My research says that it takes three negatives to consider the diagnosis negative for cryptosporidiosis. My choice would be to have three different tests done rather than the same one done three times. Example: Acid fast on the feces, and on the regurge. And an ELISA on plasma or Immunofluorescent Antibody test done on the feces.
Have you read the regurgitation protocol yet?
One other option you could try in dealing with the regurge of fuzzies is to make cuts in the skin of the fuzzy before feeding. The cuts are made over the dorsal surface (neck, shoulders, back) to avoid cutting into the abdomen and releasing the abdominal contents.
You could also try probiotics and grapefruit seed extract as a system assist. These might be a great help to your snake especially in light of the regurges that have been happening.
Try a search on this site for these to get more information. I'm pretty sure some of this information can be found in the FAQ forum.