How is dx of non-gonococcal arthritis?

Arthrocentesis (synovial fluid gram stain, WBC, and culture. Staph/strep are 91% of infections, gram - are in old and immunocompromised pt, gram + 71% of cases are +, 40-50% of cases are gram - and <25% gonococcal, microscopy for only 50% of cases) Lab markers (WBC, ESR, CRP) Imaging (Radio normal early stages, only swelling, structural damage severity differs according to agent, include juxta-articular osteoporosis, diffuse joint space narrowing due to cartilage destruction and erosions, at late stages appear badly destroyed, MRI/CT assesses inflammation, destruction and periarticular soft tissue masses)