A 30 year old lady presents to the outpatient department with an erythematous butterfly rash on her cheeks. Which of the following antibodies should be assayed initially for her suspected condition:
**Core Concept**
The patient's presentation of an erythematous butterfly rash on her cheeks is suggestive of Systemic Lupus Erythematosus (SLE), a chronic autoimmune disease characterized by inflammation and damage to multiple organs. The disease is mediated by the production of autoantibodies against nuclear antigens.
**Why the Correct Answer is Right**
The initial diagnostic step for SLE involves detecting the presence of antinuclear antibodies (ANA), which are a hallmark of the disease. The ANA test detects the presence of autoantibodies directed against various nuclear components, including histones, DNA, and other proteins. A positive ANA result supports the diagnosis of SLE and guides further testing to confirm the diagnosis. The ANA test is highly sensitive but not specific, as it can be positive in other autoimmune diseases as well.
**Why Each Wrong Option is Incorrect**
**Option A:** Anti-Sm antibodies are specific for SLE but are not the initial test to be ordered. They are a subset of ANA and are used to confirm the diagnosis in patients with a positive ANA result.
**Option B:** Anti-SSA/Ro antibodies are associated with Sjögren's syndrome, an autoimmune disorder that affects the exocrine glands.
**Option C:** Anti-CCP antibodies are specific for rheumatoid arthritis, an autoimmune disease that primarily affects the joints.
**Option D:** Anti-HCV antibodies are used to diagnose hepatitis C infection, a viral disease that affects the liver.
**Clinical Pearl / High-Yield Fact**
ANA is a sensitive but not specific test for SLE. A positive ANA result should be interpreted in the context of the patient's clinical presentation and other laboratory findings.
**Correct Answer:** A. Antinuclear antibody (ANA) test.