Hello Aliya !

I found this about diagnosis at wikipedia (perhaps you have already read it... )

Here it is in case you (or anyone else) havent.

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Diagnosis

Diagnosing Sjögren’s syndrome is complicated by the range of symptoms a patient may manifest, and the similarity between symptoms from Sjögren's syndrome and those caused by other conditions. Nevertheless, the combination of several tests can lead to a diagnosis of Sjögren's syndrome.

Blood tests can be done to determine if a patient has high levels of antibodies that are indicative of the condition, such as anti-nuclear antibody (ANA) and rheumatoid factor (because SS frequently occurs secondary to rheumatoid arthritis), which are associated with autoimmune diseases. Typical Sjögren's syndrome ANA patterns are SSA/Ro and SSB/La, of which SSB/La is far more specific; SSA/Ro is associated with numerous other autoimmune conditions but are often present in Sjögren's.[4]

The Schirmer test measures the production of tears: a strip of filter paper is held inside the lower eyelid for five minutes, and its wetness is then measured with a ruler. Producing less than five millimeters of liquid is usually indicative of Sjögren's syndrome. However, lacrimal function declines with age or may be impaired from other medical conditions. A slit-lamp examination is done to look for dryness on the surface of the eye. Salivary gland function can be tested by collecting saliva and determining the amount produced in a five minute period. A lip biopsy can reveal lymphocytes clustered around salivary glands, and damage to these glands due to inflammation.

A radiological procedure can also be used as a reliable and accurate way of diagnosing Sjögren's syndrome. A contrast agent is injected into the parotid duct (of Stensen), which is a duct opening from the cheek into the vestibule of the mouth opposite the neck of the upper second molar tooth. Widespread puddling of the injected contrast scattered throughout the gland indicates Sjögren's syndrome.
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Also, there is lots of info in the Sjögren's Syndrome Foundation website here

Hope that helps and good luck !