Background The contribution of tear protein expression in patients with presumed diagnosis of Sjögren syndrome is underestimated. We aimed to evaluate the role of tear proteins in the Sjögren syndrome early diagnosis. Methods Charts from 110 patients suspected of Sjögren syndrome were analysed and the subsequent diagnosis retrieved. Subjective symptoms (ocular surface disease index, OSDI), tear film break-up time (TFBUT), Schirmer test, Jones test, tear clearance (TC), corneal (NEI score) and conjunctival staining (van Bjerstelveldt score), esthesiometry, cytology, tear protein analysis (total protein [TP] content, lysozyme-C [LYS-C], lactoferrin [LACTO], lipocalin-1 [LIPOC-1] and albumin [ALB]) were analysed. The diagnostic performance with area under the curve (AUC) and odds ratio (OR) for each parameter were calculated. Results Thirty-five patients (31.8%) had been diagnosed as affected by Sjögren syndrome. Clinical tests showed lower diagnostic performance (OSDI > 44 [AUC 0.57], Schirmer ≤ 5 mm [0.59], TFBUT ≤ 3 s [0.72], TC > 1/16 [0.68], Jones ≤ 4 mm [0.68], corneal staining > 2 [0.51], conjunctival staining > 2 [0.78]) compared with tear proteins (LYS-C ≤ 1.5 mg/mL [0.79], LACTO ≤ 20% [0.94], LIPOC-1 ≤ 10% [0.89], ALB ≥ 15% [0.79]). LYS-C, LACTO, LIPOC-1 and ALB showed a significant association in predicting Sjögren syndrome vs. not-Sjögren syndrome dry eye (OR, respectively, 4.9, 5.5, 7.2, 6.7). Conclusions Tear proteins' concentrations showed a significant higher accuracy compared with the traditional ocular clinical tests for reaching Sjögren syndrome's diagnosis. In particular, LACTO and LIPOC-1 provided an excellent diagnostic performance and thus could likely be considered promising biomarkers of Sjögren syndrome.
Keywords: Dry eye; Sjögren syndrome; proteomics; tear proteins.