Use it or Lose it: Is expertise in some body fluid examinations being lost?
As body fluid examinations have become heavily focused on the ability to obtain a DNA profile, the expertise in analysis and interpretation of tests for some of the more rarely encountered body fluids, including urine and faeces, has become limited. Some of the main forensic providers no longer offer this testing under their UKAS Accreditation. In a case, reviewed by Forensic Context, in which there was an allegation of the offender urinating onto the clothing of the complainant, the lack of any testing for urine was questioned by the defence and clarity sought as to whether testing was possible or simply not offered by the prosecution provider.
Testing for urine
There are a number of physical and chemical tests which can be used to attempt to identify the presence of urine staining. However, in general it is very difficult to detect urine where stains are not visible and its likely location is unknown. Urine stains are known to fluoresce under ultraviolet (UV) light. Therefore the examination of an item under UV light may reveal staining which could potentially be urine. The characteristic smell of urine may not be detected until staining is damped and/or warmed. There are several chemical tests which can be employed most commonly the DMAC or RSIDTM tests, which vary in their sensitivity and specificity. However, these tests are generally used when the location of potential urine staining has been identified either because staining is visible, or when the position of staining can be predicted from the account provided. They are not used to search an item to locate staining of interest.
None of the tests available confirm the presence of urine unequivocally. In addition, other body fluids (such as semen, sweat and vaginal secretions) can give false positive reactions. An expert will therefore use the results of the examinations/tests to provide an opinion with respect to whether or not urine is, or may be, present.
The absence of visible staining, characteristic urine smell or positive reactions from the chemical tests may not necessarily mean that urine is not present, not least because any staining may be too weak/dilute. The amount a person has drunk will affect the concentration of their urine. Other body fluid examinations may also affect the ability to detect any urine present and the sensitivity of the chemical tests may decline with the age of the stain. Again, an expert can consider the results and the specific contextual case information to provide an opinion with respect to whether or not urine is absent.
DNA profiling of urine stains
Cellular material which is shed from the lining of the urinary tract is likely to be present in urine in small amounts. DNA in these cells may be detectable with current DNA profiling technologies which are now very sensitive. Published research indicates that, in theory, it should be possible to obtain a DNA profile from urine staining. However, the result is likely to be weak at best which may result in difficulties attributing any DNA profile specifically to urine.
Attribution of DNA profile to urine
In itself a DNA profile provides no information to identify the biological material giving the profile. However, when a profile is obtained from a sample in which a body fluid has been detected, the expert is able to give an opinion regarding whether or not the profile can be attributed to the detected body fluid. For example, when a weak blood, semen or saliva stain is present it is possible that the DNA within it gives no result but underlying DNA from other cells has been detected. In this situation it would be wrong to state that because the DNA matches an individual, the blood, semen or saliva came from them – for example it could be that it their DNA is present because they have had contact with the item not because their body fluid is on it. Because urine has low levels of cellular material within it, the profile obtained is likely to be relatively weak and therefore may be due to the presence of other sources of DNA, so it will be very difficult to attribute a DNA profile specifically to urine.
Back to the case example mentioned at the beginning of this post – the complainant’s upper clothing had been submitted to the forensic provider. An examination for semen had been requested as the complainant had alleged that the offender had forced her to give him oral sex. Areas of potential semen staining were located on the upper front of the complainant’s top, but the presence of semen could not be confirmed. DNA profiling of these areas also gave no DNA which could be attributed to the defendant. The defence team had been told by the prosecution that testing for urine was ‘not possible’ but they had not been provided with any reasons or explanation for this view.
We reviewed the work that had been carried out and it became apparent that the forensic provider had not been given any information regarding the urination allegation with the initial laboratory submission as the complainant’s account was unclear at this time. Therefore, they had set their examination strategy without any consideration of examining the upper clothing for urine. Unfortunately, the examinations for semen had compromised any subsequent urine examination. We were able to provide a report for the defence team detailing the potential outcomes of urine testing, the likely interpretation of both positive and negative test results in the case context, and the limitations of any urine testing due to the work which had already carried out. This case highlights the necessity for the scientist to have all of the relevant information when setting the initial examination strategy.
Forensic Context’s scientists have wide experience of the range of analytical tests used for various body fluids. If you would like assistance in any of your cases, please contact us to discuss your case with one of our experts for an initial view.