To assess the sensitivity and specificity of the lactoferrin tear test (LTT) in the diagnosis of keratoconjunctivitis sicca due to Sjögren's syndrome (SS), comparing it with the other lacrimal tests and with immunological tests.
25 patients suffering from SS (24 women and 1 man, median age 51.5 years, s.d. 16.3); control group: 20 patients with various kinds of conjunctivitis without dry eye. Tests in both groups: Schirmer I (ST), BUT, ferning test, lactoferrin immunoassay, fluorescein and Rose Bengal staining. Immunological tests: serum titers of anti-nuclear (ANA), anti-DNA, anti-ENA (SS-A, SS-B, RNP, FR) antibodies. In the patients with SS, labial salivary gland biopsy was also performed.
LTT had a specificity of 95% and a sensitivity of 72%, compared to 85% and 64% for the Schirmer I test. The ferning test has the highest sensitivity (92%), and none of the cases positive to BUT was negative to the ferning test. The combination of LTT and ferning test gave a value of 78% compared to 70% with ST. The correlations between positive LTT and positive ANA, SS-A and labial biopsy were respectively 83%, 67% and 80%, as against 67%, 50% and 65% for the Schirmer I test.
In our study, LTT showed very high specificity, good sensitivity particularly when combined with qualitative tear tests, and a good correlation with the immunological and bioptic tests for SS. Since it is easy to perform, in our opinion LTT can be included in the diagnostic routine for keratoconjunctivitis sicca in SS.