What is the result of the Systemic Lupus Erythematosus (SLE) test?

From the Guidelines

The SLE test, or systemic lupus erythematosus test, is a combination of blood tests used to diagnose lupus, with the antinuclear antibody (ANA) test being the most important, and additional tests such as anti-double-stranded DNA (anti-dsDNA) and anti-Smith (anti-Sm) antibodies being more specific for lupus. The diagnosis of lupus is based on a combination of clinical symptoms and laboratory tests, including the ANA test, which is positive in about 98% of lupus patients 1. If ANA is positive, additional tests are typically performed, including anti-dsDNA and anti-Sm antibodies, which are more specific for lupus. Other helpful tests include complete blood count, comprehensive metabolic panel, erythrocyte sedimentation rate, C-reactive protein, complement levels (C3 and C4), and urinalysis.

The management of SLE aims at remission or low disease activity and prevention of flares, with hydroxychloroquine recommended in all patients with lupus, at a dose not exceeding 5 mg/kg real body weight 1. The use of anti-dsDNA autoantibodies in the diagnosis and follow-up of SLE is also important, with a recent study proposing recommendations for their use 1. The study highlights the importance of selecting the most adequate assay and an appropriate interpretation of results, as well as the need for standardization of autoantibody assays.

Some key points to consider when ordering SLE tests include:

• The ANA test is the most sensitive test for lupus, but it can also be positive in other conditions, such as rheumatoid arthritis or scleroderma 1.
• The anti-dsDNA test is more specific for lupus, but it can also be positive in other conditions, such as mixed connective tissue disease 1.
• The anti-Sm test is highly specific for lupus, but it is only positive in about 20-30% of lupus patients 1.
• Other tests, such as complete blood count and comprehensive metabolic panel, can help to evaluate the patient's overall health and detect any potential complications of lupus.

Testing should be ordered when patients present with symptoms suggestive of lupus, such as joint pain, skin rashes, fatigue, or unexplained fever. Results should always be interpreted by a healthcare provider in the context of the patient's overall clinical picture, as false positives can occur in other conditions. The updated recommendations for the management of SLE, including the use of hydroxychloroquine and immunomodulatory agents, can help to improve patient outcomes and reduce the risk of complications 1.

From the Research

SLE Test Overview

• Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that can affect multiple organs and tissues 2.
• The diagnosis of SLE is based on a combination of clinical and laboratory criteria, including the presence of antinuclear antibodies (ANA) 3, 4.

Diagnostic Criteria

• The American College of Rheumatology specifies that four of 11 clinical and laboratory criteria must be met to establish a diagnosis of SLE 3.
• The ANA test is the primary laboratory test used to diagnose SLE, but it is not specific for the disease and must be interpreted in the appropriate clinical context 4.
• Other diagnostic tests, such as antibody to double-stranded DNA antigen and antibody to Sm nuclear antigen, may be used to support the diagnosis of SLE 3.

Laboratory Tests

• The ANA test is positive in nearly every case of SLE, but it can also be positive in other autoimmune diseases and in healthy individuals 4, 5.
• The erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and procalcitonin (PCT) may be used to detect infections in patients with SLE, but their utility is limited by poor sensitivities and specificities 6.
• The levels of anti-DNA antibodies can fluctuate widely and may reflect disease activity, whereas anti-RBP antibodies tend to be stable 5.

Clinical Considerations

• The diagnosis of SLE should be considered in patients with unexplained multisystem inflammatory disease, symmetric joint pain with inflammatory features, photosensitive rash, and cytopenias 4.
• The clinical context is important in interpreting the results of laboratory tests, and a single test result should not be used to establish a diagnosis of SLE 3, 4.