A 45-year-old male patient presents with symmetric small joint swelling and pain accompanied by morning stiffness for 3 years. Over the past 3 months, symptoms have worsened with prolonged morning stiffness, dry cough, shortness of breath, and dyspnea on exertion (no paroxysmal nocturnal dyspnea). Physical examination reveals swollen and tender wrists and metacarpophalangeal joints, reduced grip strength, painless subcutaneous nodules on both elbows, and Velcro rales in the lower lung fields. Which additional tests are needed to confirm the diagnosis?