Efficacy of Salivary Urea and Creatinine Compared to Serum Levels in Chronic Kidney Disease Patients: A Cross-sectional Study

Abstract

Introduction: Chronic Kidney Disease (CKD) has become an impending health concern due to the massive rise in the number of patients with diabetes mellitus and hypertension. Monitoring CKD patients typically requires regular invasive testing, and a simple diagnostic test that does not involve venipuncture would greatly benefit patients and healthcare professionals. Extensive research is being conducted to explore the use of saliva as a Non invasive tool for evaluation of systemic diseases like CKD. However, most of these studies have focused on End Stage Renal Disease (ESRD) patients. Aim: To investigate the correlation between salivary urea and creatinine levels and their serum counterparts in CKD patients and healthy controls. Additionally, the study aimed to assess the efficacy of salivary urea and creatinine compared to serum urea and creatinine in predicting CKD. Materials and Methods: The present cross-sectional study was conducted between January 2021 and July 2022 in the Department of Biochemistry, in collaboration with the Department of Medicine, at Heritage Institute of Medical Sciences in Varanasi, Uttar Pradesh, India. The study included a total of 60 participants: 30 CKD patients (stage 1-3) and 30 age-matched healthy controls. Serum and salivary urea were analysed using the Urease-Glutamate Dehydrogenase (GLDH) method, and creatinine was measured using the Modified Jaffe’s method on the Dirui-300B autoanalyser. Data were statistically analysed using Pearson’s correlation coefficient. The sensitivity, specificity, and Area Under the Curve (AUC) of salivary urea and creatinine were evaluated in comparison to their serum counterparts. Results: The participants consisted of 30 CKD patients with a mean age of 54.8±8.8 years and 30 age-matched healthy controls with a mean age of 52.42±8.4 years. A significant difference in salivary urea and creatinine levels was observed between the control and CKD groups. There was a strong and significant correlation (p-value <0.01) between salivary creatinine and serum creatinine in both the control group (r-value=0.76) and the CKD group (r-value=0.82). Additionally, a strong and significant correlation (p-value <0.01) was found between salivary urea and serum urea in the CKD group (r-value=0.63). However, the correlation between salivary and serum urea was not significant in the control group, with an r-value of 0.58 and a p-value of 0.24. Both salivary urea and creatinine demonstrated high sensitivity (90% and 89%, respectively), specificity (80% and 80%, respectively), and AUC (0.78 and 0.86, respectively) compared to their serum counterparts, validating their practical clinical utility. Conclusion: The concentration of urea and creatinine in saliva can reflect kidney damage and help monitor kidney function in CKD patients. Standardising the protocol for evaluation of salivary urea and creatinine and establishing a reference range will make it useful for screening for CKD.