Sjögren’s syndrome is a chronic autoimmune disease where the immune system mistakenly attacks the body’s own moisture-producing glands, primarily those responsible for tears and saliva. This leads to common symptoms like dry eyes and dry mouth. The disease can occur alone or alongside other autoimmune conditions such as rheumatoid arthritis or lupus, and it can also affect other organs like the lungs, kidneys, and nervous system. Diagnosis is complex, often requiring a combination of factors, with blood tests serving as a significant component.
Key Blood Markers for Sjögren’s Syndrome
Diagnosing Sjögren’s syndrome frequently involves identifying specific autoantibodies in the blood, which are proteins produced by the immune system that mistakenly target the body’s own tissues. Two prominent autoantibodies are Sjogren’s syndrome A (SS-A/Ro) and Sjogren’s syndrome B (SS-B/La). SS-A/Ro antibodies are found in 60% to 80% of Sjögren’s patients, while SS-B/La antibodies are less common, appearing in 30% to 50% of cases. The presence of both SS-A and SS-B antibodies can strengthen a Sjögren’s diagnosis.
SS-A/Ro and SS-B/La are extractable nuclear antigens. Antibodies against these proteins indicate an autoimmune response often seen in Sjögren’s syndrome. While SS-A/Ro and SS-B/La antibodies are strongly associated with Sjögren’s, they can also be present in other autoimmune conditions like systemic lupus erythematosus (SLE).
Antinuclear Antibodies (ANA) are another type of autoantibody often tested in suspected autoimmune diseases, including Sjögren’s syndrome. A positive ANA test indicates autoantibodies targeting components within the cell’s nucleus. While a majority of Sjögren’s patients test positive for ANA, it is not specific to the disease and can be found in healthy individuals or those with other autoimmune disorders. ANA results are typically reported as a titer, such as 1:80 or 1:160, with higher titers generally suggesting a greater likelihood of autoimmune disease.
Other Blood Tests for Sjögren’s Diagnosis
Beyond specific autoantibodies, other blood tests provide supporting evidence or help differentiate Sjögren’s syndrome from other conditions. Rheumatoid Factor (RF) is an autoantibody typically associated with rheumatoid arthritis, but it is also frequently detected in Sjögren’s patients, appearing in 60% to 70% of cases. Its presence in Sjögren’s does not necessarily indicate co-occurring rheumatoid arthritis. An RF test may also be positive in various other conditions, including certain infections.
Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) are general markers of inflammation in the body. An elevated ESR or CRP suggests systemic inflammation, which can be present in Sjögren’s syndrome. While these markers indicate active inflammation, their levels in Sjögren’s are often less pronounced compared to other inflammatory conditions like rheumatoid arthritis.
Immunoglobulin levels, specifically IgG, IgA, and IgM, are also assessed. Patients with Sjögren’s syndrome may exhibit elevated levels of these immunoglobulins, a condition known as hypergammaglobulinemia. Elevated IgG levels, in particular, can be associated with a greater number of extra-glandular manifestations and increased organ damage in primary Sjögren’s syndrome.
A Complete Blood Count (CBC) and a Complete Metabolic Panel are routinely performed to assess overall health and identify any related abnormalities. The CBC evaluates red blood cells, white blood cells, and platelets. A low white blood cell count (leukopenia) may be found in 15% to 20% of Sjögren’s patients, though it generally does not increase infection risk. The metabolic panel measures electrolytes and other substances reflecting kidney and liver function; for instance, elevated liver enzymes can be seen in some liver diseases more common in Sjögren’s.
The Complete Diagnostic Picture
Blood tests alone are often insufficient for a definitive diagnosis of Sjögren’s syndrome, as the clinical presentation can mimic other conditions and symptoms may develop gradually. A thorough diagnostic process integrates blood test results with a comprehensive evaluation of clinical symptoms, such as persistent dry eyes and mouth. Patients commonly report a gritty sensation in their eyes or difficulty swallowing dry foods.
Objective tests for dryness are also performed to assess glandular function. The Schirmer’s test measures tear production by placing a small strip of filter paper under the lower eyelid for five minutes; a wetting of less than 5 or 10 mm/5 min is indicative of aqueous tear deficiency. Salivary flow rate can be measured to assess oral dryness, with an unstimulated whole salivary flow rate of less than 0.1 mL/min often considered a significant finding.
A biopsy of minor salivary glands, typically taken from the inner lower lip, is a significant diagnostic procedure. It involves removing a small tissue sample to examine it under a microscope for characteristic lymphocytic infiltration, which are clusters of inflammatory cells. A focus score of one or more lymphocyte clusters per 4 mm² of glandular tissue is a common finding indicative of Sjögren’s.
Imaging studies can also provide supportive information regarding salivary gland function and structure. Sialography, a special X-ray that involves injecting dye into the salivary glands, can show how saliva flows. Salivary scintigraphy, a nuclear medicine test, tracks a radioactive isotope to assess how quickly it reaches the salivary glands. Newer techniques like ultrasonography and magnetic resonance imaging (MRI) of salivary glands are also employed, offering insights into structural changes and inflammation.
It is important to understand the concept of “seronegative Sjögren’s,” where patients meet clinical criteria and other objective findings but do not have the typical SS-A/Ro and SS-B/La antibodies. Approximately 20% to 40% of Sjögren’s patients may lack these antibodies. In such cases, a positive minor salivary gland biopsy becomes particularly important for confirming the diagnosis. A negative blood test for these antibodies does not rule out the disease if symptoms and other diagnostic findings are present.