Periprosthetic Joint Infection: No Role for Antibody Testing?

A new retrospective study has been published that calls into question the utility of synovial fluid antibody assay testing for some common pathogens.

The study, “Commercial Synovial Antibody Testing is No Better Than Traditional Culture in Identification of Pathogen(s) Causing Periprosthetic Joint Infection,” appears in the December 27, 2021, edition of The Journal of Arthroplasty.

According to co-author Javad Parvizi, M.D., director of Clinical Research at the Rothman Orthopaedic Institute, this review was prompted by a newly available testing service which could, in effect, double check the accuracy of antibody assay testing.

He explained to OTW, “A commercial entity has recently started to perform antibody testing on samples that are sent to them for measurement of a molecular marker (alpha defensin). The reports coming back from that commercial entity reports the presence or absence of some common pathogens as detected by culture and antibody testing.”

“We had noted that in a group of patients in whom alpha defensin was negative and patients by definitions were unlikely to have infection, had positive antibody testing for some pathogens including fungi. The latter presents ethical and legal issues in that whether the patient should or should not be treated and what would happen if the positive test was ignored. As the utility of the antibody test was not validated by an independent authority, we decided to evaluate the role of this test in our patients.”

The researchers looked at 419 patients who had revision total hip and knee arthroplasty (January 2019-2020). Using the International Consensus Meeting criteria as reference standard for periprosthetic joint infection (PJI), the authors found that “antibody testing had a sensitivity of 40.5% and a specificity of 93.4%. There were 59.5% false negative results with antibody testing compared with 50% for culture. Of the 12 patients who had positive results for both tests, 5 (41.7%) had discordant pathogens identified in each test.”

We asked Dr. Parvizi if he was surprised by these results. He said, “Not really. As suspected, we found that there were patients with infection in whom the antibody test was negative and some patients with infection being unlikely in whom the antibody test was positive.”

“Clinicians sending samples to the commercial entity for the measurement of alpha defensin need to be aware that the same company does perform antibody testing on those samples also and may provide the report together with the alpha defensin analyses. Based on our study, there is little to no role for having the antibody testing done.”