A 45 year old female presents with the complaint of pain in the metacarpophalangeal, proximal interphalangeal and metatarsophalangeal joints of both right and left hands. Serology showed positive anti-CCP antibodies. She was placed on infliximab for control. Which of the following need to tested before starting treatment?

**Core Concept:** Rheumatoid Arthritis is an autoimmune disorder characterised by chronic inflammation of synovial joints, leading to pain, swelling, and deformity. Anti-citrullinated protein antibodies (anti-CCP) are a specific marker for rheumatoid arthritis and are used for its diagnosis and monitoring.

**Why the Correct Answer is Right:**

The correct answer, **D. Rheumatoid Arthritis**, is chosen because the patient presents with symptoms consistent with the disease, including pain in multiple joints and positive serology (anti-CCP antibodies). Infliximab is a biologic DMARD (disease modifying antirheumatic drug) used to treat rheumatoid arthritis by inhibiting TNF-alpha (tumor necrosis factor-alpha), a pro-inflammatory cytokine involved in joint inflammation.

**Why Each Wrong Option is Incorrect:**

A. **Autoimmune Disorders**: Although the patient is suffering from an autoimmune disorder, testing for a single autoimmune disease cannot confirm it as the correct diagnosis.

B. **Inflammatory Arthritis**: This option is too broad and does not specifically address the patient's symptoms or the positive anti-CCP antibodies.

C. **Infectious Arthritis**: This option is unrelated to the patient's symptoms and positive anti-CCP antibodies.

**Why the Correct Answer is Right:**

Rheumatoid arthritis is the correct answer because the patient's symptoms and serological findings (positive anti-CCP antibodies) align with the clinical presentation of rheumatoid arthritis. Infliximab is a suitable treatment for rheumatoid arthritis as it targets TNF-alpha, which plays a role in joint inflammation.

**Why Each Wrong Option is Incorrect:**

A. **Autoimmune Disorders**: Although the patient is suffering from an autoimmune disorder, testing for a single autoimmune disease cannot confirm it as the correct diagnosis.

B. **Inflammatory Arthritis**: This option is too broad and does not specifically address the patient's symptoms or the positive anti-CCP antibodies.

C. **Infectious Arthritis**: This option is unrelated to the patient's symptoms and positive anti-CCP antibodies.

✓ Correct Answer: D. PPD skin test