Diagnosis	Joint distribution	Synovial fluid findings
		WBC count*	Gram stain/culture	Synovial fluid crystals†	Radiography findings
Gout	Lower extremities: metatarsophalangeal, midtarsal, or knee joints; initial attacks may be less common in upper extremities	2,000 to 50,000 per mm3 (2 × 109 to 50 × 109 per L)	Negative	Needle shaped, negative birefringence	Acute: asymmetric swelling
					Chronic: periarticular erosions with overhanging edges
Pseudogout (calcium pyrophosphate deposition disease)	Knee, wrist, or first metatarsophalangeal	2,000 to 50,000 per mm3	Negative	Rhomboid shaped, weak positive birefringence	Soft tissue swelling, chondrocalcinosis (calcification of cartilage)
Septic arthritis	Knee is most commonly involved (may be any joint distribution)	< 50,000 per mm3	Positive	No crystals	Joint effusion; radiography results otherwise normal early in the disease