American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the synovial fluid leukocyte count associated with inflammatory states?

1. Less than 200/µL

2. 200/µL to 2000/µL

3. Greater than 2000/µL

4. Greater than 5000/µL

The correct answer is: Greater than 2000/µL

The synovial fluid leukocyte count is an important diagnostic tool for assessing the presence of inflammatory states in joint conditions. In cases of inflammatory arthropathies, such as rheumatoid arthritis or gout, the leukocyte count in the synovial fluid typically reflects an active inflammatory process. A count greater than 2000/µL is indicative of significant inflammation within the joint. This elevated leukocyte count generally consists of a predominance of neutrophils, especially in cases of septic arthritis. Counts in this range signal that the body's immune system is actively responding to a perceived threat, whether that be infection, crystal deposition, or an autoimmune process. Counts below this threshold, such as those less than 200/µL or in the range of 200 to 2000/µL, suggest either a non-inflammatory condition (such as osteoarthritis) or less severe inflammation. Thus, the selection of a count greater than 2000/µL is specifically characteristic of more pronounced inflammatory states. This fact makes it clear that greater counts correlate with more severe forms of inflammation.