July 14, 2017
3 min read

Predictive value of infection after TJA improved with alpha-defensin test

Research may focus on how the alpha-defensin test performs in patients with added comorbidities.

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SAN DIEGO — When its use is considered in addition to the traditional test results for periprosthetic joint infection, the alpha-defensin test improved the ability to predict positive cultures both when the traditional tests were equivocal or when they were all aligned toward one diagnosis, according to Gregory S. Kazarian, BA.

Kazarian, Carl A. Deirmengian, MD, and colleagues studied the predictive value of the alpha-defensin test for infection after total joint arthroplasty.

In his presentation at the American Academy of Orthopaedic Surgeons Annual Meeting, Deirmengian said, “Alpha-defensin seems to have made a big difference when considered in the context of the other [Musculoskeletal Infection Society] MSIS tests. All the P values were extremely significant here and you see that no matter what your other tests are showing, the alpha-defensin provided an incremental benefit to the interpretation of that patient’s labs.”

Carl A. Deirmengian, MD
Carl A. Deirmengian

Kazarian, a medical student at Washington University in St. Louis, said, “The alpha-defensin test is not only useful as a high accuracy individual test for [periprosthetic joint infection] PJI, but also has a marked effect on the likelihood of a positive culture when considered in the context of traditional test results.”

Diagnostic benefits of test

Deirmengian and his colleagues collected 8,382 synovial fluid samples from patients who underwent hip and knee arthroplasty and had a complete set of synovial fluid laboratory studies that included alpha-defensin, C-reactive protein, white blood cell count, percent of polymorphonuclear cells and cultures. Researchers categorized patients into three groups based on whether the synovial fluid laboratory tests for PJI were all negative (n=4,872), all positive (n=1,299) or mixed (n=2,211).

Results showed a culture positivity rate that was less than 1% in the all negative group, 8.3% in the mixed group and 61.3% in the all positive group. Researchers then looked at the alpha-defensin test to determine if it added any clinical diagnostic benefit in these populations.

When added to the traditional tests for infection, a positive alpha-defensin result was found to associate with statistically significant increases in the likelihood of having a positive culture, ranging from 5.1-fold to 13.8-fold.

“The group of patients with mixed traditional laboratory test results showed the greatest difference, as a negative alpha-defensin result was associated with a 2.6% rate of positive culture, whereas a positive alpha-defensin result was associated with a 36.1% rate of positive cultures. This was statistically significant and demonstrated a nearly 14-times greater likelihood of PJI when the alpha-defensin test is positive,” Kazarian said.


Subgroups examined

Deirmengian, of the Rothman Institute in Philadelphia, told Orthopedics Today the research was meant to determine whether the alpha-defensin test would improve the diagnostic capacity of the many tests that are already in use for what the MSIS defines as PJI.

“What we wanted to know is if you are already ordering all of the other tests, does it make sense to also order alpha-defensin? Does it add anything?” Deirmengian told Orthopedics Today. “The study showed it did, even when all the traditional tests were aligned toward the same diagnosis,” he said.

Deirmengian noted that future research should include patient subgroups not looked at previously, including patients with gout and rheumatoid arthritis.

“We are continuing to evaluate the performance of alpha-defensin in subgroups now,” Deirmengian said. “We know the alpha-defensin [test] works in a big population of patients, but there are subgroups we know less about.” – by Casey Tingle

Disclosures: Deirmengian reports he is a paid consultant for Zimmer Biomet; receives stock/stock options from Biostar Ventures Trice and Domain; is a paid presenter/speaker for Zimmer Biomet; and receives research support from Zimmer Biomet. Kazarian reports no relevant financial disclosures.