Applicability of Saliva for Evaluation of Some Biochemical Parameters of Kidney and Liver Function in Healthy Individuals

Proper diagnosis of clinical conditions is a major goal of clinical and biochemical analyses. Recently, increasing efforts have been put on the use of less invasive sampling techniques with optimal sensitivity and specificity. The aim of this study was to investigate the applicability of saliva instead of blood for measuring biochemical parameters of liver and kidney function in healthy individuals.     

Plasma and saliva samples were collected from 100 healthy volunteers to measure level of alkaline phosphatase (ALP), alanine transaminase (ALT), aspartate aminotransferase (AST), total bilirubin, gamma-glutamyl transpeptidase (GGT), urea and creatinine using a fully automated chemistry analyzer (ACE Alera) with ready to use validated kits. Receiver operating characteristic (ROC) analysis was carried out using MediCal program to calculate sensitivity and specificity and area under ROC (AUC).     

The mean (standard deviation) salivary level of ALP, AST, ALT, GGT, total bilirubin, creatinine and urea was 20.9 (20.7) U/L, 25.8 (17.9) U/L, 10.6 (11.8) U/L, 9.6 (4.37) U/L, 0.16 (0.13) mg/dL, 0.09 (0.05) mg/dL and 35.6 (15.2) mg/dL, respectively. Saliva to blood ratios of ALP, AST, ALT, GGT, total bilirubin, creatinine and urea was 14%, 113%, 65%, 45%, 19%, 12% and 130%, respectively. The suggested normal saliva ranges of ALP, AST, ALT, GGT, total bilirubin, creatinine and urea were 7-98 (U/L), 31-104 (U/L), 6-31 (U/L), 15-24 (U/L), 0-0.13 (mg/ dL), 0.14-0.31 (mg/ dL) and 45-74 (mg/ dL), respectively.  The calculated sensitivity and specificity values were 38%  and 85% for ALP), 80% and 76% for AST, 75% and 45% for ALT, 60%  91% for GGT, 49% and 38% for total bilirubin, 20% and 91% for creatinine and 100% and 75% for urea. The AUC was higher than 0.7 for urea, GGT and AST, indicating good sensitivity and specificity of saliva testing for evaluation of these enzymes.  

Based on the results, saliva could be as a noninvasive method of assessing kidney and liver function. Saliva may be a favorable alternative to plasma for measuring level of urea, GGT and AST in humans.