Evaluation of white blood cell concentration, plasma fibrinogen concentration, and an agar gel immunodiffusion test for early identification of foals with Rhodococcus equi pneumonia.

The research article assesses whether WBC concentration, plasma fibrinogen concentration, and an AGID test can early identify foals with Rhodococcus equi pneumonia. It concludes that monitoring WBC concentration is beneficial for the detection, while the AGID test isn’t that useful.

Study Design and Methods

• This article is describing a prospective study aimed at evaluating whether measurements of a foal’s White Blood Cell (WBC) concentration, plasma fibrinogen concentration, and the results of an Agar Gel Immunodiffusion (AGID) test can assist in the early identification of Rhodococcus equi pneumonia in foals.
• The study involved 162 foals from a farm with an endemic R. equi infection and involved regularly taking blood samples from each foal at various intervals for different measurements.
• These measurements and tests included measuring WBC and plasma fibrinogen concentration at 4-week intervals, and anti-R. equi antibody detection using an AGID assay every 2 weeks.
• The diagnostic performance of the WBC and fibrinogen concentrations was assessed using receiver operating characteristic curve analysis. This type of analysis measures how well a parameter or test can distinguish between diagnostic categories.
• The study used bacteriologic culture of R. equi from tracheobronchial aspirates as the reference test to establish the presence of R. equi infection.

Results and Conclusion

• The results showed that the diagnostic performance of the WBC concentration was significantly higher than that of the fibrinogen concentration. Thus, it was a more effective tool for identifying R. equi infection.
• The sensitivity (the ability of the test to correctly identify infected foals) and specificity (the ability of the test to correctly identify non-infected foals) of the WBC concentration varied depending on the chosen cutoff point.
• It was found that a cutoff of 13,000 cells per microliter yielded a sensitivity of 95.2% and a specificity of 61.2%. While, a higher cutoff of 15,000 cells per microliter, decreased sensitivity to 78.6%, but increased specificity to 90.8%.
• The AGID assay showed limited effectiveness with a sensitivity of 62.5% and a specificity of 53.8%, making it relatively unreliable for this purpose.
• Consequently, the study concluded that monitoring WBC concentration is a useful method of early detection of R. equi infection in foals, especially in settings where there is a high incidence of R. equi pneumonia. However, the AGID assay was found to have limited benefit for the same purpose.