Electroconductivity of Saliva as a Diagnostic Tool for Dry Eye Disease: A Case-Control Study

To evaluate the diagnostic potential of body fluid electroconductivity for dry eye disease (DED) and compare its accuracy with commonly used DED tests. Individuals with dry eye (n = 36) and controls (n = 26) were enrolled in this case-control prospective study. Electroconductivity measurements were performed on blood, serum, tears, urine, and saliva. Dry eye assessments included tear film breakup time (TBUT) and Schirmer test (Schirmer), with symptoms evaluated using the Ocular Surface Disease Index (OSDI). Blood and urine analyses were performed to assess the baseline systemic profiles of both groups. Among all body fluids, saliva (saliva electroconductivity [ESaliva]) showed the most significant differences in electroconductivity between controls and dry eye individuals (2514.02 ± 329.18 vs. 3262.00 ± 992.47 µS/cm, P < 0.001). ESaliva showed robust diagnostic performance (area under the curve [AUC] = 0.800), comparable to TBUT (AUC = 0.693, P = 0.103) and superior to Schirmer (AUC = 0.536, P < 0.001). OSDI showed a moderate correlation with ESaliva (r = 0.43, P < 0.001), representing the strongest association, followed by TBUT (r = -0.26, P = 0.004) and Schirmer (r = -0.09, P = 0.313). Cross-validation procedure identified ESaliva cutoffs of 2373 µS/cm (95% confidence interval [CI], 2340-2456) for low-to-moderate and 2880 µS/cm (95% CI, 2845-2931) for moderate-to-high DED risk. Net reclassification improvement and integrated discrimination improvement analyses confirmed ESaliva's superior predictive ability. A single cutoff of 2880 µS/cm yielded 64% sensitivity and 89% specificity for DED prediction. ESaliva effectively distinguishes patients with DED and exhibits superior diagnostic performance. ESaliva: offers a noninvasive and self-assessable tool for DED diagnosis.