Poor Casper, not what I wanted to hear. Doesnt help his case that colic can cause laminitis too so he's had a double whammy.
The blood tests when they are in pain in early stages more likely give a high false positive than a negative as all the bodies natural responses to stress and pain go on hyperdrive
Has the vet considered maybe kidney or liver disease as a cause?
I feel so sorry for you. Hope things improve