There is indeed a blood test to see if you have been exposed to the varicella (chicken pox) virus. In most people this blood test is not necessary as it is safe to give the varicella vaccine to people already immune to chicken pox. However, in certain instances, a the test is necessary such as pregnant women who either lack documentation of vaccination or don’t have a clinical diagnosis of varicella. This way, immunity to varicella can be verified.
If a pregnant women is not immune to varicella, they should avoid contact with anyone suspected of having chicken pox. In addition, vaccination should be given immediately post partum as it is not safe to vaccinate pregnant women against chicken pox.