A cheek swab, often called a buccal swab, provides a non-invasive method for collecting biological material for DNA analysis. This procedure involves gently rubbing a sterile swab against the inner cheek to gather buccal cells, which contain an individual’s genetic blueprint. These samples are used in genetic testing, forensic science, and research. Ensuring the integrity of the DNA sample after collection is important for accurate and dependable results.
Factors Influencing Sample Integrity
The longevity of a cheek swab sample is influenced by various factors, both environmental and biological. Environmental conditions, such as temperature extremes, directly impact DNA stability. High temperatures can cause the DNA strands to break apart, leading to degradation. Freezing can preserve DNA, but repeated freeze-thaw cycles can damage it.
Humidity also plays a substantial role, as high moisture levels can accelerate DNA degradation processes and foster the growth of microorganisms. Exposure to light, especially ultraviolet (UV) radiation, can chemically alter DNA by forming damaging linkages between bases, thereby compromising its integrity.
Biological factors within or introduced to the sample also affect its viability. Microbial contamination from bacteria or fungi, naturally found in the mouth or introduced during collection, can lead to DNA degradation through enzymatic activity. Additionally, enzymes known as DNases can actively break down DNA molecules. Substances called PCR inhibitors may interfere with downstream DNA analysis techniques. The initial collection technique, including pre-collection activities like eating or drinking, or improper drying, can impact the overall quality and quantity of DNA obtained.
Proper Storage Methods
Proper storage methods are important immediately after collection to maximize sample viability. For short-term preservation, typically up to two to three weeks, storing samples at room temperature is often adequate, provided they are correctly dried. Studies indicate that human DNA yield and quality remain stable under these conditions for at least two weeks. For slightly longer periods, refrigeration at around 4°C can further slow degradation.
For long-term archiving, especially if analysis is not immediate, freezing samples at -20°C or colder is the recommended approach. This low temperature significantly halts enzymatic activity and microbial growth, preserving the DNA for extended periods, potentially months or even years. While freezing preserves DNA, repeated freeze-thaw cycles can cause damage, so minimizing these cycles is beneficial.
Humidity control and appropriate packaging are also important. After collection, allow the swab to air dry thoroughly in a breathable container, such as a paper envelope or specialized self-drying tube. This prevents moisture accumulation that can encourage bacterial growth and DNA degradation. Avoid non-breathable or certain plastic containers, as some plastics can leach substances that may interfere with DNA integrity or analysis. Some collection kits include a stabilizing reagent on the swab, which helps to lyse cells and protect the DNA by inhibiting degrading enzymes, thereby extending the sample’s shelf life.
Consequences of Sample Degradation
When a cheek swab sample degrades, it can no longer reliably serve its intended purpose, leading to negative outcomes. The most immediate consequence is the potential for inconclusive or inaccurate test results. Degraded DNA may not provide enough intact genetic material for proper analysis, making it difficult to generate a complete genetic profile or identify specific markers. This can result in partial profiles, where only some genetic information is detectable, or even false negative results if the target DNA cannot be amplified due to degradation or the presence of inhibitors.
Insufficient quantity or quality of DNA directly impacts the success of downstream laboratory procedures, such as Polymerase Chain Reaction (PCR) or sequencing. If the DNA is highly fragmented or contaminated, it becomes challenging for laboratory equipment to accurately read and interpret the genetic code. This often necessitates a re-collection of the sample, which introduces delays in obtaining results.
Beyond the time implications, re-collection can also lead to additional costs for new collection kits, shipping, and repeated laboratory processing. This can be a burden in research studies, clinical diagnostics, or forensic investigations where timely and accurate results are important. Ultimately, the degradation of a cheek swab sample compromises the reliability of genetic information, undermining the entire purpose of the collection.