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Longitudinal Relationships among Coronary Artery Calcification, Serum Phosphorus, and Kidney Function

Katherine R. Tuttle^*,, and Robert A. Short^*,

^* Providence Medical Research Center at Sacred Heart Medical Center, Spokane, Washington; Nephrology Division, Department of Medicine, University of Washington School of Medicine, Seattle, Washington; and Spokane Heart Study, Office of Research, Washington State University, Spokane, Washington

Correspondence: Dr. Katherine R. Tuttle, Providence Medical Research Center, 104 W. 5th Avenue, Suite 350E, Spokane, WA 99224. Phone: 509-474-4345; Fax: 509-474-4325; E-mail: katherine.tuttle{at}providence.org

Background and objectives: Coronary artery calcification (CAC) is common in advanced chronic kidney disease (CKD), yet its onset and time course are uncertain. The study objective was to assess longitudinal relationships among CAC, kidney function, and traditional and putative cardiovascular disease (CVD) risk factors.

Design, setting, participants, & measurements: This is a prospective cohort analysis from the Spokane Heart Study, a long-term observational study of community-dwelling adults who were assessed every 2 yr for CAC (electron-beam computed tomography), CVD risk factors, and laboratory testing. Estimated GFR (eGFR) was determined by the reexpressed Modification of Diet in Renal Disease equation.

Results: CAC was present in 28% (245 of 883) at baseline. After 6 yr, new-onset CAC developed in 33% (122 of 371); severity increased from a median CAC score of 38 to 152 in those with baseline CAC. Neither eGFR (101 ± 34 versus 104 ± 31 ml/min per 1.73 m², respectively) nor serum phosphorus (3.25 ± 0.49 versus 3.29 ± 0.48 mg/dl, respectively) differed by CAC presence or absence at baseline; however, multivariate models (generalized estimating equations for incidence and prevalence) revealed that independent predictors of CAC over time were greater baseline CAC scores, higher serum phosphorus levels, lower eGFR levels, and traditional CVD risk factors. Each 1-mg/dl increase in phosphorus imparted odds ratios for CAC of 1.61 (incidence) and 1.54 (prevalence), risks comparable to traditional CVD risk factors.

Conclusions: CAC becomes more frequent and severe over time. Higher levels of serum phosphorus and reduced kidney function independently predicted CAC.