How do we collect DNA samples?

Written by: Nermin Đuzić, M.Sc. in Genetics, Content Specialist

Recently, we have been writing about genetic tests, their importance, and their applications. Although explained as a simple process of looking for changes within your genetic material,  genetic testing is a complex and step-wise process, from sampling over DNA extraction and various quality checks to finally obtaining and analyzing results. We divide the whole procedure into the following steps:

• Collecting the sample
• DNA extraction
• DNA quality control, storage, and management
• Genotyping
• Obtaining  and analyzing genotyping results
• Generating report

In this article, we will explain the procedure of saliva sample collection. By definition, DNA sampling represents the method of obtaining biological material to undergo further DNA procedures and analyses (first of all DNA extraction and then using extracted DNA for ancestry or genealogy testing, paternity testing, genetic screening for diseases…). 

It is often the first and most crucial step in conducting research or performing any analysis in molecular biology. The sample collection technique mainly depends on a sampling DNA kit and typically involves samples from buccal swabs, saliva, or blood [1, 2].

How do we obtain a saliva sample?

There are several ways of collecting DNA samples, most of them being non-invasive and painless. DNA can be obtained from literally all living material: tissue, nail, blood, saliva, semen, or hair. Here we explain the procedure behind saliva sample collection, as we at BioCertica rely on it.

Saliva, also known as spit, is an extracellular fluid in the mouth produced by salivary glands. Human saliva consists of 98% of water but also contains electrolytes, mucus, white blood cells, epithelial cells., enzymes, antimicrobial agents, and lysozymes [3].

At BioCertica, the whole procedure starts when you order one of our DNA kits, and it comes to your address. Within your ordered DNA kit, you will find detailed and step-wise saliva swabbing instructions along with a sample bag. The easiest way to collect a saliva sample is to simply drool into the collection container you get within the ordered DNA test kit [4].

Below is Figure 4 with detailed instructions on sample collection. In order to ensure the DNA test integrity and quality, all stages of sample collection have to be conducted under strict protocols. After collection, samples are usually sent via couriers to the laboratory appointed for DNA testing.

What should you pay attention to before and after sample collection?

It is crucial to ensure your sample integrity and quality are maintained during the whole sampling procedure. It is essential to follow these guidelines to ensure sufficient DNA yields. Here are several notices you should remember to provide lab technicians with enough quality DNA samples for genotyping and analysis [5, 6].

1. The best practice is to collect your sample in the morning before eating or drinking anything except water. Otherwise, refrain from eating, drinking, smoking, chewing, teeth brushing at least 30 minutes before collection.
2. Do not remove the plastic film from the funnel lid that contains the clear liquid. 
3. Make sure you do not touch the tips of the funnel lid to avoid contamination. Also, do not put it on a contaminated surface. However, if you are collecting a sample from someone else, you have to be careful since you could contaminate the sample with your DNA.
4. Do your best to provide enough saliva (not including foam) to reach the “Fill to” line before you close the lid of the funnel. Let the foam settle before you close the lid or it will overflow.
5. You should not re-open the tube and add more saliva once you close the funnel.
6. Do not rest the tube on a tabletop when it is open, as it will tip over. Instead, place it upright in a glass if you need to put it down for some reason.
7. Before spitting, relax and rub your cheeks gently for 30 seconds to make enough saliva. 
8. If you find it difficult to produce enough saliva, place a very small amount of white table sugar on your tongue. 
9. Do not ingest the liquid in the funnel. Wash with water if liquid comes in contact with your eyes or skin.
10. Store your DNA in a dry and clean container. Also, DNA kits will usually contain collection envelopes or vials along with instructions for proper storage. 
11. Label the date when collecting the sample. Keep it away from moisture, chemicals, and extreme temperatures.
12. Follow the packing and shipping instructions provided within the DNA kit. 
13. Environmental conditions such as sunlight, high temperatures, moisture, and chemicals may damage samples and degrade DNA. Therefore, the best practice is to order the courier to pick up your sample on the day of collection. 

Here is a short video if you would like to see how it practically works.

What are other methods of sample collection?

