No added value of the neutrophil-lymphocyte ratio (NLR) and platelet count to mean platelet volume ratio (PC/MPV) over the traditional serum markers (ESR and CRP) in the diagnosis of periprosthetic joint infection (PJI).

PURPOSE

Several serum biomarkers have been used to aid in the diagnosis of PJI including Platelet count/mean platelet Volume Ratio (PC/MPV) and neutrophil to lymphocyte ratio (NLR). The purpose of this study is to report the diagnostic performance of the serum markers NLR and PC/MPV in periprosthetic joint infection and to compare these markers with other already established serum biomarkers as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and other synovial biomarkers as synovial white blood cell counts (WBCs), polymorphonuclear leucocyte percentage (PMN%), leucocyte esterase and synovial culture.

METHODS

This is a single centre prospective cohort study in which all patients with painful Hip or Knee arthroplasty presented to our clinic whether they underwent a revision surgery or not were evaluated for eligibility. Out of 145 patients with painful hip or knee arthroplasty that were evaluated, 35 patients were excluded leaving 110 patients with eligible for this study. Blood samples were taken within a week before the revision surgery or aspiration to obtain the following parameters: ESR, CRP, WBCs, NLR, PC, MPV and PC/MPV. The modified Musculoskeletal Infection Society (MSIS) criteria were set as the gold standard test for diagnosis of periprosthetic joint infection (PJI) in the study.

RESULTS

According to the MSIS criteria, 48 of them were septic and 62 were aseptic. The diagnostic accuracy of the new serum markers was lower than that of the traditional markers. Receiver-operator characteristic (ROC) curve analysis for the NLR showed an area under the curve (AUC) of 0.556 with p-value = 0.321, for the PC/MPV showed an AUC of 0.586 with p-value = 0.129 while that for ESR showed an AUC of 0.688 with p-value = 0.001 and that for CRP showed an AUC of 0.778 with p-value < 0.001. To determine whether adding each of NLR and PC/MPV to the traditional serum markers (ESR + CRP) would increase the diagnostic performance of these markers or not. we compared the four models: (1) ESR + CRP, (2) ESR + CRP + NLR, (3) ESR + CRP + PC/MPV and (4) ESR + CRP + NLR + PC/MPV. there was no significant difference between the four models in AUC which shows that no added value of using the new serum markers.

CONCLUSION

Traditional serum markers (ESR and CRP) still have the best diagnostic performance in the diagnosis of PJI even when compared to the newer markers as NLR and PC/MPV which show limited added value either alone or when combined with ESR + CRP.

LEVEL OF EVIDENCE

Level I, diagnostic study.