Sjögren’s Syndrome is a long-term autoimmune disease where the immune system mistakenly attacks moisture-producing glands, primarily the lacrimal glands (tears) and salivary glands (saliva). This attack causes chronic inflammation and progressive damage, leading to the characteristic symptoms of severe dry eyes and dry mouth. Because the symptoms can mimic other conditions, diagnosis requires combining a patient’s clinical presentation with specific laboratory tests. Blood work plays a central role by looking for signs of the errant immune activity associated with the disease.
Searching for Primary Autoantibodies
The most direct blood test for Sjögren’s Syndrome involves looking for highly specific proteins called autoantibodies. These immune system proteins are incorrectly directed against the body’s own tissues, which is the hallmark of an autoimmune condition. The two primary autoantibodies tested for are anti-Ro (SS-A) and anti-La (SS-B).
These antibodies are considered the strongest blood indicators and are included in the official diagnostic classification criteria. Anti-Ro (SS-A) antibodies are found in approximately 70% or more of Sjögren’s patients, making them the most sensitive serological marker. The presence of anti-Ro antibodies is associated with greater disease severity and longer duration.
Anti-La (SS-B) antibodies are less common, present in approximately 40% of patients, and are rarely found without anti-Ro antibodies also being present. Although less frequent, a positive anti-La result is considered highly specific to Sjögren’s Syndrome. The detection of either or both of these specific autoantibodies provides powerful evidence supporting a diagnosis, particularly in patients with corresponding dry eye and dry mouth symptoms.
Supporting Blood Markers for Diagnosis
Beyond the specific anti-Ro and anti-La autoantibodies, several other blood markers are routinely checked to look for general signs of systemic inflammation and autoimmune activity. These supporting tests are important because they can indicate that the immune system is generally overactive, even if the primary autoantibodies are not present. One such screening test is the Antinuclear Antibody (ANA) test, which is positive in the majority of Sjögren’s patients.
The ANA test detects antibodies that target components within the nucleus of a cell, but it is not specific to Sjögren’s and is found in many autoimmune diseases. Another common finding is a positive Rheumatoid Factor (RF), an antibody often associated with Rheumatoid Arthritis but present in up to 70% of Sjögren’s patients. The RF test signals general immune dysregulation by indicating the presence of immunoglobulins binding to other immunoglobulins.
Markers of general inflammation, such as the Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP), are also part of the standard blood panel. An elevated ESR or CRP suggests inflammation somewhere in the body, aligning with the systemic nature of Sjögren’s Syndrome. While these non-specific markers cannot confirm the disease alone, their presence helps paint a broader picture of an ongoing autoimmune process.
Beyond Blood Tests
No single blood test is sufficient to confirm a diagnosis of Sjögren’s Syndrome. Doctors rely on objective evidence of damage to the moisture-producing glands to complete the diagnostic picture. These evaluations focus on measuring the actual function of the eyes and salivary glands to determine the extent of the dryness.
One common procedure is the Schirmer’s test, which measures tear production by placing small strips of filter paper under the lower eyelids. Objective tests also measure the flow rate of saliva, known as sialometry, to assess salivary gland function. These function tests provide direct evidence of glandular hypofunction, which is the physical manifestation of the disease.
The most definitive non-blood test is often the minor salivary gland biopsy, typically performed on the inner lip. This procedure involves removing a small tissue sample containing tiny salivary glands for microscopic examination. The biopsy looks for characteristic clusters of inflammatory cells, specifically lymphocytes, which infiltrate and damage the glands.
Understanding Your Test Results
A positive blood test for anti-Ro or anti-La antibodies is a strong indicator, but it does not automatically guarantee a diagnosis. Conversely, a negative result does not necessarily mean the disease is absent, a situation known as seronegative Sjögren’s Syndrome. Up to 30% of diagnosed patients may test negative for the anti-Ro antibody.
False negatives can occur, particularly in patients with a milder or earlier form of the disease or those whose symptoms are primarily neurological. This highlights why the clinical picture, including symptoms and objective dryness tests, must be considered alongside serology. False positives can also occur, as anti-Ro antibodies are sometimes found in other autoimmune diseases like lupus or in a small percentage of healthy individuals.
Ultimately, diagnosing Sjögren’s Syndrome requires a rheumatologist to interpret all information together: the patient’s symptoms, the results of specific and supporting blood tests, and objective evidence of glandular damage. The blood work serves as a crucial piece of evidence, but comprehensive clinical correlation leads to a definitive diagnosis.