# Diagnostic work-up in periprosthetic joint infections of the knee: can the albumin-to-globulin ratio be a screening tool?

## TL;DR

This study explores whether the albumin-to-globulin ratio (AGR) can help identify knee joint infections after surgery.

## Contribution

The study proposes a new AGR threshold (1.43) for screening periprosthetic joint infections.

## Key findings

- An AGR cutoff of 1.43 showed 95% sensitivity and 63% specificity for detecting infections.
- AGR had a high negative predictive value of 91%, making it useful for ruling out infections.
- No significant predictors of false positives were identified despite some confounding factors.

## Abstract

This study aimed to assess the most appropriate thresholds for albumin-to-globulin ratio (AGR) in patients who had a suspected periprosthetic knee infection. Furthermore, the diagnostic accuracy of the proposed threshold was evaluated.

Between January 2020 and April 2022, patients with failed or painful knee arthroplasty who were admitted to a tertiary referral institution undergoing the standardized diagnostic protocol to identify those with a periprosthetic joint infection (PJI) were analyzed. The 2018 International Consensus Meeting (ICM) criteria were used to classify patients with PJIs and aseptic joints. Sensitivity, specificity, positive predictive value, negative predictive value, and the area under the receiver operating characteristic (ROC) curve (AUC) of AGR were calculated to define the test’s diagnostic accuracy.

The ROC curve showed that the optimal cutoff value of AGR was 1.43. AGR registered a sensitivity of 95% (95% CI 91–197%), a specificity of 63% (95% CI 56–69%), a positive predictive value of 75% (95% CI 69–81%), and a negative predictive value of 91% (95% CI 86–94%). Receiver operator curve analysis demonstrated an AUC of 0.85 (95% CI 0.77–0.88). Although body mass index (BMI), uremia, glutamic-oxaloacetic transaminase (GOT), international normalized ratio (INR), and alkaline phosphatase showed significant differences between the false positive cases and those cases affected by aseptic failure with AGR higher than 1.43, indicating potential confounding effects (p < 0.05), no parameter was found to be a significant predictor of false positives cases (p > 0.05).

For its high sensitivity, AGR showed potential as a screening tool for detecting infections in PJI diagnostics.

Level of evidence: III.