Equine Science Update: Potential new marker for joint infection

Synovial infections, involving joints and tendon sheaths, are a potentially serious condition in
horses. Early diagnosis and treatment are essential. If not treated promptly, the infection can cause permanent damage to the joint with potentially career-ending and, indeed, life-threatening consequences.

Usually, a diagnosis of joint infection is confirmed on the basis of synovial fluid analysis - typically looking at the white blood cell count and protein levels.

Scientists at the University of Copenhagen have been investigating the potential of neutrophil gelatinase-associate lipocalin (NGAL) as a marker for synovial sepsis

NGAL (also known – among other things- as Lipocalin-2) is a protein that is produced in response to injury or inflammation. It is involved in many processes in the body and plays a part in the non-specific immune defences. It acts to limit bacterial growth by sequestering iron, which is required for bacterial growth. Originally identified in neutrophils, it can be produced in other cells, such as kidney tubule cells, in response to damage. In human medicine it has been used for early diagnosis of acute renal injury, and it has been suggested to be a highly sensitive and specific marker of joint infection.

Stine Jacobsen and co-workers measured NGAL concentrations in 177 synovial fluid samples obtained from 152 horses suspected of having synovial infection. The aim of the study was to investigate NGAL concentrations in synovial fluid from horses with septic synovitis, horses without septic synovitis, and horses with uncertain status. A full report is published in Animals.

The authors explain that, based on the results from the clinical and diagnostic workup on the day of admission, horses were divided into three groups:

(1) septic synovitis, defined as a white blood cell count (WBC) >30 × 109/L leukocytes and one (or both) of the following: total protein (TP) >30 g/L and neutrophil granulocyte percentage (neutrophil%) >90. Horses were also defined as septic if there was a positive bacteriology result, (47 samples)

(2) non-septic, defined as WBC <5 × 109/L leukocytes, (103 samples), and

(3) uncertain, defined as WBC >5 and <30 × 109/L leukocytes. (27 samples).

They found that concentrations of NGAL were significantly higher in the septic synovitis group than in samples classified as non-septic or samples with uncertain status, with median NGAL concentrations in the three groups being 1236, 16.8, and 266.4 µg/L, respectively.

“NGAL discriminated nearly perfectly between septic and non-septic (area under the receiver operating characteristic curve 0.98, 95% confidence interval 0.95–1.00)” they report.

“The optimal cut-off value for maximal sensitivity (87.2%) and specificity (75.0%) to discriminate septic samples from those with uncertain status was 444.6 µg/L, with an area under the receiver operating characteristic curve of 0.85 (95% confidence interval 0.74–0.93).”

For 35 horses the scientists tested more than one sample taken over the course of treatment. They found that NGAL concentrations declined over time in horses undergoing treatment.

They conclude “NGAL is a novel biomarker that seems to have great potential for identifying septic synovitis and for monitoring the response to treatment of synovial infection in horses.”

For more details, see:

Gelatinase-Associated Lipocalin in Synovial Fluid from Horses with and without Septic Arthritis.

Stine Jacobsen, Camilla Drejer Mortensen, Elisabeth Alkærsig Høj, Anne Mette Vinther, Lise Charlotte Berg, Ditte Marie Top Adler, Denis Verwilghen, and Gaby van Galen. 2023. Neutrophil

Animals (2023) 13, no. 1: 29.

https://doi.org/10.3390/ani13010029

(Open access article published under a Creative Commons licence)