A20 year old female has an erythematous rash over her face on both cheeks and across the bridge of her nose.This rash is made worse by sunlight exposure when she is outdoors. Along with the rash, she has had muscle and joint pain for several month. However, radiographs of the joints does not show any abnormalities, and she has normal joint mobility without deformity. Which of the following laboratory test findings is most characteristic of the disease?

**Core Concept**
The patient's symptoms suggest a diagnosis of **Systemic Lupus Erythematosus (SLE)**, a chronic autoimmune disease characterized by **inflammation** and **autoantibody production**. The butterfly-shaped rash on the face, known as a **malar rash**, is a classic symptom of SLE.

**Why the Correct Answer is Right**
The correct answer is related to the presence of **antinuclear antibodies (ANA)**, which are a hallmark of SLE. ANA are **autoantibodies** that target the cell nucleus and are found in nearly all patients with SLE. The presence of ANA is a sensitive marker for SLE, although it is not specific to the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Is incorrect because while **rheumatoid factor** may be present in some patients with SLE, it is not as sensitive or specific as ANA for the diagnosis of SLE.
**Option B:** Is incorrect because **anti-citrullinated protein antibody (anti-CCP)** is more commonly associated with **rheumatoid arthritis**.
**Option C:** Is incorrect because **anti-neutrophil cytoplasmic antibody (ANCA)** is more commonly associated with **vasculitis**.

**Why Each Wrong Option is Incorrect (continued)**
**Option D:** Is incorrect because while **anti-dsDNA** antibodies are specific for SLE, they are not as sensitive as ANA for the diagnosis of SLE.

**Clinical Pearl / High-Yield Fact**
The presence of ANA is a key diagnostic criterion for SLE, and a positive ANA test is often used as a screening test for the disease.

**Correct Answer:** D. Anti-nuclear antibody (ANA)

✓ Correct Answer: D. Antibodies to double-standed DNA