What is the expected white blood cell count in a joint aspiration for septic arthritis?

In cases of septic arthritis, the expected white blood cell (WBC) count in joint aspiration typically shows a very high level of leukocytes, often exceeding 50,000 cells per microliter. This elevated count reflects the intense inflammatory response and the presence of infection within the joint space. The majority of these leukocytes are neutrophils, which are the body’s primary defense against bacterial infections.

When diagnosing septic arthritis, clinicians often rely on this significant elevation in WBC count as a crucial indicator. Counts above 50,000 are consistent with the clinical presentation of septic arthritis, such as painful swelling of the joint, fever, and difficulty moving the affected limb. Therefore, a count over 50,000 WBCs is an important marker that guides treatment decisions and helps differentiate septic arthritis from other conditions that may cause joint swelling, such as inflammatory arthritis or crystal-induced arthritis, which typically present with lower WBC counts.