Laboratory Workup for Suspected Infectious Arthritis

Essential Initial Laboratory Tests

The American College of Physicians and the Infectious Diseases Society of America recommend that ESR and CRP should be obtained in all patients with suspected infectious arthritis, as the combination provides the best sensitivity and specificity for diagnosis 1
The European League Against Rheumatism suggests that CBC with differential should be obtained to evaluate for systemic infection and leukocytosis 3
The Infectious Diseases Society of America recommends that arthrocentesis should be performed in all patients with suspected acute infectious arthritis unless the diagnosis is clinically evident and surgery is already planned, and that synovial fluid analysis must include total cell count and differential leukocyte count, Gram stain, and aerobic and anaerobic cultures 1
The American Academy of Orthopaedic Surgeons notes that crystal analysis should be performed to exclude crystal arthropathy, which can coexist with infection 5

The National Institute for Health and Care Excellence recommends that urinalysis, transaminases, and renal function tests should be obtained as baseline assessments before potential antibiotic therapy 3, 4, 6
The American College of Rheumatology suggests that antinuclear antibodies, rheumatoid factor, and anti-CCP antibodies should be obtained if the diagnosis is uncertain or if autoimmune diseases are suspected 3, 4, 6

The Infectious Diseases Society of America recommends that interleukin-6 and synovial fluid alpha-defensin can be used as advanced biomarkers for prosthetic joint infections, with synovial fluid alpha-defensin providing high accuracy 2

The American Academy of Orthopaedic Surgeons advises against delaying arthrocentesis, as synovial fluid analysis is required to confirm diagnosis and cannot be replaced by serum markers alone 1, 5
The Infectious Diseases Society of America recommends against starting antibiotics before obtaining cultures when clinically feasible, as this significantly reduces organism recovery 1, 2

The American College of Physicians recommends that baseline values, including CRP, ESR, and CBC, should be obtained prior to initiating treatment, and that serial monitoring of inflammatory markers helps assess treatment response 2