Strict blood pressure control in kidney disease linked to worse outcomes

1. Among patients with chronic kidney disease, a goal systolic blood pressure between 120-139 mmHg was associated with a lower mortality rate than a stricter goal systolic blood pressure of less than 120 mmHg. 

2. This mortality benefit remained even in sub-group analyses, in which investigators compared the two different blood pressure groups among patients with different comorbidities, such as diabetes, coronary artery disease, and heart failure. 

Evidence Rating Level: 2 (Good)            

Study Rundown: Blood pressure recommendations are often made on the basis of clinical trials. However, these trials often exclude patients with chronic kidney disease (CKD), so results cannot be generalized to this population As a result, the goal blood pressure for these patients is often determined by expert opinion, such as in the Eight Joint National Committee (JNC 8) guideline, rather than study data. This study was carried out to determine the effect of blood pressure control in patients with CKD. The results suggested that patients with CKD who had a higher systolic blood pressure (SBP) of 120-139 mmHg had a mortality benefit over a lower SBP of less than 120 mmHg. This benefit remained even when patients with comorbidities such as diabetes, coronary artery disease, and heart failure, were compared between the two groups.

The relatively large size of the cohort is a major strength of the study. In addition, the investigators used mortality rather than an indirect marker of survival, which increases the clinical significance and applicability. However, since the study was observational, there were inherent differences between the two groups, which could have accounted for the mortality difference more than the SBP. Investigators attempted to control for this by using a well-validated propensity matching technique to create two cohorts with no demographic differences aside from the SBPs. Other characteristics of the study that add uncertainty to the results include using ICD9 codes to determine co-morbid conditions, which are not always reliable, and the predominance of male patients, which decreases generalizability to female patients.

Click to read the study, published today in JAMA Internal Medicine

Relevant Reading: Blood pressure and mortality in U.S. veterans with chronic kidney disease

In-Depth [retrospective cohort]: The cohort consisted of US veterans with chronic kidney disease, defined as a glomerular filtration rate (GFR) of less than 60ml/min/1.73m² or the presence of a spot urine microalbumin-creatinine ratio of at least 30mg/g. This cohort was gathered between October 1, 2004 and September 30, 2006, and they were followed until April 30, 2012, or until death. Only patients who were available for blood pressure measurements and had a relevant increase in their blood pressure medications for their goal SBPs were included in the study to ensure that decreases in SBP could be attributed to changes in medications. To account for the inherent differences between the two blood pressure groups, propensity matching was used. This resulted in 5760 patients in both the SBP <120 mmHg group and the SBP 120-139 mmHg group. The primary outcome was all-cause mortality.

The mortality rate in the SBP <120 mmHg group was significantly higher compared to the mortality rate in the SBP 120-139mmHg group (P<0.001). In the non propensity-matched groups, the death rate in the tighter SBP group was 80.9/1000 patient-years (95% CI, 77.7-84.2/1000 patient-years), whereas the death rate for the looser SBP group was 41.8/1000 patient-years (95% CI, 41.2-42.4/1000 patient-years). The hazard ratio in the propensity score-matched cohort was 1.61 (95% CI, 1.51-1.71). This increased risk associated with tighter SBP in patients with CKD was also present in sub-group analyses, in which investigators examined patients with co-morbid conditions such as CAD, diabetes, and heart failure.

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