According to the original Kocher criteria for differentiating pediatric septic arthritis of the hip from transient synovitis, which of the following is considered one of the four classic predictive variables?

Explanation:
The original Kocher criteria (published in 1999) consist of four predictive factors for pediatric septic arthritis of the hip: non-weight-bearing on the affected side, ESR > 40 mm/hr, fever > 38.5°C (101.3°F), and a serum WBC count > 12,000 cells/mm³. If all four criteria are present, the predicted probability of septic arthritis is 99%. CRP > 2.0 mg/dL was later added in modified versions of the criteria but was not one of the original four. Reference: Tachdjian's Pediatric Orthopaedics, 6th Edition.