This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunomodulator, Subject name: Pharmacology
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? 
Select and explain. 
A. Complete blood count, B. Uric acid, C. G6PD, D. PPD skin test
D: PPD skin test
Answer: D: PPD skin test 
Explanation: Answer: d) PPD skin test* The patient is having rheumatoid arthritis which is diagnosed by the positive anti-CCP levels on serology.* Biological disease modifying anti rheumatoid drugs include following TNF a inhibitors: Infliximab, Etanercept, Adalimumab, Golimumab* Infliximab is chimeric monoclonal antibody while Adalimumab & Golimumab are human monoclonal antibodies.* Anti TNF agents are to be avoided in active infections and hypersensitivity reactions.* There is an increased risk of opportunistic infections and flare up of latent tuberculosis.* Hence obtaining a purified PPD skin test is a mandatory requirement for starting TNF a inhibitors.