Association of low blood pressure with increased mortality in patients with moderate to severe chronic kidney disease

Background. Blood pressure shows an inverse association with mortality in patients with chronic kidney disease (CKD) on dialysis. It is unclear if the same phenomenon exists in patients with CKD not yet on dialysis. Methods. We examined the association of systolic (SBP) and diastolic (DBP) blood pressure with all-cause mortality in a historical prospective cohort of 860 patients (age 68.1 +/- 10.1 years, 99.1% male, 24.4% black) with estimated glomerular filtration rate (GFR) < 60 ml/min/1.73 m(2). We used Cox models to adjust for the effects of age, race, diabetes mellitus, atherosclerotic cardiovascular disease (ASCVD), congestive heart failure, smoking, antihypertensive medications, body mass index, GFR, albumin, cholesterol, haemoglobin and proteinuria. To examine the role of comorbidities, we performed subgroup analyses based on prevalent ASCVD status and level of estimated GFR. Results. Higher SBP and higher DBP were both associated with lower mortality [adjusted hazard ratio (95% confidence interval) for SBP 133-154, 155-170 and > 170 mmHg, compared with < 133 mmHg, respectively: 0.61 (0.44-0.85), 0.62 (0.45-0.87) and 0.68 (0.49-0.96); and for DBP 65-75, 76-86 and > 86 mmHg, compared with < 65 mmHg: 0.85 (0.62-1.18), 0.72 (0.52-1.00) and 0.60 (0.41-0.86)]. The same association was present for both SBP and DBP only in subgroups with GFR <= 30 ml/min/1.73 m(2) and for DBP only in the subgroup with ASCVD. Conclusions. Lower blood pressure is associated with higher mortality in patients with moderate to severe CKD, but interactions with kidney function and with ASCVD suggest that blood pressure may play a surrogate rather than a causative role in this association.