 70 mm Hg."

An editorial noted that the observational data do not address causality and that "remarkable attenuation" in the adjusted analyses raises the specter of residual confounding.

The editorial stated, "It may not be the BP combination per se but the characteristics of the persons with that combination that lead to greater mortality rates. Also, the assumption outlined previously and implied by [the study authors] (that DBP and SBP move in tandem with treatment) may not necessarily be the case. Translating these findings into practice is challenging."