The C-Reactive Protein Combination Ratios Outperform the Albumin-Globulin Ratio in Diagnosing Periprosthetic Joint Infection After Total Knee Arthroplasty.

BACKGROUND

Obtaining an accurate preoperative diagnosis of periprosthetic joint infections (PJI) is challenging, making differentiating between septic and aseptic failures difficult. We sought to identify the value of common serum biomarkers and evaluate the accuracy of three ratios in the diagnosis of PJI after primary total knee arthroplasty (TKA): albumin-globulin ratio (AGR), C-reactive protein-albumin ratio (CAR), and C-reactive protein-AGR ratio (CAGR).

METHODS

Patients undergoing PJI and aseptic revisions after TKA between 2011 and 2021 were retrospectively reviewed at a single institution. Only patients who had reported serum white blood cell, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), albumin (Alb), and total protein (TP) were included. Areas under the curve (AUCs), which optimize diagnostic performance by balancing sensitivity and specificity at a specific cutoff, were calculated for each individual biomarker and the three ratio groups: AGR = Alb/[TP - Alb], CAR = CRP/Alb, and CAGR = CRP/AGR. Higher AUCs indicate improved identification of PJI while reducing misclassification. Of the 126 included cases, 89 were confirmed PJIs, and 37 were aseptic revisions.

RESULTS

Among the single and combination serum biomarkers, the AUCs were as follows: CRP (0.85), ESR (0.76), Alb (0.81), AGR (0.78), CAR (0.87), and CAGR (0.87). The CAR demonstrated excellent accuracy at a cutoff of 2.46, with a sensitivity of 0.74 and specificity of 0.84. CAGR also demonstrated excellent accuracy at a cutoff of 7.09, with a sensitivity of 0.80 and specificity of 0.78.

CONCLUSIONS

The CRP, CAR, and CAGR showed an excellent diagnostic accuracy as markers for PJI. In patients undergoing revision TKA, common serum biomarkers, such as Alb, TP, CRP, and ESR, can be obtained, and CAR or CAGR ratios can be calculated to aid in the diagnosis of PJI, especially in cases where synovial analysis is inconclusive, allowing for better clinical decision-making.