Paziuk T, Rondon AJ, Goswami K, Tan TL, Parvizi J.

The Journal of Arthroplasty. 2020 Mar 1;35(3):836–9.
DOI: 10.1016/j.arth.2019.10.012

Summary by Mohammad S. Abdelaal MD, MSc

Investigation of prosthetic joint infection (PJI) remains a challenge that requires a combination of various qualitative and quantitative tools in order to reach accurate diagnosis [1][2]. The role that platelets play in our bodies’ innate response to both inflammation and infection has been extensively studied [3][4]. Circulating platelets are able to directly facilitate the body’s response to infection, as they possess the ability to scavenge and collect microbial invaders in a way that supports the function of leukocytes [5].The purpose of this study was to determine if two commonly ordered laboratory values associated with platelets, absolute platelet count (PC) and mean platelet volume (MPV), could potentially aid in the diagnostic workup of patients with suspected PJI.

Paziuk et al retrospectively reviewed all cases of revision total hip arthroplasty (THA) and total knee arthroplasty (TKA) performed between 2000 and 2016 at a single institution. Their cohort included 949 patients with chronic PJI, as defined by the Musculoskeletal Infection Society criteria, and 3,989 patients with aseptic failures. PC and MPV were calculated from each patient preoperative blood count using Sysmex XN analyzer. The diagnostic performance of the platelet parameters were assessed and then compared to the ROC curve analyses of both ESR and CRP. Their results showed higher PC/MPV ratio in PJI patients compared to patients of aseptic revision (33.45 vs 25.68) (P < 0.001). ROC curve analysis demonstrated that an optimal ratio of 31.70 has a sensitivity of 48.10 (95% confidence interval 44.9-51.4) and a specificity of 80.85 (95% confidence interval 79.6-82.1) with an area under the curve (AUC) of 0.69. The specificity for the PC/MPV ratio was greater than the specificity for both ESR and CRP using optimal values determined via ROC curve analysis; however, the diagnostic performance of PC/MPV ratio was less than that of either ESR or CRP. When the ratio was used with both ESR and CRP, as opposed to just using ESR and CRP, there was a significant improvement in diagnostic accuracy of the assessment (P < .05). They concluded that PC/MPV ratio is a routinely available adjunct test that could be useful in the workup of potential PJI.

Acknowledged limitations included retrospective nature of the study which could have introduced some selection bias. In addition, there might have been an opportunity for variability in how PC and MPV were collected and calculated over the duration of this study.

References:

1. P. Alijanipour, H. Bakhshi, and J. Parvizi, “Diagnosis of periprosthetic joint infection: the threshold for serological markers,” Clin. Orthop. Relat. Res., vol. 471, no. 10, pp. 3186–3195, Oct. 2013, doi: 10.1007/s11999-013-3070-z.
2. J. Parvizi et al., “The 2018 Definition of Periprosthetic Hip and Knee Infection: An Evidence-Based and Validated Criteria,” J Arthroplasty, vol. 33, no. 5, pp. 1309-1314.e2, 2018, doi: 10.1016/j.arth.2018.02.078.
3. S. Zareifar, M. R. Farahmand Far, F. Golfeshan, and N. Cohan, “Changes in platelet count and mean platelet volume during infectious and inflammatory disease and their correlation with ESR and CRP,” J. Clin. Lab. Anal., vol. 28, no. 3, pp. 245–248, May 2014, doi: 10.1002/jcla.21673.
4. M. H. F. Klinger and W. Jelkmann, “Review: Role of Blood Platelets in Infection and Inflammation,” Journal of Interferon & Cytokine Research, vol. 22, no. 9, pp. 913–922, Sep. 2002, doi: 10.1089/10799900260286623.
5. F. Gaertner et al., “Migrating Platelets Are Mechano-scavengers that Collect and Bundle Bacteria,” Cell, vol. 171, no. 6, pp. 1368-1382.e23, Nov. 2017, doi: 10.1016/j.cell.2017.11.001.