I hope you have good luck getting your medical records. Reading through mine helped me process what had happened when my daughter was born. It sounds like you were very sick, and you had almost every scary red-flag PE/HELLP symptom in the book. It is impossible to say whether your doctors made a mistake sending you home because this disease can move so quickly. While it is possible that they did, it is also possible that you got much sicker in hours. Many of us would probably be more comfortable being monitored in the hospital when things start to go bad, but that isn't always possible or prudent. I am glad that you and your son are ok now.
Many women have elevated uric acid levels when they develop pre-e/HELLP. I don't think that it is considered a "hard indicator" of HELLP, but many doctors do monitor it. They are primarily looking for hemolysis, low platelets, and elevated liver enzymes. I think that my uric acid was also elevated, but pretty much all of my values were off by the time I actually went in for blood work.
Daughter born April 2009 at 35 weeks due to Class 1 HELLP