Whether the police may see your medical records depends on 1) whether you gave them permission, and 2) whether they have probable cause to get a warrant for those records.
Understanding Your Right to Privacy
There are many laws in place within the US that protect your right to privacy, especially when it comes to medical records and law enforcement:
When Police Can See Your Medical Records
While your right to privacy and your right to be free from search and seizure do provide you with protection, that protection is not absolute. If you give the police permission to see your records, then they may use anything contained within those records as evidence against you.
In addition, if the police have probable cause to believe you were under the influence of alcohol or any other illegal substance at the time of the accident, they may take that information to a judge who can sign a warrant to obtain your records. If the warrant permits the police to review the blood test from the hospital, then the blood test results may be used against you in court.
Getting Help
If you were driving under the influence of alcohol and caused an accident, you could find yourself in some very serious legal trouble. If you believe that your private medical records or blood tests may contain evidence against you (i.e. - indicate you were intoxicated), then you should contact an experienced attorney as soon as possible. The earlier you contact a lawyer, the better your chances are of avoiding arrest and/or successfully defending yourself in court.