Identity testing is not usually performed in medical pathology laboratories. It is sometimes referred to as “DNA testing”, a term most frequently used in relation to criminal investigations. "DNA testing" is an unfortunate misnomer as all types of genetic analysis, whether for disease or identification or for tissue typing, involves assessment of DNA or RNA.
Identity testing focuses on the identification of an individual through the analysis of either nuclear or mitochondrial DNA extracted from some material: blood, tissue, hair, bone, etc. Any material that contains cells with nuclei can be used for nuclear DNA extraction and eventual identity testing. Mitochondrial DNA, which is “extra-nuclear,” is used when a sample is severely degraded or if only hair shafts with no attached cells are available.
Increasingly, identity testing is used to identify a suspect in a criminal investigation by comparing the DNA found at a crime scene to that of the suspected individual. If the suspected individual is convicted of the crime, his or her DNA polymorphisms are put into a data bank system that is accessible by law enforcement officials. Other uses of identity testing are to identify individuals whose identity cannot be distinguished by other means, as with decomposed bodies.
In identity testing, it is common to examine regions on the DNA that are referred to as microsatellites or minisatellites. Such regions are composed of a variable number of repeats of a set sequence of DNA. Sometimes these repeated sequences are called short tandem repeats (STRs) or variable number of tandem repeats (VNTRs). There are numerous such regions spread throughout a person's DNA, and the combination of the number of repeats in the various regions is unique to an individual. In forensics, the unique combination of repeat sequences in the various mini or microsatellites is often given the name “DNA fingerprint.”
Other types of identity testing include the determination of an individual’s parent or parents, often called “parentage testing”.