Test Catalog

Test ID: ALDEF    
Alpha Defensin, Lateral Flow Assay, Synovial Fluid

Useful For Suggests clinical disorders or settings where the test may be helpful

Detection of alpha defensins 1-3, human host response proteins, in synovial fluid of adults with a total joint replacement who are being evaluated for revision surgery


This test is not intended to be used to determine timing for reimplantation in 2-stage procedures.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Diagnosis of prosthetic joint infections (PJI) may be challenging in certain clinical scenarios. Multiple societies have defined criteria for establishing the presence of a PJI, including results from laboratory tests, clinical findings, and tissue histopathology. The challenge, however, is that results of these tests are frequently not available at the time of or after surgery. As an alternative, determining the cell count and differential on synovial fluid are frequently used biomarkers for PJI, however there is a lack of consensus on the optimal thresholds to use for a PJI diagnosis. Additionally, cell count and differential results require clinician interpretation as laboratories do not report abnormal levels correlating with PJI.


Alpha defensins are antimicrobial peptides released by activated neutrophils in response to infection and served as part of the host-defense innate immune system with broad antimicrobial activity against Gram-positive and Gram-negative bacteria, mycobacteria, fungi, and viruses. The presence of alpha defensins in synovial fluid may therefore be used by clinicians as a marker of PJI.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results


No alpha defensin detected in synovial fluid, suggesting absence of prosthetic joint infection.



Alpha defensin in synovial fluid detected suggesting presence of prosthetic joint infection. Additional microbiologic studies (eg, culture, molecular detection) are recommended.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Alpha defensin testing should be used to evaluate for the presence of a prosthetic joint infection if other clinical and diagnostic test findings (ie, synovial fluid cell count and differential) are inconclusive.

Test results should be utilized in conjunction with other clinical and diagnostic findings to aid the diagnosis of prosthetic joint infection (PJI).


This kit has been developed for use with freshly collected synovial fluid only. The use of this test kit with any other specimen type may lead to inaccurate test results. The use of synovial fluid diluted with saline, blood, contrast agent, or any substances injected into the joint may lead to false–negative results.


Presence of red blood cells (RBCs), greater than 1 million/mcL, in the synovial fluid specimen may lead to false–negative results. This represents dilution of the synovial fluid specimen with greater than 20% blood.


The performance of this test has only been validated for conditions evaluated by the Musculoskeletal Infection Society (MSIS) criteria.


A decrease in sensitivity (an increased likelihood of false-negative results) has been observed in the presence of a sinus tract communicating with the prosthesis. Since the presence of a sinus tract is definitive evidence of PJI, use of this test under those circumstances is not recommended.


False-positive results have been reported in the presence of metallosis.


A negative test result does not preclude the possibility of infection.


Synovial fluid obtained after repeated aspirations within a short time period might lead to false–negative results due to the lack of buildup of alpha defensin.

Clinical Reference Recommendations for in-depth reading of a clinical nature

Bonanzinga T, Ferrari MC, Tanzi G, et al: The role of alpha defensin in prosthetic join infection (PJI) diagnosis: a literature review. EFFORT Open Rev 2019;4:10-13