Emedinews:Insights on Medicolegal Issues:Is Touch DNA test different from a DNA test?

Human being shed tens of thousands of skin cells each day, and these cells are transferred to every surface with which human skin comes into contact.

• Both are the same. But, a DNA test is done using visible biological samples like blood, saliva, semen etc. While, samples for touch DNA are usually not visible and since they are often deposited in smaller amounts than the DNA found in bloodstains or other body fluids, it is more difficult to obtain DNA profiles from these samples. This means that low copy DNA profiling allows a very small amount of DNA to be analyzed, from as little as 10 to 30 cells. DNA in skin cells that are left at a crime scene may be sampled from a variety of items including gun grips, steering wheels, eating utensils, luggage handles, and clothing
• Touch DNA samples are also processed exactly the same way as blood, semen, and saliva etc. Touch DNA analysis may be able to link the perpetrator to the crime scene, by collecting the skin cells and analyzing them.
• The key to obtaining successful Touch DNA results depends on recognizing items which may be suitable for Touch DNA analysis and using the sampling technique or collection method that will recover the highest number of skin cells.
• Locard exchange principle states that with contact between two items, there will always be an exchange. So, when a crime is committed, if the perpetrator deposits a sufficient number of skin cells on an item at the scene, and that item is collected as possible evidence.
• The techniques used are:
• Swabbing: The surface of the item is rubbed with a cotton swab to collect possible cells. This method is preferred for hard items such as glass or plastic.
• Cutting: May be used for soft items, such as clothing, in which fabric from areas of interest is cut to collect possible cells.
• In addition to the commonly used swabbing and cutting methods, the latest technologies has recently started using the "Scraping" and "Tape Lift" methods, in which the surface of soft items such as clothing are either scraped with a blade, or sampled with a small piece of tape, to collect possible cells.