Hormones are found in a variety of biological fluids including saliva, cerebral spinal fluid, blood, serum and urine. Saliva and serum are the most popular forms for testing, although they represent different forms of hormones. Saliva represents the free (unbound) or biologically active portion of hormones while serum measures total levels of bound and unbound hormones.
There are many arguments why a practitioner would choose to measure serum or salivary levels of hormones over the other, but validity of testing should not be one of them. Literature has explored the significant correlation between serum and saliva for assessing hormone levels.
- Worthman et al (1990) measured salivary and serum estradiol levels in women under ovulation-inducing therapy. They found that free levels of estradiol in saliva and serum are strongly correlated (p<0.0001).
De Boever (1986) found that there is a correlation between paired saliva and serum progesterone in healthy women during the regular menstrual cycle (p<0.001) (Figure 2).
- Researchers found that salivary testosterone levels positively correlated with free serum testosterone in eugonadic men (r=0.92, p=0.0001) (Arregger 2007). The results showed that salivary testing can be used as a noninvasive approach to the diagnosis of male androgen deficiency.
While the correlation between serum and salivary levels is strong, sex hormone binding globulin (SHBG) levels can affect the ratio between free and bound hormone levels. It is not possible to accurately compare saliva and serum hormone levels in a patient with either low or high SHBG levels. More information on the correlation and serum and salivary hormone levels can be found in Module 5 of the Reproductive Endocrinology Curriculum, which is available here (log in required).