Salivary creatinine as a diagnostic tool for evaluating patients with chronic kidney disease

Abstract

BACKGROUND Preliminary studies have shown the potential use of saliva in the diagnosis of chronic kidney disease (CKD). For saliva to completely replace serum as a diagnostic and monitoring tool for CKD, studies must be done to determine its effectiveness as a substitute in diagnosing chronic kidney disease, at each stage of the disease. Aim: The aim of the study was to evaluate the role of saliva as a safe and non-invasive alternative to serum, for creatinine estimation, in all stages of chronic kidney disease. METHOD A cross sectional study was conducted at the Renal Unit of Tygerberg Hospital, on 230 patients at all stages of CKD. Informed consent was obtained; thereafter saliva and serum samples were collected for creatinine analysis. Correlation between serum and salivary creatinine was determined using Spearman's correlation test. Receiver Operating Characteristics (ROC) analysis was used to determine the diagnostic ability of salivary creatinine and a cut-off value for sensitivity and specificity of salivary creatinine to diagnose CKD with GFR < 60ml/min was obtained. RESULTS Serum creatinine values ranged from 46?mol/L to 1581?mol/L with a median value of 134?mol/L. Salivary creatinine values ranged from 3?mol/L to 400?mol/L with a median of 11?mol/L. Spearman's correlation analysis showed a strong positive correlation (r = 0.82) between serum and salivary creatinine values for all CKD stages. Linear regression analysis of serum and salivary creatinine for CKD patients was significant in all CKD stages, except for stage 1. Area under the curve for salivary creatinine was 0.839. A cut-off value of 8.50?mol/L showed a sensitivity of 78.3% and specificity of 74.0% at eGFR < 60ml/min, for classifying patients as having CKD.