Handling of blood sample

Its called chain of custody and the answer is it generally can be proven my documentation however the shipping and handling and length of time between the draw and the blood tests are critical issues for accuracy

Chain of custody is what you are referring to. Generally, a local lab is used, and a technician or representative of the lab will collect the samples from the law enforcement agency directly. While shipping a blood sample via US mail might not be illegal, it can create the potential for problems which might benefit a defendant's case.

It may be a "legal" method to transport the blood sample, but as Mr. Hernandez points out, it might create chain of custody problems for the prosecutor if it turns out that the sample was not refrigerated for a certain period of time, thus creating a chance for fermentation or other contamination of the sample. Speak with an attorney for specific guidance in how to attack this potential issue.

Normally, law enforcement has a storage vault they keep samples in that lab personnel then picks them up from. However, if Chain of Custody is what you meant by "change of command", your attorney could simply subpoena it.

It is the responsibility of the prosecution to prove the chain of custody with regard to evidence (including blood samples). When they fail to follow protocol it provides and opportunity for defense to call into question the accuracy of the evidence and may lead to an acquittal. So long as CHP is following their procedures, the shipping of the sample is legal. However, it may raise questions as to the temperature, how long the sample sat before being tested, whether it was contaminated etc. You really need to have a good criminal defense attorney.