D-Dimer Blood Test Detects Prosthetic Joint Infections as Accurately as Standard Tests

Diagnosing PJI can be highly challenging because there is no single test that can claim to have 100% accuracy in determining or ruling out its presence. C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), which are two common markers of inflammation, are recommended as screening tests for patients suspected of having PJI. However, both these markers have limitations, such as a high rate of false-negative results when PJI is present. Plasma D-dimer, a test commonly used for certain blood clot-related disorders, is also a potentially useful marker of infection and has been validated for use in the diagnosis of PJI. However, some studies have raised concerns over the diagnostic performance of D-dimer testing for PJI, and its true accuracy is still unknown. Now, a new study suggests that the measurement of plasma D-dimer levels can provide useful information when making the difficult diagnosis of PJI.

In the new study, researchers at Thomas Jefferson University (Philadelphia, PA, USA) compared plasma D-dimer and other tests for the diagnosis of PJI. Over a four-year period, the study prospectively enrolled 502 patients undergoing revision knee or hip arthroplasty, irrespective of their surgical indication. All the patients underwent a blood draw just before their surgery to measure their levels of D-dimer, CRP, and ESR, and fibrinogen. After applying the 2018 International Consensus Meeting definition of PJI, the researchers found 23% of the patients had PJI. The four tests had "comparable accuracy" for the diagnosis of PJI. Sensitivity (ability to detect PJI when present) was 81.3% for D-dimer, 90.4% for CRP, 73.9% for ESR, and 74.7% for fibrinogen. On the other hand, specificity (correctly showing that PJI was not present) was 81.7% for D-dimer, 70.0% for CRP, 85.2% for ESR, and 75.4% for fibrinogen. For all four measures, the values were higher for patients who were shown to have PJI.

However, in some patient subgroups, D-dimer offered a diagnostic advantage. In a sub-analysis that excluded patients with certain health conditions associated with inflammation, the D-dimer test outperformed ESR, fibrinogen, and CRP in recognizing the presence of PJI. D-dimer also performed best in detecting PJI caused by slow-growing "indolent" organisms, with higher values for both sensitivity and specificity. Additionally, all the four tests showed a better diagnostic performance in patients with suspected PJI in the knee, as compared with PJI in the hip. The report is the largest prospective study evaluating the performance of different laboratory tests for suspected PJI and support D-dimer testing as a valuable tool for the often-difficult diagnosis of PJI. There is a need for further studies, and no universal diagnostic cutoff point can be determined due to known variations in D-dimer measurement, according to the researchers.

"We found that plasma D-dimer was noninferior to serum CRP and ESR in the diagnosis of PJI and may be a useful adjunct when screening patients undergoing revision total joint arthroplasty," said Javad Parvizi, MD, FRCS, and colleagues of Rothman Orthopedic Institute at Thomas Jefferson University.

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