Measurement of testosterone in the saliva is one way to directly measure free testosterone that is unbound to serum proteins. Its advantages are less apparent since the development of reliable serum assays of free testosterone.
Total serum testosterone can be misleading since much of the testosterone is bound to protein. Many diseases may affect the level of the various binding proteins so that it is difficult to interpret the significance of a total testosterone result.
The physiologically important measure is the amount of unbound ("free") testosterone that can bind to cell receptors. This is the form of testosterone in saliva.
Fraction
Total Testosterone
Bioavailable Testosterone
Free (Unbound) Testosterone
bound to sex hormone binding globulin (SHBG)
44%
No
No
bound to albumin
50%
Yes
No
bound to cortisol binding globulin (CBG)
3.5 %
No
No
unbound
2-3%
Yes
Yes
Advantages of salivary testosterone:
(1) noninvasive (of little import if other blood tests have been ordered)
(2) useful if a reliable serum free testosterone assay is not available
Limitations:
(1) reduced saliva production in severe xerostomia
(2) interference from intra-oral contaminants
(3) requires a special saliva collection device
A low salivary testosterone level can reliably identify a man with hypogonadism.
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