Beta 2 microglobulin measurements in saliva of patients with primary Sjögren's syndrome: influence of flow.

OBJECTIVES To determine the diagnostic value of beta 2 microglobulin in parotid saliva, its concentration in relation to salivary flow was determined in 29 patients with primary Sjögren's syndrome and in 30 normal controls. The specific secretion rate of beta 2 microglobulin was calculated. METHODS Parotid saliva samples were collected within a 20 minute period directly from Stensen's duct with Lashley cups: sample 1 without gustatory stimulation during the first 10 minutes and samples 2 and 3 during the next five to 10 minutes, when saliva production was stimulated by a 500 mg vitamin C tablet. The sample volumes were measured and the beta 2 microglobulin concentration was determined by radioimmunoassay. RESULTS During gustatory stimulation the mean beta 2 microglobulin secretion rate in patients with primary Sjögren's syndrome was 0.31 microgram/min; in normal controls it was 0.14 microgram/min. The sensitivity and specificity of this test were 56 and 87% respectively. The mean salivary flow without stimulation in patients with primary Sjögren's syndrome was lower than that in normal controls, but no difference was found during stimulation. CONCLUSIONS Our results support the hypothesis of local beta 2 microglobulin production in the parotid gland of patients with primary Sjögren's syndrome. The test cannot be used as a screening test owing to low sensitivity, but it may be used as a supplementary diagnostic test as it has the advantage of being non-invasive.