Poor performance of monocyte-to-lymphocyte ratio, neutrophil-to-lymphocyte ratio, and fibrinogen when screening for occult infection among patients with sequelae of suppurative hip arthritis before total hip arthroplasty

Background Total hip arthroplasty (THA) is considered the best treatment for sequelae of suppurative hip arthritis, but such patients are more likely to have occult infection and therefore to suffer post-operative periprosthetic joint infection. Our study examined (1) the occult infection rate among patients with sequelae of suppurative hip arthritis, and whether (2) neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), or fibrinogen levels can be used to screen such patients for occult infection before THA. Methods We retrospectively enrolled 428 patients who underwent primary THA at our hospital between 2010 and 2021, of whom 31 had occult infection and 397 did not. The maximum sensitivity and specificity were determined for the three indicators using receiver operating characteristic curves, and positive and negative predictive values were calculated. Results Patients with occult infection showed significantly higher erythrocyte sedimentation rate (ESR) and higher levels of C-reactive protein (CRP) and fibrinogen than those without occult infection. The various potential indicators gave the following areas under the receiver operating characteristic curves: ESR, 0.586; CRP, 0.599; interleukin-6, 0.651; NLR, 0.506; MLR, 0.600; and fibrinogen, 0.589. Sensitivity and specificity were as follows: ESR, 30.8% and 92.5%; CRP, 50.0% and 70.2%; interleukin-6, 57.7% and 67.5%; NLR, 46.7% and 62.9%; MLR, 60.0% and 61.7%; and fibrinogen, 43.3% and 81.7%. Conclusion The rate of occult infection was 7.24% among our patients. ESR, NLR, MLR, and levels of CRP, interleukin-6, and fibrinogen may be unreliable for screening such patients for occult infection before THA according to sensitivity and specificity.