Hello clauee,
If you wish to learn more about interpreting lab values check out:
https://horseadvice.com/horse-equine/reference-material/equine-vital-signs-and-laboratory-values/
If you wish more on diagnosis fever of unknow origin, and this would include poor doing of unknown cause check out:
https://horseadvice.com/horse-equine/diseases/fever-of-unknown-origin/
More specifically I would suggest considering running some of the more recent tests for inflammation like Serum Amalpoid A. These tests appear to be more sensitive to inflammation, response to treatment, and even have some differential ability as to the type of inflammation. For more on this check out:
https://horseadvice.com/equine-horse/equine-inflammatory-markers-serum-amyloid-a/