Clues from history and physical examination	Diagnoses to consider	Evaluation
Active range of motion restricted more than passive range of motion	Periarticular pathology	Radiography and/or MRI if indicated
Back pain, eye inflammation	Ankylosing spondylitis	HLA-B27 testing, radiography
Coagulopathy, use of anticoagulants	Hemarthrosis	CBC, ESR, arthrocentesis to confirm diagnosis and rule out infection
Diuretic medication, presence of tophi, renal stones	Gout	CBC, ESR, uric acid level, arthrocentesis with evaluation for crystals
Hilar adenopathy, erythema nodosum	Sarcoidosis	CBC, ESR, ACE level, chest radiography, pulmonary referral
Immunosuppression and/or intravenous drug abuse	Septic arthritis	CBC, ESR, arthrocentesis for cell count and cultures
Insidious onset of pain and swelling over days to weeks	Indolent infection, osteoarthritis, infiltrative disease, tumor	CBC, ESR, arthrocentesis for cell count and cultures, radiography and possible MRI if tumor is a consideration
Maximum pain at limits of range of motion (i.e., stress pain)	Osteoarthritis	Radiography
Normal joint examination	Referred pain	Consider alternative diagnosis
Onset of pain and swelling over several hours or one to two days	Infection, crystal deposition disease, other inflammatory arthritic condition	CBC, ESR, uric acid level, arthrocentesis with evaluation for crystals
Pain elicited by joint movements against resistance only	Tendinitis, bursitis	MRI or ultrasonography if diagnosis in question
Previous acute attacks in any joint with spontaneous resolution	Crystal deposition disease, other inflammatory arthritic condition	CBC, ESR, uric acid level, arthrocentesis with evaluation for crystals
Prolonged course of corticosteroid therapy	Infection, avascular necrosis	CBC, ESR, arthrocentesis for cell count and cultures if concern for infection, radiography and possible MRI if considering avascular necrosis
Psoriatic skin plaques, nail pitting, dactylitis	Psoriatic arthritis	CBC, ESR, arthrocentesis, HLA-B27 testing, ANA testing; none of these tests are diagnostic but can exclude other conditions
Restricted active and passive range of motion	Intra-articular pathology	Radiography and/or MRI if indicated
Sudden onset of pain in seconds or minutes	Fracture, internal derangement, trauma, loose body	Radiography
Urethritis, conjunctivitis, diarrhea, rash, sacroiliitis	Reactive arthritis	CBC; ESR; arthrocentesis; HLA-B27 testing; urine PCR testing for Chlamydia trachomatis; stool cultures for Salmonella, Shigella, and Campylobacter
Young adult, migratory polyarthralgias, tendons inflamed	Gonococcal arthritis	Urine PCR testing, blood culture, and synovial fluid analysis for Neisseria gonorrhoeae