EQUINE INTERNAL MEDICINE: FROM ASCARIDS TO ZEBRAS


Fig. 5. A histogram representation of fibrinogen concentration of Regressors (blue) and Progressors (red) across all ultrasonographic grades, where the x-axis shows fibrinogen levels and the y-axis shows the number of patients affected.


narian satisfaction with the program’s ability to decrease the incidence of clinical cases. Although clients may not be enamored with the expense of the screening, costs and side-effects of antibiotic ther- apy, management changes due to treatment proto- cols and ethical repercussion of overtreating, many are justifiably reluctant to make program changes that could increase the risk of clinical disease. After reaching a satisfactory level of clinical disease on an endemic property, it is also difficult for veter- inarians to recommend changes to an established screening program that may increase the risk to individuals. The goal of this study was to expand the approach


of screening programs to improve veterinarians’ ability to predict which individuals would develop clinical R. equi pneumonia. The rate of spontane- ous resolution in this study and those previously published are very similar.11,12 These values cor- relate with the PPV of ultrasound (all grades). Practical interpretation of the PPV is the percentage of those being identified that would have become clinically ill. The PPV of ultrasound (all grades) is 17% in this study. A higher PPV would result in treatment of fewer Regressors. While an improvement in PPV is much desired for screening programs, it should not be accepted at a significant loss of sensitivity. In the study popula- tion, thoracic ultrasound correctly identified all seven individuals that progressed to clinical disease. Sensitivity of thoracic ultrasound (all grades) is the percentage of animals that were going to develop clinical disease that were identified, 100% in this study. In fact, thoracic ultrasound (all grades) had a perfect sensitivity for each of the previous 12 years on the study property.


528 2019  Vol. 65  AAEP PROCEEDINGS


In this study, the PPV generated by using blood-


work (WBC, SAA, or fibrinogen) with all thoracic ultrasound lesions (all grades) was an improvement over that of ultrasound alone (Table 3); however, sensitivities correlating to each lab test in conjunc- tion with all grades were less than perfect. While fibrinogen did not prove to be helpful at all in the prediction of progression to clinical disease, WBC and SAA appear to be of substantial assistance es- pecially when applied to higher grade foals. Sensi- tivity of 100% was able to be achieved when WBC and SAA were evaluated at the point of larger tho- racic grades. The combination of WBC with grades 345 and SAA with grades 45 both were able to maintain 100% sensitivity while improving PPV over that of ultrasound (all grades). Although the improvements in PPV compared to ultrasound alone were not extreme, they are nonetheless significant. Decreasing unnecessary treatment by even a few animals would be beneficial. In this study, using higher cutoff values for the laboratory results did improve the PPVs even more; however, doing so sacrificed the perfect sensitivity (Table 3). Comparing the descriptive values of WBCs and


SAA in this study, perfect sensitivity was able to be achieved for a larger population of foals (grades 345) when using WBCs with ultrasound than with SAA and ultrasound (grades 45). Although SAA had a stronger PPV at grades 45 than that of WBC at the same grades, the ability to successfully apply WBC cutoffs to more foals at an additional grade is significant in practice. Ideally, a lab test would have been identified that


could have been used reliably at all grade levels. In addition to evaluating the lab values of Progres- sors versus Regressors in light of a grade cutoff, all


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