| Forensic testing for the presence of saliva is by far the most problematic of the forensic tests available. |
Understanding Saliva Testing in Forensic Investigations
Have you ever seen the following in a forensic statement or report?
“Possible saliva was detected”
“A test for amylase was positive”
This means only a presumptive or screening test has been performed, which generated a positive reaction. More often than not, there is no further information about these tests included in the report.
These statements do not mean that saliva has been detected. Furthermore, even the tests used to confirm the presence of saliva also react to other biological fluids. This means there is no confirmatory test for the presence of saliva (with the exception of mRNA testing, which is not currently available in Australia).
How Does Saliva Testing Work?
Testing for the presence of saliva relies on the presence of alpha amylase. This enzyme is present in high levels in saliva, but it is also found in other biological fluids.
For the Scientifically Minded: The Reaction Process
One of the reactions used in testing works as follows:
starch-blue dye ------> maltose (broken down starch) + blue dye
(enzyme)
This is known as an enzymatic reaction, as it relies on an enzyme present in the material to cause a reaction. This reaction generally results in a colour change. In relation to saliva testing, this enzyme is alpha amylase. You may have seen this through the use of Phadebas Press Test or RSID® Saliva tests.
Limitations of Saliva Tests
When it comes to these saliva tests, they will also react to other biological substances such as:
- Urine
- Sweat
- Breast milk
- Faeces
What Does a Positive Result Actually Mean?
Unfortunately, at the current time, there is no readily available test for the confirmation of the presence of saliva.
Furthermore, additional caution needs to be applied when it comes to the DNA results. It may not be appropriate to assume any DNA profile detected has been derived from saliva.
As lawyers, it is not appropriate to assume a biological fluid has been detected based on testing for the presence of saliva.
It is imperative to find out the limitations of this testing to prevent misleading evidence from being presented in your matter.
Presenting the Limitations of This Evidence in Court
The limitations of these tests are frequently absent from forensic reports and statements. Their absence can allow undue weight to be applied to the testing.
It is imperative to reveal these limitations to the court to prevent an over-evaluation of the evidence. IFS stands ready to help pinpoint these limitations, ensuring your case evidence receives fair and impartial evaluation.
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An Expert Team Lead by Jae Gerhard
Jae Gerhard is a Forensic DNA Expert and the Principal Forensic Scientist at Independent Forensic Services, bringing over two decades of frontline experience in forensic biology. She has worked on some of Australia’s most complex and high‑profile cases with the Australian Federal Police and New South Wales Police, as well as international disaster victim identification operations in Bali and Thailand.
Specialising in DNA analysis, STRmix™, biological fluid examination, and bloodstain pattern interpretation, Jae now works independently with criminal defence teams to review and challenge forensic evidence. Her mission is simple: to ensure the science presented in court is accurate, balanced, and truly understood.