Synovial Fluid NGAL Accurately Diagnoses Prosthetic Joint Infection

The previous use of antimicrobial therapies will significantly decrease the sensitivities of either serum or the synovial fluid (SF) biomarkers. Inaccurate diagnosis may lead to incorrect treatment options and poor prognosis. Neutrophil gelatinase-associated lipocalin (NGAL) has been used for the early identification of bacterial and viral infections in blood and cerebrospinal fluid.

Orthopaedic Surgeons at the Fujian Medical University (Fuzhou, China) included in a prospective study in a single osteoarticular infection referral center, in which consecutive patients who needed revision surgery after hip and knee arthroplasty due to PJI or aseptic prosthesis loosening from January 2017 to September 2018. A total of 78 patients who underwent hip or knee revision surgery were included in the study.

The scientists collected 0.5 mL of the SF for the white blood cell count (SF-WBC) and neutrophil classification. A total of 1 mL of the SF was frozen at -80 °C for NGAL determination. The remaining SF was used for microbiological culture. SF was injected into Bactec Plus/F aerobic or Bactec Peds Plus/F blood culture bottles and anaerobic blood culture bottles (Becton-Dickinson, Heidelberg Germany). The plates and bottles were incubated for 14 days in a Bactec 9050 automatic incubator.

The periprosthetic tissue was cut into pieces, added to the broth for grinding, and then cultured for aerobic and anaerobic bacteria on a blood plate for 14 days. The Vitek II system (bioMérieux, Durham, NC, USA) was used for microbial identification and antibiotic susceptibility testing. The SF samples were centrifuged and diluted appropriately before assaying. The team determined NGAL levels using the NGAL Duo Set ELISA Kits (R&D Systems, Minneapolis, MN, USA). The level of NGAL in the SF was measured in duplicate.

The investigators reported that a total of 50 of 78 included patients were diagnosed with PJI. A total of 40 cases were positively cultured. The most common pathogen was Staphylococcus aureus in 10 (25%) patients, followed by coagulase-negative staphylococci in seven patients, and gram-negative bacilli in seven patients (17.5%), and other pathogens in 16 patients. The median SF-NGAL level was 3,633 ng/mL (interquartile range [IQR], 1,332-10,737) in the PJI group and 26.8 ng/mL (IQR, 12.4-52.5) in the aseptic failure group. When the SF-NGAL threshold was 263 ng/mL, the area under the curve was 0.98, the sensitivity was 92.9%, and the specificity was 98%. The median level was 5,779 ng/mL (IQR, 1425-13,072) in the antibiotic group and 2,590 ng/mL (IQR, 932-8,970) in the non-antibiotic group.

The authors concluded that NGAL in the SF has both high sensitivity and specificity for the PJI diagnostics. The previous use of antibiotics does not affect the level of the SF-NGAL. The SF-NGAL can be used as a potential laboratory indicator for diagnosing PJI. The study was published on October 1, 2022 in the International Journal of Infectious Diseases.