When an expiration date has passed, look for the following problems:
1. A bad seal on the vacutainer, which is impossible to detect after the test, because it has been opened.
2. Improper amount of sodium flouride in the vial. Since vials are routinely not refrigerated prior to their delivery to the crime lab, the proper amount of sodium flouride is critical. Either too much or too little can lead to a false high test result. Unless there is enough sodium flouride in the vial, the organisms that may be in your client's blood will grow. One such organism is the ubiquitous candida albicans, which is is a yeastlike organism that is resistant to sodium floride. In the presence of glucose and warmth, it will excrete ethanol via fermentation.
3. Improper amount of potassium oxalate. With too little in the tube, microclotting may result, and this will yield a false result.
And There's More.
As you might expect, if the seal has been compromised, ambient room air may also be drawn into the collection tube. Becton-Dickinson only checks one in every 4000 tubes for the proper amounts of preservative and anti-coagulant, which simply compounds the chances of an analytical error when the expiration has passed.