What laboratory finding typically supports the diagnosis of septic arthritis in a joint?

• A. Low leukocyte count with lymphocyte predominance
• B. Presence of crystalline structure in synovial fluid
• C. Increased leukocyte count primarily with neutrophils
• D. Decreased protein levels in synovial fluid

Answer: (C)

The presence of an increased leukocyte count primarily with neutrophils in synovial fluid is a key laboratory finding indicative of septic arthritis. In cases of septic arthritis, it is common to see an elevated number of white blood cells due to the inflammatory response triggered by an infection in the joint. Neutrophils are typically the predominant leukocyte type in the synovial fluid during bacterial infections, as they are the primary responders to the presence of bacteria.

This neutrophilic response is a direct reflection of the body's immune reaction to the invading pathogens, and analyzing the synovial fluid through arthrocentesis often reveals a leukocyte count exceeding 50,000 cells/mm³, with a high percentage of neutrophils. Therefore, finding a predominance of neutrophils in the synovial fluid supports the diagnosis of septic arthritis.

Other findings, such as a low leukocyte count with lymphocyte predominance, would be more suggestive of viral infections or chronic inflammation rather than acute bacterial infection. The presence of crystalline structures in synovial fluid would typically indicate conditions like gout or pseudogout rather than septic arthritis. Lastly, decreased protein levels in synovial fluid are generally associated with non-inflammatory or less inflammatory conditions, whereas