I would contact a local attorney for advice. Typically, most DUI attorneys hire their own expert to challenge blood evidence. There are a few national manufactures that produce the tubes wherein blood is stored for testing. These tubes have preservatives that claim to slow the process of contamination of the blood. However, there are always issues to challenge. Good luck.
If the proper amount of preservative is present and the sample tube is undamaged, it can remain usable for years. Five months should be no problem.
Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this site, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.