Cut-off levels of salivary beta2-microglobulin and sodium differentiating patients with Sjögren's syndrome from those without it and healthy controls

For the diagnosis of Sjögren's syndrome (SS), cut-off levels of β2-microglobulin (β2MG) and sodium (Na+) in unstimulated whole saliva have not yet been shown. We aimed to determine the cut-off levels of salivary β2MG and Na+ which differentiate SS patients from non-SS patients and healthy controls. Seventy-one patients of primary SS (pSS, 69 females/2 males, 60.0±16.8 years old), 50 of secondary SS (sSS, 49/1, 55.8±17.4), 54 of connective tissue diseases other than SS (non-SS-CTD, 43/11, 60.0±16.0), and 75 healthy volunteers (HC, 43/32, 50.7±15.6) were included. Unstimulated whole saliva were examined for levels of β2MG, Na+, potassium (K+), and chloride (Cl-). Receiver-operating characteristic curve analysis was carried out. β2MG, Na+, and Cl- levels in the SS group (pSS and sSS) were significantly higher than those in the non-SS group (non-SS-CTD and HC). The salivary β2MG level was 5.3±4.6 mg/L in pSS, 5.1±2.0 in sSS, 2.5±2.1 in non-SS-CTD, and 1.2±0.7 in HC, respectively. The Na+ level was 39.2±25.2 mEq/L, 36.4±26.1, 19.6±16.8, and 16.5±7.3, and the Cl- level was 51.1±25.0, 47.8±24.3, 32.1±16.6, and 27.0±7.9 in the same order. The K+ level in the SS group was significantly higher than that in HC. The optimal cut-off β2 MG and Na+ levels that differentiate the SS group from the non-SS group were 2.3 mg/L and 23 mEq/L. Salivary β2MG and Na+ levels are useful markers for differentiating SS patients from non-SS-CTD patients and HC.