Basics of RA Diagnostics
Rheumatoid Arthritis is diagnosed by:
Taking a medical history.
Performing a physical exam.
Ordering laboratory tests.
Ordering imaging studies, such as x-rays or ultrasound.
Rheumatoid arthritis. National Institute of Arthritis and Musculoskeletal and Skin Diseases. June 5, 2025. Accessed September 21, 2026. https://www.niams.nih.gov/health-topics/rheumatoid-arthritis/diagnosis-treatment-and-steps-to-take.
What is ESR, and why is it elevated in RA?
Erythrocyte sedimentation rate measures how fast RBCs settle in a tube over an hour. It's elevated in RA because inflammation raises fibrinogen and other acute-phase proteins in the blood, causing RBCs to clump and fall faster.
What is CRP, and why is it elevated in RA?
C-reactive protein is an acute-phase protein produced by the liver. It's elevated in RA because inflamed synovium releases IL-6, which drives CRP production.
What are the joints highlighted in yellow?
Distal interphalangeal joints
What is the characteristic X-ray appearance of rheumatoid arthritis? (joint involvement, erosion pattern, distribution)
RA characteristically shows MCP joint involvement greater than IP, marginal erosions, and a polyarticular distribution.
Ezzati F, Pezeshk P. Radiographic findings of inflammatory arthritis and mimics in the hands. Diagnostics (Basel, Switzerland). September 2, 2022. Accessed September 21, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC9498090/.
It can be difficult to diagnose rheumatoid arthritis when it is in the early stages because:
Symptoms (pain, stiffness, fatigue) are nonspecific and overlap with other conditions
Classic findings (nodules, deformities, erosions) haven't developed yet
RF/anti-CCP can be negative early despite true RA
X-rays are often normal before erosions develop
Symptoms may be intermittent/migratory rather than persistent and symmetric
No single test confirms the disease
What does a positive rheumatoid factor titer indicate?
It means the immune system is producing autoantibodies (typically IgM) against IgG's Fc portion — supportive of RA, but not fully specific.
What is anti-CCP, and why is it elevated in RA?
Anticyclic citrullinated peptide is an autoantibody against citrullinated proteins formed during inflammation. It's elevated because the immune system targets these self-proteins, and it's more specific for RA than RF.
What are the joints highlighted in blue?
Proximal interphalangeal joints
What is the characteristic X-ray appearance of psoriatic arthritis? (joint involvement, erosion pattern, distribution)
PsA characteristically shows IP joint involvement greater than MCP, erosions that are marginal progressing to central, and a distribution that is two-thirds asymmetric and mono-oligoarticular.
Ezzati F, Pezeshk P. Radiographic findings of inflammatory arthritis and mimics in the hands. Diagnostics (Basel, Switzerland). September 2, 2022. Accessed September 21, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC9498090/.
What is arthrocentesis?
Arthrocentesis is the procedure where a needle is inserted into a joint space to aspirate synovial fluid for diagnostic analysis or therapeutic drainage/injection.
What is ANA, and why is it elevated in RA?
Antinuclear antibody is an autoantibody against nuclear components, sometimes mildly positive in RA; mainly checked to screen for overlapping lupus.
What is SS, and why is it elevated in RA?
SS-A/SS-B (anti-Ro/anti-La) are autoantibodies linked to secondary Sjögren's syndrome, which commonly co-occurs with RA.
What are the joints highlighted in green?
Metacarpophalangeal joints
What is the characteristic X-ray appearance of osteoarthritis? (joint involvement, erosion pattern, distribution)
OA characteristically shows IP joint involvement greater than MCP (predominantly DIP), central erosions, and a polyarticular, bilateral, usually symmetric distribution.
Ezzati F, Pezeshk P. Radiographic findings of inflammatory arthritis and mimics in the hands. Diagnostics (Basel, Switzerland). September 2, 2022. Accessed September 21, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC9498090/.
What lab results would differ in Osteoarthritis compared to Rheumatoid Arthritis?
OA usually has normal ESR/CRP and negative RF/anti-CCP.
What lab results would differ in Psoriatic Arthritis compared to Rheumatoid Arthritis?
PsA is usually RF/anti-CCP-negative, and ESR/CRP may stay normal or mild even with active disease.
What are the key structural components of a synovial joint, and what is the function of each?
Synovial cavity – space with synovial fluid; reduces friction
Articular cartilage – cushions bone ends; smooths movement
Ligaments – bone-to-bone; stabilize, limit motion
Synovial membrane – secretes synovial fluid; lubricates, nourishes cartilage
Capsule – encloses joint; provides stability
Identify the type of arthritis shown in the X-ray.
“76-year-old female with erosive arthritis. Severe osteoarthritis of most of the distal and proximal interphalangeal joints with central erosions and seagull appearance.”
“60-year-old female with long-standing rheumatoid arthritis. Hand radiographs shows erosive changes in the PIP and MCP joints as well as the wrist. Ulnar subluxation of the fingers at MCP joints is also present. Note the distal interphalangeal joints are spared.”
“79-year-old male with psoriatic arthritis. Hand radiographs demonstrate diffuse soft-tissue swelling in the index finger (sausage finger). Small marginal erosions are present in the DIP joint along with mild fluffy periosteal reaction.”
Ezzati F, Pezeshk P. Radiographic findings of inflammatory arthritis and mimics in the hands. Diagnostics (Basel, Switzerland). September 2, 2022. Accessed September 21, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC9498090/.
What drives citrullination, and why does smoking raise anti-CCP risk?
Peptidylarginine deiminase (PAD) enzymes convert arginine to citrulline in proteins; smoking upregulates PAD activity in the lungs, generating neoantigens that trigger anti-CCP in susceptible individuals (especially those with HLA-DRB1 shared epitope alleles).
What is seronegative RA, and how is it diagnosed/managed?
RA meeting clinical/imaging criteria despite negative RF/anti-CCP; diagnosis relies more on exam and imaging, with the same treat-to-target DMARD management.
What type of synovial joint are the metacarpophalangeal and proximal interphalangeal joints, and how does that affect their range of motion?
MCP joints are condyloid joints, allowing flexion/extension plus some side-to-side movement. PIP joints are hinge joints, allowing flexion/extension only.