What Can Taking Swabs of Your Cheek Identify?

A cheek or buccal swab refers both to the tool used for the procedure and to the sample collected. Swabbing involves the use of specialized applicators tipped on one end with cotton, polyester or foam, with a wooden or plastic handle measuring at least 6 inches. Taking a swab is a noninvasive, painless procedure in which the applicator is rubbed against the inside of the cheek, where it picks up epithelial cells and saliva.

DNA Profile and Genetic Disorders

• Cheek swabs are widely used in crime labs and medical laboratories as sources of DNA for profiling and diagnostic purposes. Crime labs use swabs as tools for identifying individuals and as references to which unknown samples can be compared or matched. Medical laboratories, on the other hand, gather samples with swabs to pinpoint aberrations in chromosomes, proteins or DNA to help them identify a patient's specific disorder. While blood, hair, skin or amniotic fluid can be used for either purpose, cheek swabs offer the best balance between noninvasiveness and accuracy.

Tissue Compatibility

• A cheek swab can also determine a match between an organ donor and a patient. Tissue typing is done through a process called the "human leukocyte antigen" (HLA) test. A technician uses cheek swabs of potential donors to see if their white blood cell antigens match those of the patient. This process guards against tissue rejection -- the result of the recipient's body recognizing antigens on the donor's tissue as foreign. HLA tests are most commonly used for heart, liver, kidney, pancreas and bone marrow transplants, where a greater number of identical HLA antigens means a bigger probability of a successful transplant.

Parentage

• A cheek swab can also provide information for paternity tests, again by comparing HLA antigens. A child's HLA antigens must be attributed to either the mother or the father. A mismatch means the exclusion of either as a parent of the child. Cheek swabs provide just as much accuracy as a blood test and have the additional advantages of their being noninvasive and completely unaffected by recent blood transfusions and bone marrow transplants.

Drug Use

• Finally, cheek swabs are used for saliva drug testing to determine whether the person in question has recently taken illicit drugs. Rather than rubbing the swab against the inside of the subject's cheek, the person collecting the sample allows the swab to get saturated with saliva. Saliva drug tests can easily detect the presence of marijuana, heroin, amphetamines, cocaine and THC, and offer an easy, cheat-proof means of gathering samples; however, cheek swabs for drug tests are limited by time and cannot be used reliably after about 12 hours.