Sjögren’s Syndrome is a chronic autoimmune disorder where the immune system mistakenly attacks its own healthy cells, primarily those in the moisture-producing glands like the salivary and lacrimal glands. This attack leads to the common symptoms of dry eyes and dry mouth, but the disease can also affect other organs, including the lungs, kidneys, and nervous system. Diagnosis is often complex because symptoms can mimic other conditions or develop gradually over time. Blood tests play a central role in the diagnostic process, helping to identify the specific markers of this autoimmune activity and supporting the overall clinical picture.
Identifying Specific Autoantibodies
The most telling blood tests for Sjögren’s Syndrome focus on identifying highly specific autoantibodies, which are proteins produced by the immune system that target the body’s own tissues, often directed against components of the cell nucleus. The two most characteristic antibodies are Anti-Ro (also known as SSA) and Anti-La (also known as SSB). Anti-Ro is found in 60% to 80% of primary Sjögren’s patients and is a significant component of established diagnostic criteria. Anti-La is less common, appearing in about 30% to 50% of cases, and it is rarely present without Anti-Ro. The presence of both strongly suggests Sjögren’s Syndrome, though Anti-Ro alone is often sufficient. While these antibodies can appear in other autoimmune diseases like systemic lupus erythematosus, their presence is strongly indicative of the disease context and associated with a higher likelihood of systemic involvement.
Measuring General Immune Markers
General markers of autoimmune activity are measured to support a Sjögren’s diagnosis or to distinguish it from related conditions. The Antinuclear Antibody (ANA) test is often the first screen, detecting antibodies targeting the cell nucleus. A positive ANA is found in up to 80% of Sjögren’s patients, but it is also positive in many other autoimmune diseases and some healthy individuals. The Rheumatoid Factor (RF) test detects antibodies that bind to other antibodies and is present in 40% to 75% of Sjögren’s patients. While RF is traditionally associated with Rheumatoid Arthritis, its presence supports the overall picture of systemic autoimmunity, though both ANA and RF are non-specific indicators of immune system dysfunction.
Assessing Systemic Inflammation
Blood tests are used to assess the level of general systemic inflammation and to monitor for potential organ involvement. The Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) tests are non-specific measures that indicate inflammation. In Sjögren’s, the ESR is frequently elevated, often due to high levels of immune proteins in the blood, a condition called hypergammaglobulinemia. However, the CRP level is often normal even when the disease is active, meaning CRP is not a reliable marker of disease activity. A Complete Blood Count (CBC) is also routinely performed to check for complications like anemia or a low white blood cell count (leukopenia).
How Blood Tests Fit into Diagnosis
A diagnosis of Sjögren’s Syndrome requires integrating serological findings with clinical symptoms and objective non-blood tests. Results from autoantibody tests and general immune markers are combined with evidence of dryness, such as the Schirmer’s test for tear production, and sometimes a lip biopsy to examine the salivary glands. This combination of findings helps doctors meet established classification criteria, such as those set by the American College of Rheumatology and the European League Against Rheumatism (ACR/EULAR). A positive Anti-Ro (SSA) antibody test is a weighted factor in these criteria, but it must be considered alongside other clinical or pathological evidence. Importantly, a negative result for the specific autoantibodies does not completely rule out the disease; this is known as seronegative Sjögren’s Syndrome, where diagnosis relies more heavily on objective clinical tests and biopsy results.