Will White Blood Cell (WBC) count be elevated in septic arthritis?

From the Guidelines

Yes, white blood cell (WBC) count is typically elevated in septic arthritis, with a count of at least 12,000 cells/mm3 being one of the Kocher criteria used to distinguish septic arthritis from transient synovitis 1.

Key Points to Consider

• The Kocher criteria, which include fever, erythrocyte sedimentation rate, WBC count, and an inability to bear weight on the affected side, are widely applied in the evaluation of septic arthritis 1.
• Elevated C-reactive protein >2.0 mg/dL has also been described as an accurate predictor of septic arthritis 1.
• The diagnosis of septic arthritis is made by arthrocentesis, and clinical suspicion is of paramount importance in management 1.
• Typical management of septic arthritis consists of antibiotics, arthrotomy, irrigation, and debridement 1.

Important Considerations

• The distribution of septic arthritis and osteomyelitis varies by age, with children <2 years of age being more likely to have septic arthritis than osteomyelitis 1.
• Imaging plays a critical role in characterizing and differentiating septic arthritis from osteomyelitis 1.
• The body mounts an immune response to the bacterial infection in the joint, recruiting white blood cells to fight the infection, resulting in an elevated WBC count 1.

Diagnostic Approach

• Both blood and synovial fluid should be collected for WBC count, culture, and other analyses before starting antibiotics 1.
• The definitive diagnosis of septic arthritis comes from identifying the causative organism through synovial fluid culture 1.
• While elevated WBCs strongly suggest septic arthritis, it is essential to consider other diagnostic criteria and laboratory results to confirm the diagnosis 1.

From the Research

White Blood Cell Count in Septic Arthritis

• The White Blood Cell (WBC) count is often used as an indicator of septic arthritis, but its reliability as a diagnostic tool is debated 2, 3, 4, 5, 6.
• A synovial fluid WBC count greater than 50,000 cells/mm^3 is commonly considered indicative of septic arthritis, but this cutoff value is not universally accepted 2, 3, 4, 6.
• Studies have shown that patients with septic arthritis can have varying WBC counts, and some may even have low WBC counts 4, 5.
• The sensitivity of an elevated WBC count in diagnosing septic arthritis is relatively low, ranging from 48% to 64% 5.
• Other laboratory tests, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), may also be used in conjunction with WBC count to aid in diagnosis, but their effectiveness is also limited 4, 5.

Variability in WBC Count

• WBC counts can vary widely in patients with septic arthritis, making it difficult to rely solely on this test for diagnosis 3, 4, 5.
• Some patients with septic arthritis may have WBC counts less than 50,000 cells/mm^3, while others may have much higher counts 3, 4, 5.
• The presence of other conditions, such as gout, can also affect WBC counts and make diagnosis more challenging 3.

Diagnostic Challenges

• Diagnosing septic arthritis can be difficult, and laboratory tests, including WBC count, may not always be reliable 2, 3, 4, 5, 6.
• A combination of clinical presentation, laboratory tests, and synovial fluid analysis is often necessary to make an accurate diagnosis 2, 3, 4, 5, 6.
• The cornerstones of treating septic bacterial arthritis are adequate drainage and antimicrobials, and joint drainage is always recommended 6.