Background: This study compares the associations of predialysis systolic blood pressure (SBP) with mortality risk in both incident and prevalent hemodialysis (HD) cohorts by using both conventional and time-varying Cox analyses, thus addressing limitations of prior studies.
Methods: A total of 56,338 incident patients starting HD therapy during 1997 to 2001 and 69,590 prevalent HD patients on January 1, 2002, were grouped into the following categories: (1) SBP less than 120 mm Hg, (2) 120 < or = SBP < 140 mm Hg, (3) 140 < or = SBP < 160 mm Hg, (4) 160 < or = SBP < 180 mm Hg, (5) 180 < or = SBP < 200 mm Hg, and (6) SBP of 200 mm Hg or greater. Conventional and time-varying models evaluated 1-year and 3-year (incident patients only) survival.
Results: Nine percent and 26.0% of incident patients and 5.7% and 20.1% of prevalent patients were in categories 1 and 2, respectively. Their associated 1-year hazard ratios (HRs) were 2.63 to 3.68 and 1.57 to 1.68 compared with category 4, the reference group. HRs for categories 3, 5, and 6 were not different from category 4. Time-varying models magnified category 1 and 2 HRs to 5.54 to 7.42 and 1.92 to 2.21, such that 25% to 35% of patients in the target SBP range (< 140 mm Hg) had the greatest risk. A "reversed J-shaped" risk profile emerged in the time-varying models, with very high SBP (category 6) associated with HRs of 1.52 to 1.55, but only 1% of patients were in category 6. Three-year outcomes were similar.
Conclusion: Epidemiological characteristics of predialysis SBP consistently differ from those in the general population despite different analytic perspectives. The data suggest a need for greater investigative, diagnostic, and therapeutic focus on HD patients with normal and prehypertensive blood pressure ranges.