Estrogen is needed to stimulate the reproductive tissues, and progesterone is needed to help balance and slow down the rate of cell growth stimulated by estrogen. Saliva is good for testing steroid hormones because it's representative of the bioavailability in the body. When the hormones are produced and released into the bloodstream, over 95 percent of them are bound by proteins, lead-binding proteins. Hormones in saliva are stable at room temperature for many days. This significantly brings down the cost of testing.
Doctors are more familiar with blood testing.
In time, as they familiarize themselves with saliva testing, I do feel this will change. Don't use transdermal hormone creams on your face the day before you collect your saliva, it may contaminate the saliva specimen if you have hormones on your lips when you spit into the tube. When hormones are applied to the skin, we see very significant increases in salivary levels of that hormone, but often we see very little change in the serum level. Serum testing is a valid way to test hormones if they are produced within the body endogenously, or if you were taking hormones orally. We believe the reason for this is that when hormones enter through the skin and enter the bloodstream, they're carried by red blood cells to target sites where they're delivered.