Systemic Lupus Erythematosus (SLE) is a chronic autoimmune condition where the body’s immune system mistakenly attacks its own healthy tissues, leading to widespread inflammation and tissue damage across multiple organ systems. SLE can affect the skin, joints, kidneys, brain, and blood cells, making its presentation highly variable among individuals. To bring uniformity to research and clinical trials, the American College of Rheumatology (ACR) developed a set of 11 classification criteria in 1982, revised in 1997. These criteria are intended to identify a specific, homogeneous group of patients for study, rather than serving as the sole method for clinical diagnosis.
Listing and Explaining the Eleven Criteria
The 11 ACR criteria are divided into clinical and laboratory findings.
- Malar Rash: Fixed redness across the cheeks and bridge of the nose, often described as a butterfly pattern, which characteristically spares the nasolabial folds.
- Discoid Rash: Raised, red patches with adherent scaling that can lead to scarring and changes in skin pigmentation over time.
- Photosensitivity: A skin reaction resulting from an unusual sensitivity to sunlight, which can be reported by the patient or observed directly by a physician.
- Oral or Nasopharyngeal Ulcers: Sores in the mouth or nose, which are often painless and must be observed by a healthcare provider.
- Arthritis: Non-erosive inflammation in two or more peripheral joints, identified by swelling, tenderness, or effusion. This joint involvement typically causes pain and swelling but does not permanently destroy the bone structure.
- Serositis: Inflammation of the lining around the lungs (pleuritis) or the heart (pericarditis). Pleuritis is identified by pain with breathing, while pericarditis is confirmed by an electrocardiogram or evidence of fluid accumulation around the heart.
- Renal Disorder: Signifies kidney involvement, met by persistent protein in the urine (greater than 0.5 grams per day or a score of 3+). Alternatively, the presence of cellular casts in a urine sample meets this criterion.
- Neurologic Disorder: Satisfied by the occurrence of seizures or psychosis, provided these symptoms are not caused by an unrelated drug or a known metabolic imbalance. These manifestations reflect inflammation within the central nervous system.
- Hematologic Disorder: Evidence of a blood cell abnormality, such as hemolytic anemia, or a consistently low white blood cell count (leukopenia or lymphopenia) or platelet count (thrombocytopenia). Leukopenia and lymphopenia must be documented on at least two occasions.
- Immunologic Disorder: The presence of specific autoantibodies, such as anti-double-stranded DNA (anti-dsDNA) antibodies, anti-Smith (anti-Sm) antibodies, or antiphospholipid antibodies. These antibodies are characteristic of SLE.
- Antinuclear Antibody (ANA): A positive ANA test, an almost universal finding in SLE patients, indicating the immune system targets components within the cell’s nucleus.
How the Criteria Determine Classification
The 11 ACR criteria were fundamentally designed for patient classification, not for routine clinical diagnosis. Their primary purpose is to ensure that researchers enrolling patients into clinical trials are studying a relatively uniform group. To be classified as having SLE under the ACR 1997 criteria, an individual must exhibit four or more of the 11 specified criteria. These four or more criteria can be present either at the same time or sequentially over any period of observation.
This classification system, while highly specific for research, differs significantly from a clinical diagnosis made by a physician. A rheumatologist may diagnose a patient with SLE even if they do not meet the four-out-of-eleven threshold, relying instead on clinical judgment, the pattern of organ involvement, and the overall severity of the disease. Conversely, meeting four criteria does not automatically guarantee a diagnosis, as other conditions can mimic some of these manifestations.
The Shift to Modern Diagnostic Systems
Despite their foundational importance, the 11 ACR criteria began to show limitations, particularly in identifying patients with early or milder disease. The criteria were developed based on patients with established, often severe, SLE, leading to a relatively low sensitivity for those presenting with less pronounced symptoms. The reliance on discrete, unweighted criteria also failed to account for the varying severity and importance of different organ involvements.
In response to these limitations, the Systemic Lupus International Collaborating Clinics (SLICC) introduced a revised set of classification criteria in 2012. The SLICC criteria aimed to increase sensitivity, particularly by including more specific immunologic findings. Following this, the European League Against Rheumatism and the American College of Rheumatology (EULAR/ACR) collaborated to publish new classification criteria in 2019. These modern criteria represent a significant departure from the original list by employing a weighted scoring system.
The EULAR/ACR 2019 system requires a positive ANA test as an obligatory entry criterion; without it, the patient is generally not classified as having SLE. Once this entry criterion is met, points are assigned to various clinical and immunologic manifestations based on their statistical association with the disease. The criteria are grouped into domains, and a patient’s total score must reach a threshold of 10 or more points to be classified as having SLE. This weighted, additive approach provides a more sensitive and nuanced tool for classifying patients, particularly those with early disease.