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

Preliminary studies have shown the potential use of salivary creatinine concentration in the diagnosis of chronic kidney disease (CKD). For saliva to replace serum as a diagnostic tool, studies must be done to determine its effectiveness in the diagnosis and staging of CKD. The aim of the present study was to evaluate the use of salivary creatinine as a safe and non-invasive alternative for identifying patients with CKD.

A cross-sectional study was conducted at Tygerberg Hospital in Cape Town, on 230 patients, across all stages of CKD. Ethical approval to conduct the study was obtained from the University of the Western Cape Biomedical Research Ethics Committee, and written informed consent was provided by each participant. Saliva and serum samples were collected for creatinine analysis and the correlation determined using Spearman's correlation. Receiver operating characteristics (ROC) analysis was used to determine the diagnostic ability of salivary creatinine. A cut-off value for optimal sensitivity and specificity of salivary creatinine to diagnose CKD with glomerular filtration rate (GFR) < 60 mL/min/1.73 m² was obtained.

Serum creatinine values ranged from 46 μmol/L to 1581 μmol/L, with a median value of 134 μmol/L. Salivary creatinine values ranged from 3 μmol/L to 400 μmol/L, with a median of 11 μmol/L. There was a strong positive correlation (r = 0.82) between serum and salivary creatinine values. 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 8.5 μmol/L yielded a sensitivity of 78.3% and specificity of 74.0% for classifying patients as having CKD based on estimated GFR < 60 mL/min/1.73 m².

The results support the potential of salivary creatinine as a non-invasive diagnostic tool for estimating GFR and identifying patients with CKD.