American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the typical leukocyte count in joints infected with bacteria?

1. 2000/µL

2. 25,000/µL

3. 50,000/µL

4. 75,000/µL

The correct answer is: 50,000/µL

In cases of bacterial infection within the joints, known as septic arthritis, the leukocyte count is typically elevated significantly. A leukocyte count of 50,000/µL is consistent with the inflammatory response seen in bacterial infections, particularly when neutrophils are predominantly present. This reflects the body's effort to combat the infection through an escalation of immune cells to the site of inflammation. Other counts, such as 2000/µL, would generally indicate a much milder inflammatory process or a non-infectious cause, while counts of 25,000/µL and 75,000/µL suggest intermediate or extreme reactions that might not represent the most common scenario for bacterial joint infections. Thus, 50,000/µL serves as a clinical benchmark for septic arthritis and correlates well with the typical presentation of this condition.