Hypervolemia and blood pressure in prevalent kidney transplant recipients

BACKGROUND: The prevalence and consequences of hypervolemia in kidney transplant recipients (KTRs) have not been investigated. Specifically, its impact on blood pressure (BP) and relationship with N-terminal fragment of prohormone B-type natriuretic peptide (NT-proBNP) are unknown. The objectives of this study were to establish the prevalence of hypervolemia among clinically stable KTRs, investigate the predictors of posttransplant hypervolemia, assess its impact on blood pressure, and determine its relationship with NT-proBNP.

METHODS: This single-center cross-sectional study enrolled 123 clinically stable KTRs. Extracellular volume status was determined by multifrequency bioimpedance analysis. Mild and severe hypervolemia were defined as percentage volume expansion of greater than 7% and greater than 15%, respectively. Systolic BP (SBP) and diastolic BP (DBP) were measured, with mean arterial pressure (MAP) calculated. Serum NT-proBNP was quantified using a noncompetitive immunoluminometric assay. Potential demographic, nutritional, and clinical predictors of extracellular volume status, BP, and NT-proBNP levels were assessed.

RESULTS: Hypervolemia was present in 30% of KTRs, with 5% classified as severe hypervolemia. Significant predictors of volume expansion were increased sodium intake, advancing age, and reduced fat mass (P<0.01 for all associations). Hypervolemia was the only independent predictor of elevated MAP, SBP, and DBP (P<0.001 for all associations). Raised NT-proBNP levels were independently associated with both hypervolemia (P=0.01) and allograft dysfunction (P=0.03).

CONCLUSIONS: Hypervolemia is unexpectedly common among clinically stable KTRs. It is closely associated with elevated BP. The relationship with increased sodium intake signals potential therapeutic focus. Further study is warranted to prospectively investigate objective measures of extracellular volume status among KTRs.