Paper of the week: Plasma Viscosity Has a Role in the Diagnosis of Prosthetic Joint Infection After Total Knee Arthroplasty. Bajada S, Yoong AWH, Hourigan P, Koopmans PC, Phillips JRA, Toms AD. J Arthroplasty. 2019 Jul 30. pii: S0883-5403(19)30719-3. doi: 10.1016/j.arth.2019.07.035.

Summary by Dr Sreeram Penna

This retrospective study aimed to find out the clinical value of plasma viscosity in the diagnosis of periprosthetic joint infection (PJI) in painful total knee arthroplasty patients. Primarily researchers compared value of plasma viscosity with erythrocyte sedimentation rate (ESR) and c reactive protein (CRP). Patients with inflammatory arthropathies and lymphoproliferative disorders were excluded from the study. Researchers used MSIS criteria for diagnosing infection.

The results of the study showed that there is a strong correlation between plasma viscosity and ESR and CRP. Based on the study data, plasma viscosity value of 1.81 mPa.s. had the best efficacy. Utilizing this value sensitivity, specificity, positive likely hood ration, and negative likely hood ratio of plasma viscosity in PJI was 58.3%, 93.8%, 9.43, and 0.44, respectively. When comparing plasma viscosity to ESR in patients with both serum investigations available (107 patients), the area under the curve (AUC) was 0.814 for plasma viscosity while AUC for ESR was 0.812 — showing that PV is noninferior to ESR as a reliable screening test.

The advantages of plasma viscosity compared to ESR as suggested by authors include plasma viscosity not influenced by hematocrit (anemia, polycythemia), red blood cell aggregation, hemoglobinopathies, anti-inflammatory medication, or time to analysis, patients age. In addition, the authors mention that the plasma viscosity test is cheaper than ESR and CRP.