A cheek swab is a routine medical procedure that is done to collect cells for laboratory examination. A doctor, nurse, or other medical technician administers this test simply by rolling a cotton-tipped wooden speculum over the inside of a person's cheek and then sealing this sample in a sterile container for safe transport to a lab. A common purpose of a cheek swab is deoxyribonucleic acid (DNA) analysis for crime scene investigations or genealogy studies. Doctors sometimes use a cheek swab to help detect certain types of cancer, and one of these cell tests is also sometimes used to check for evidence of recent illegal drug use. Getting this kind of swab test for substance abuse is generally done as a condition of employment or to ensure routine compliance with terms of probation for drug-related criminal offenses.
A DNA swab is often performed when necessary to determine a person's paternity; a cellular match with a possible father indicates a positive test result. Some people conducting studies of their anthropological lineage sometimes use cheek swabs to match their mitochondrial DNA to that of possible ancestors that has already been collected and stored in laboratories. These kinds of tests are frequently able to trace direct parental lineage across many years as well as continental migration patterns.
Forensics investigators often rely on a cheek swab to identify criminal perpetrators out of a group of likely suspects for a given case. Matches of trace DNA from crime scenes to the cheek swab results are usually reliable forms of evidence that can be admitted in court. An additional advantage of a swab test is that it often takes a shorter amount of time to receive the results than is the case with a similar type of blood test for DNA.
Another useful purpose of a cheek swab test is the early detection of lung cancer. The cells taken from a cancer patient's swab are actually altered in minute ways that many microscopes are not able to detect until a later point in the disease's progression. This phenomenon is known as a field effect, which indicates that cell changes are detectable in the mouth at a distance from the site of the cancerous growths in the lungs. Cheek swabs for cancer detection are also frequently used for tests with specialized optical equipment that checks for different patterns in the light reflections of cancerous cells versus healthy cells.