The combined evaluation of fibrinogen and D-dimer levels helps to exclude periprosthetic knee infection: study

Balato et al found in a retrospective study that a D-dimer level >1063 ng/ml combined with a fibrinogen level >420 mg/dl had a sensitivity of 0.52, and a specificity of 0.90. An increased D‐dimer beyond 1063 ng/ml showed a better predictive value than the previously proposed threshold. The combined determination of D‐dimer and fibrinogen displayed high specificity and should be considered an excellent tool to rule out an infection. The accuracy of the proposed cutoffs is more effective than previously reported.

This observational cohort study included consecutive patients who had undergone total knee arthroplasty (TKA) revision. International Consensus Meeting diagnostic criteria were used to identify patients affected by the prosthetic infection. Receiver operating characteristic curve analyses assessed the predictive value of the parameters, and the areas under the curves were evaluated. 125 patients with a median age of 69 years (53–82) affected by painful TKA were included.

Key findings of the study:

• Fifty‐ seven patients (47%) had PJI.

• Known comorbidities relating to an increased infection risk were reported in 39% (49 of 125) of patients, and diabetes mellitus was identified with the highest frequency.

• Thirty patients had a BMI greater than 30 kg/m2, and the remaining 95 had a BMI below 30 kg/m2.

• Patients with PJI had higher median D‐dimer, fibrinogen, ESR, and CRP when compared to patients believed to be free of PJI.

• Based on the criteria specified above, 57 (45%) knees were judged to be infected.

• Positive cultures were obtained in 41/57 cases (72%).

• The most common microorganisms identified by positive cultures were coagulase‐negative staphylococci (54%), followed by Staphylococcus aureus (11%). Gram‐negative bacteria were isolated from 15 percent of the patients.

• The best threshold values for D‐dimer and fibrinogen were 1063 ng/ml (sensitivity 0.72, specificity 0.74) and 420 mg/dl (sensitivity 0.67 and specificity 0.82), respectively.

The authors concluded that – “The combined test of D‐dimer and fibrinogen is an excellent tool to exclude infection, as it displays high specificity.”

Further reading:

Balato G, Ascione T, Festa E, et al. The combined evaluation of fibrinogen and D‐dimer levels are a helpful tool to exclude periprosthetic knee infection. J Orthop Res. 2023;1‐8. doi:10.1002/jor.25515