Sonographic renal cortical signs predicting renal function among chronic kidney desease patients at Muhimbili national hospital

Abstract

Objective: To determine whether renal sonography pathological changes can be used to predict renal function among patients with chronic kidney disease (CKD). Methods: This was a cross-sectional study which evaluated 145 patients with CKD who underwent both kidney sonography and renal function test based on estimated glomerular filtration rate (eGFR) by MORO equation. These patients were recruited from Diabetic, Hypertensive and Nephrology clinics at Muhimbili National Hospital from June to December 2009. A systematic random sampling was used based on the fore mentioned clusters (Diabetic, Hypertensive and Nephrology clinics). Hricak standardized measure of renal cortical echogenicity scoring was used as Grade 0; Grade I; Grade II and Grade Ill. Cortical volume was also calculated and obtained as a renal volume minus central echogenic complex (sinus) volume. These three variables were analyzed looking for correlation, sensitivity, specificity, positive and negative predictive values and Likelihood Ratio. Renal function test using eGFR by MDRD equation was used as the gold standard. Results: The regression correlation between renal cortical echogenicity and renal function (eGFR) revealed a correlation coefficient of r2 = 0.622, p<O.OO I. The sensitivity of echogenicity as predictor of renal function was 74.7% (95% CT: 0.68 - 0.78), specificity was 93.5% (95% Cl: 0.85 - 0.99). Positive Likelihood Ratio (LR) +11.6; p<O.OOI), hence echogenicity proved to be a strong prediction sign. To be more precise, it was shown that cortical echogenicity grade I or below shows renal function of more than 60 mLlminll.73 m2 and echogenicity grade II or more presents with a compromised renal function below 59 mLlminll.73 m2 Right and left renal cortical volume as relates to estimated GFR showed correlation coefficient of r ;::;; +0.49 and r= +0.43 respectively. It revealed within +0.7 and +0.3 range which defines a weak linear association. It showed the regression slope b with (95%CI: 0.50-1.04) and correlation coefficient ofr2=0.184; p<O.OOI.

VII Conclusions: The observed correlations between renal cortical echogenicity, renal cortical parenchyma volume change and renal function estimated by GFR suggest that: 1. Renal cortical echogenicity sign may potentially be useful as surrogate marker of the renal function. 2. Renal cortical volume as a predictor of renal function did not qualify our alternative hypothesis. 3. At present however, precise prediction of renal function based on a renal cortical volume change requires a big sample size for the specific conclusion since its significance testing shows a confidence interval with high prediction variability.