As we have already explained, DNA is not solely collected from saliva. It can also be collected from many sources, including blood, buccal cells, semen,­ nails, etc.  The inner part of our mouths is rich in squamous epithelial cells. These cells are often called cheek cells, and they take approximately 5-12 days from production to detachment from the epithelial surface. Therefore, they are easy to obtain by mouth rinse or simple swab, making them the perfect tool for obtaining and analyzing an individual’s genetic makeup [7]. 

All you should do is take it out and rub it gently inside one of your cheeks for 45 seconds. Scrape vigorously, but make sure it does not hurt. Seal the vial and repeat the same with another swab and cheek. Kits often contain more than one swab if one swab does not have enough DNA or DNA quality is compromised.

Not long ago, we relied on swab samples but recently decided to replace them with saliva samples. Here are a few reasons why we have decided to shift: 

• Saliva samples provide sufficient DNA quantity and better quality for genetic testing purposes, compared to buccal swabs.
• Buccal swabs need to be processed rapidly to have an appropriate DNA yield. However, saliva samples are more user-friendly.
• Saliva samples are easier to handle and less invasive, without discomfort. Everything you should do is spit into the container [8]. 

On the other side, blood samples come in two ways: blood tubes and FTA (Finger Technology Association) cards [9, 10].  The first method is a standard collection of blood in the tube using a standard blood collection needle. 

Another method is to use FTA cards, which are chemically treated, cotton-based filter papers designed to collect, preserve, and ship biological samples like DNA. In this method, DNA is trapped and adhered to papers.

What after sample collection?

The first step is to sign up in the BioCertica mobile application. Then you should follow a sequence of steps, easy as the ABC depicted below (Figure 4).

As depicted above, after completing the sample collection, you will need to activate your test kit online at BioCertica mobile app by scanning the QR code on your camera phone. You will immediately get instructions on how to register your kit.

Upon registration, you will need to schedule a courier to pick up your samples and deliver them to the lab as soon as possible. After this, our team will reach out to you via e-mail and send you a lifestyle questionnaire. 

Figure 5: BioCertica DNA saliva sample

Finally, you will get results within 4 to 6 weeks after sample collection. Of course, we will notify you once your results are ready! Do not wait! Order your kit now here! 

References

1. Mullegama, S. V., Alberti, M. O., Au, C., Li, Y., Toy, T., Tomasian, V., & Xian, R. R. (2019). Nucleic acid extraction from human biological samples. Biobanking, 359-383.
2. National Research Council. (1998). Evaluating human genetic diversity.
3. Young, J. A., & Schneyer, C. A. (1981). Composition of saliva in Mammalia. Australian Journal of Experimental Biology and Medical Science, 59(1), 1-53.
4. Granger, D. A., & Taylor, M. K. (Eds.). (2020). Salivary bioscience: foundations of interdisciplinary saliva research and applications. Springer Nature.
5. Butler, J. M. (2010). Chapter 4—sample collection, storage, and characterization. Fundamentals of forensic DNA typing, 1st edn. Academic Press, San Diego, 79-97.
6. Center for Birth Defects Research and Prevention (2013). How to collect saliva (spit) samples for parents? Retrieved from: draft_salivainstructionsparent_engtest.pdf (cdc.gov)
7. Lee, E. J., Patten, G. S., Burnard, S. L., & McMURCHIE, E. J. (1994). Osmotic and other properties of isolated human cheek epithelial cells. American Journal of Physiology-Cell Physiology, 267(1), C75-C83.
8. Saliva vs swab test - what's the difference? (2021). Retrieved from https://www.testingforall.org/saliva-vs-swab-test-whats-the-difference/ 
9. Guha, P., Das, A., Dutta, S., & Chaudhuri, T. K. (2018). A rapid and efficient DNA extraction protocol from fresh and frozen human blood samples. Journal of clinical laboratory analysis, 32(1), e22181.
10. da Cunha Santos, G. (2018). FTA cards for preservation of nucleic acids for molecular assays: a review on the use of cytologic/tissue samples. Archives of pathology & laboratory medicine, 142(3), 308-312.