BACKGROUND

Periprosthetic joint infection (PJI) remains diagnostically challenging. Synovial calprotectin is a rapid point-of-care biomarker with promising diagnostic accuracy, but its added diagnostic and clinical value remains unclear.

 

AIM

To evaluate the added diagnostic and clinical value of synovial calprotectin in patients with suspected PJI.

 

METHODS

Study design: Prospective two-center observational study of consecutive patients undergoing joint aspiration for suspected hip or knee PJI (January 2023–July 2024).

Calprotectin testing: Synovial calprotectin was measured using the Lyfstone point-of-care lateral flow test (positive ≥14mg/L). The treating surgeon was blinded to the results.

Classification and evaluation: Patients were classified using the 2018 MSIS and 2021 EBJIS criteria at initial assessment (T0) and at last follow-up (T1, through August 2026).

Analysis: Diagnostic accuracy was assessed against definitive T1 classifications; diagnostically uncertain cases were analyzed separately. T0 uncertain cases were additionally evaluated in a hypothetical calprotectin-informed pathway to estimate potential changes in management.

 

RESULTS

Study population (n=75)

Calprotectin results

18 positive (24%)

57 negative (76%)

 

CALPROTECTIN PERFORMANCE VS MSIS AT T1, % (95% CI)

Sensitivity Specificity PPV NPV

93.8 (69.8–99.8) 100 (93.4–100) 100 (78.2–100) 98.2 (90.3–100)

 

CALPROTECTIN PERFORMANCE VS EBJIS AT T1, % (95% CI)

Sensitivity Specificity PPV NPV

81.0 (58.1–94.6) 100 (93.0–100) 100 (80.5–100) 92.7 (82.4–98.0)

 

CALPROTECTIN PERFORMANCE IN UNCERTAIN CASES AT T0, % (95% CI)

Sensitivity Specificity PPV NPV

100 (29.2–100) 77.8 (40.0–97.2) 60.0 (14.7–94.7) 100 (59.0–100)

Calprotectin-informed assessment could have changed

management in 4 patients.

 

CONCLUSION

Synovial calprotectin showed high diagnostic accuracy, with

excellent specificity under both MSIS and EBJIS criteria. Its

added value may lie particularly in diagnostically uncertain

cases, where it may support classification, inform clinical

decision-making, and potentially reduce additional diagnostic

testing.