MRCP2-4783

A 54-year-old woman comes to the clinic complaining of fatigue and dry eyes that have been bothering her for a few months. She also reports having a significantly dry mouth, which sometimes makes it difficult for her to eat. She has no notable medical history.

During the examination, the doctor observes mild redness in the eyes and a dry tongue. Suspecting a particular diagnosis, the doctor orders an initial blood test:

Antinuclear antibodies 1:1600 (<1:280) What is the most conclusive test to confirm the suspected diagnosis?