Why Fibrinogen Increases in Periprosthetic Joint Infection
Fibrinogen increases as part of the acute phase inflammatory response to bacterial infection, serving as a key mediator of inflammation in periprosthetic joint infection (PJI). 1
Mechanism of Fibrinogen Elevation
Fibrinogen is an acute phase reactant that rises in response to bacterial infection through the following pathway:
- Bacterial infection triggers systemic inflammation, causing hepatic synthesis of acute phase proteins including fibrinogen, which plays a direct role in mediating the inflammatory response to bacterial pathogens 1
- Fibrinogen has a longer half-life than CRP, making it particularly useful for detecting chronic or low-grade infections where the inflammatory response may be more sustained 2
- The elevation correlates with infection severity, with higher levels indicating active bacterial infection rather than mechanical complications 1, 3
Diagnostic Utility in PJI
When combined with ESR and CRP, fibrinogen achieves exceptional diagnostic accuracy:
- Using cutoffs of fibrinogen >432 mg/dL, ESR >27 mm/h, and CRP >0.93 mg/L, abnormality in at least 2 of 3 tests yields 93% sensitivity, 100% specificity, and 97% accuracy for PJI diagnosis 4, 2
- Fibrinogen at 519 mg/dL demonstrates 90% sensitivity (though only 34% specificity when used alone), making it most valuable as part of a multi-marker approach 1
- Fibrinogen performs significantly better than traditional markers like peripheral WBC count, which remains normal in most PJI cases 4, 5
Clinical Context and Interpretation
The fibrinogen elevation must be interpreted within the clinical picture:
- Night pain or pain at rest suggests infection (where fibrinogen elevation is expected), whereas pain only with weight-bearing suggests mechanical loosening (where fibrinogen should be normal) 4, 5
- CRP typically returns to baseline within 2 months after uncomplicated arthroplasty, so persistent elevation of fibrinogen beyond this timeframe strongly suggests infection 4, 2
- Fibrinogen elevation is more specific to bacterial infection than ESR alone, which can be elevated in uninfected patients with mechanical complications 4
Comparison to Other Inflammatory Markers
Fibrinogen demonstrates superior performance compared to fibrinolytic markers:
- D-dimer and fibrin degradation products (FDP) show limited diagnostic value with sensitivities of only 68% and 65% respectively, and are inferior to traditional inflammatory markers 6
- Fibrinogen outperforms ESR and CRP in predicting reinfection after debridement procedures, with 81.82% sensitivity and 83.33% specificity in acute PJI 7
- Globulin, albumin-to-globulin ratio, and fibrinogen all demonstrate strong diagnostic performance (AUC 0.820,0.845, and 0.832 respectively) 3
Common Pitfalls to Avoid
- Never rely on fibrinogen alone—it must be combined with ESR and CRP for optimal accuracy, as isolated elevation has poor specificity 4, 1
- Do not interpret fibrinogen elevation without considering the postoperative timeline—normal postoperative elevation can persist for up to 2 months 4, 8
- Avoid premature testing—fibrinogen peaks during hospital stay after two-stage exchange and returns to baseline by 90-180 days, so timing of measurement affects interpretation 8