Alpha Defensin: A Diagnostic Accuracy Depending on the Infection Definition Used

The purpose of this study was to evaluate the alpha defensin qualitative detection (ADLF) sensitivity and specificity as compared with 3 standard classifications in the diagnostic management of chronic prosthetic joint infections.

A multicenter cohort of 136 patients with a painful arthroplasty was classified into either infected or noninfected according to the Musculoskeletal Infection Society (MSIS) score, Infectious Diseases Society of America (IDSA) score, European Bone and Joint Infection Society (EBJIS) score. The sensitivity and specificity of the ADLF test were calculated for each score. Spearman’s correlations between all scores were then analyzed, and multiple logistic regression was applied to identify independent variables strongly connected to the prosthetic joint infection probability.

The EBJIS score was positive in 68 patients, IDSA score in 50 patients, MSIS score in 41 patients, and ADLF in 40 patients. The ADLF sensitivity was 87.8% compared with MSIS, 70% compared with IDSA, and 55.8% compared with EBJIS. The ADLF specificity was in the range of 94%-97%. A good correlation was observed between synovial fluid cultures and ADLF ( r = 0.73). Low to excellent correlations were recorded between ADLF and the EBJIS ( r = 0.58), IDSA ( r = 0.68), and MSIS ( r = 0.84) scores. The synovial fluid’s white blood cell count was proven to be the biological test that most influenced the probability of a positive culture ( P value: .005).

The ADLF sensitivity was variable, whereas its specificity was excellent. The EBJIS score results significantly differed from those obtained via cultures, which possibly explains the ADLF low sensitivity compared with that of the EBJIS score.