Kidney function and systolic blood pressure new insights from cystatin C: Data from the Heart and Soul Study

Background: Control of hypertension is paramount in treating chronic kidney disease. The relationship between kidney function and blood pressure (BP) components has been studied in persons with diagnosed CKD, diabetes, or hypertension. Whether kidney function in the normal range is associated with systolic BP (SBP), diastolic BP (DBP), and pulse pressure is unclear. Methods: We evaluated the association between kidney function and each BP component using cystatin C and 24-h creatinine clearance (CrCl) among 906 participants in the Heart and Soul Study. Results: We observed that SBP was linearly associated with cystatin C concentrations (1.19 +/- 0.55 mm Hg increase per 0.4 mg/L cystatin C, P = .03) across the range of kidney functions. In contrast, using CrCl, SBP was significantly associated with kidney function only in subjects with CrCl < 60 mL/min (6.4 +/- 2.13 mm Hg increase per 28 mL/min, P = .003) but not > 60 mL/min (0.36 +/- 0.77 mm Hg per 28 mL/min, P = .64). Slopes differed significantly (for spline term P = .001). We found that DBP was not associated with cystatin C (0.34 +/- 0.40 mm Hg per 0.4 mg/L cystatin, P = .39) or CrCl (0.62 +/- 0.44 mm Hg per 28 mL/min clearance, P = .16). Pulse pressure was linearly associated with cystatin C (1.28 +/- 0.55 mm Hg per 0.4 mg/L cystatin, P = .02) and with CrCl < 60 mL/min (7.27 +/- 2.16 mm Hg per 28 mL/min, P = .001). Conclusions: Both SBP and pulse pressure were significantly associated with kidney function across a wide range of cystatin C concentrations, even in subjects with presumably normal kidney function, by creatinine-based measures. Cystatin C may provide new insights into the association of CKD and hypertension, a relationship that may be an underappreciated barrier to hypertension control.