Soluble Urokinase Plasminogen Activator Receptor (SuPAR)

Analysis for Diagnosis of Periprosthetic Joint Infection

 

Introduction

Periprosthetic joint infection (PJI) affects at least 2% of joint replacements and is a growing

clinical and economic burden as arthroplasty volumes rise. Synovial white blood cell count

remains the diagnostic gold standard, but soluble urokinase plasminogen activator receptor

(suPAR) — an inflammation marker already used in sepsis and cardiac disease — has never been

evaluated in synovial fluid.

This study investigates whether suPAR in blood plasma and synovial fluid can serve as a diagnostic

biomarker for PJI, using the EBJIS criteria as reference standard.

Methods

Study design: Retrospective single-centre cohort, Jan 2019–Oct 2021; 60 adult patients, 67 joint

punctures (knee 82%, hip 16%, shoulder 2%)

Case definition: PJI classified per European Bone and Joint Infection Society (EBJIS) criteria by a

blinded assessor

Laboratory analyses: Blood: WBC (whole blood), CRP (plasma), suPAR (plasma) · Synovial fluid: suPAR

(ELISA)

Statistical approach: ROC analysis; optimal cut-offs by Youden’s J; diagnostic performance reported as

PPV and NPV

Results

Of 67 samples, 43 (64%) met EBJIS criteria for PJI and 24 (36%) were PJI-negative. Synovial cell

count, plasma CRP, and synovial suPAR were all significantly higher in infected joints (p ≤ 0.002);

plasma WBC and plasma suPAR did not differ between groups (p ≥ 0.132).

Conclusion

▪ Synovial suPAR shows solid diagnostic performance, comparable to plasma CRP, and may serve as an

alternative or complementary biomarker for PJI.

▪ Plasma suPAR was highly specific but poorly sensitive — not suitable as a stand-alone screening test.

▪ An automated, non-cytological suPAR assay could shorten laboratory turnaround versus manual

synovial cell counting.

▪ Findings require validation in larger, prospective, multi-centre cohorts.

 

K E Y T A K E A W A Y

Synovial suPAR performs on par with plasma CRP and needs no cytology expertise — a fast,

objective candidate to complement synovial cell count in PJI work-up.