There are a couple of different types of blood tests but the most common is the RAST test which measures the amount of the IgE antibodies in your blood for a specific allergy trigger. The higher the IgE reaction, the more allergic you are, but the different levels are not a perfect measure of the potential allergic reaction because different allergens cause the body to react differently.
The normal levels are 0, meaning you're not allergic to a particular trigger.
The 6.6 means that you're having an allergic reaction to something and depending on how the test was run, they may be able to tell you what you're reacting to, but the severity of your allergy depenRAB on the specific allergen that's causing your reaction.