I wrote an article several years ago in the Alternative Medicine Review outlining how common laboratory biomarkers (tests) have been found to be correlated in some manner or another with excessive bone loss and/or a heightened risk for breaking a bone. These tests can therefore be used, not as direct indicators of bone density or strength, but as indirect “indicators” or surrogates, of bone health and fracture risk. The use of therapeutic targets for reducing fracture risk is one of the most important things you and your doctor can do in managing your treatment of osteoporosis.

This is how it works: A lab test is performed and the results come back as abnormal. The physician attempts to normalize the result (through diet, changes to life-style, supplementation, exercise and/or medication) and then, through subsequent serial testing, determines success or failure.The doctor’s ability to design and fine tune therapeutic protocol is enhanced. Using lab tests in this manner as a way to determine success or failure of therapy is far superior to waiting the recommended two years between bone density evaluations. In addition, when measuring bone density, only one aspect (quantity) of bone is assessed. The assessment of changes in bone quality, as can be inferred through lab testing, provides intermediate indicators of bone health to help guide therapy.
Cortisol can be one such marker. Cortisol is a hormone produced by the adrenal glands in response to stress. Measuring cortisol through saliva is simple, non-invasive, and accurately reflects the amount of unbound cortisol levels in blood. This is important because elevated cortisol levels, while often asymptomatic*, increase a person’s risk for fracture by silently eroding away bone density and strength – reducing bone quantity and quality. It is estimated that approximately 1 to 10% of people with osteoporosis have elevated levels of cortisol. 
In one study, Morelli et al. (2011) found that in patients who have an excess production of cortisol (a condition called subclinical hypercortisolism or SH) who had normal or osteopenic (not osteoporotic) bone density, 48% sustained fractures compared to 13% in the non-SH group. In a second study conducted by researchers at the University of Milan, Italy, 102 patients with adrenal incidentalomas** (with and without subclinical hypercortisolism) were assessed for bone quality and fracture risk. The authors concluded “that in patients with subtle cortisol excess, TBS (trabecular bone score) [a method of determining bone quality and strength] is reduced and correlates with the number and severity of vertebral fractures and with the degree of cortisol excess.
In the cortisol example, a simple saliva lab test may provide important clues to the causes of your bone loss. Any abnormal test results provide you and your doctor with therapeutic targets for improvement. On subsequent testing, positive changes will indicate that the therapy you and your doctor have initiated are making an impact—and that your health, and that of your bones, are improving. 
*       Symptoms when displayed include central weight gain, excess sweating, thinning of skin and bruising, high blood pressure, elevated blood glucose, muscle weakness, irritability, etc.
**    Incidentalomas are adrenal gland tumors that have been found incidentally while performing another,
       unrelated, diagnostic procedure. Approximately 30% of patients with subclinical hypercortisolism are found
       to have adrenal masses.
Morelli et al. 2011. Risk of new vertebral fractures in patients with adrenal incidenaloma with and without subclinical hypercortisolism: a multicenter longitudinal study. Journal of Bone and Mineral Research. 26:1816-1821.
Eller-Vainicher et al. 2012. Bone quality, as measured by Trabecular Bone Score (TBS), in patients with adrenal incidentalomas with and without subclinical hypercortisolism. Journal of Bone and Mineral Research. doi 10.1002/jbmr.1648.