Is saliva sampling a viable non-invasive option?
Using saliva as a sample for analysing hormone levels was first identified in the late 1960s and over time this has become more and more popular. It has definitely become a viable alternative to blood and urine sampling, with some instances it is now the preferred choice.
Benefits of using saliva samples include:
. Simple collection method that is not invasive and stress free.
. No special equipment or highly trained personnel required.
. It is easy to store, transport and stable at room temperature.
. Testing can be done on either men or women.
. Number of saliva samples can be easily taken throughout the day or over a longer period of time without having too much stress or discomfort imposed on the donor.
Saliva is also a well known fluid that can offer “real-time” profiles which indicate the well-being and health of an individual at the moment of collection. This is only possible because the salivary gland is an exocrine gland. This important property is really useful when looking at hormones which are found to be secreted at many different points throughout the day, for example; melatonin saliva and cortisol saliva. By collecting multiple saliva samples of these compounds during the day or even night will allow one to obtain a representative picture of normal versus any deviation of the “real- time” cyclical pattern. Whilst theoretically this can be done with a serum or urine sample test, it would however be stressful, uncomfortable and logistically cumbersome.
One major benefit of using salivary samples is its ability to detect the bio-available or free portions of the total hormone at a given time point. The free fraction represents the amount of hormone that is not bound by binding proteins in blood. Has many steroid hormones are found to be bound to their respective carrier protein; for example: globulin, albumin and cortisol binding protein then it is only the free or unbound steroids which are available for cells to uptake. Hence, it is not the bound/total hormones levels which are measured with serum samples but the free hormones that is measured in saliva which are best reflecting an individual patient hormone related symptoms. This extremely important property allows researchers to predict an estimation of how much hormone is free in the blood which can then enter into tissues.
Furthermore, saliva test assay are effective at monitoring the concentrations of free hormones in addition to their utilisation and absorption. There have been research studies that have confirmed the detection of progesterone saliva is actually also being absorbed, even though there is no difference in serum progesterone. This has led to the belief that saliva tests can have an influence on supplementation dosages and identify if bio-identical hormone therapies are being absorbed. However, as this is not identical to specific tissue levels it can be clinically misleading if one solely relies on salivary hormone tests. Therefore it is recommended to carry out other tests and experiments to verify the salivary results.
Limitations of using saliva sample include:
. Restricted to analysing steroid hormone only.
. Saliva can be easily contaminated by; bleeding gums, make-up on lips and hands, mouth infection (open ulceration) and food.
. Results can also be affected by everyday infections such as; flu, colds, sinus congestions and certain allergies.
. There is a lack of familiarity.
. Salivary assay are not FDA approved.
One major disadvantage lies when collecting multiple samples from older people since many of them are on prescription medicine which causes them to have a dry mouth due to the lack of saliva. A similar situation is also found in individuals that have certain auto-immune diseases that lead to dry mouth and eyes.
Another significant limitation for salivary diagnostic studies is the fact that the hormone concentrations present in saliva when compared to the blood are considerably lower. It can be anything from 200 to even 5,000 times lower when compared to the levels that are present in the blood. This is because hormones pass from the blood to the saliva by ultra-filtration, and need to be very small for this process to be efficient. Since the hormone concentrations levels are so tiny, this results in the reference range for saliva being difficult to interpret for any clinical significance.
Finally, saliva results obtained can be found to be much higher than expected in some cases due to contamination by blood. This is mainly in the form of bleeding gums and in some cases it is not visible. The concentration of hormone present in this situation is found to be higher because added blood hormones are now being introduced to the saliva sample. These results need to be discarded and repeated, since there is no way one can make adjustments for this kind of contamination.
When comparing methods that are available for serum against saliva sampling, we find that there are pros and cons for each of them.
Published data has shown that in certain cases saliva sampling is more accurate when compared to serum methods, for example; testosterone bioavailability (at low levels only), estrogen in men and testosterone in children and women.
However, the saliva methods that are available are restricted to measuring steroid hormones only. Many other peptide hormones (for example; thyroid and growth hormone) are not available.
Saliva testing is convenient, easy and multiple samples can be taken. It is more precise in measuring very low levels of free hormones, thus making it important in the diagnosis, planning or maintaining accurate treatments for healthy living and well-being.