Saturday, March 10, 2018

Spit or Swab?

Most of us who have done DNA testing have anecdotal impressions about the success of "spit tests" and "swab tests" for collecting DNA samples. Some of us may still have skepticism about whether a little saliva can provide accurate scientific results. On this later question, I was reassured shortly after we moved to Nashville in 2012. In late 2009 my wife and I had been beta testers for 23andMe when the company was expanding from health related testing to ancestry testing. As a result we both had pre-FDA intervention reports on multiple potential health conditions and drug interactions.

Although I wanted to believe the results, I was born in Missouri -- the Show Me state. Therefore, I had a bit of residual skepticism. Shortly after we arrived in Nashville, we enrolled in Vanderbilt University Medical Center's PREDICT program which aimed at matching drug reaction information with patients' electronic medical records. For this program blood was drawn in a clinical setting and was processed in the Medical Center's labs. On a half dozen comparable tests, both my wife and I got results and interpretations from Vanderbilt that validated those we have previously received based on 23andMe's spit tests. My wife was flagged for statins and I was identified as a faster than average metabolizer of certain blood thinners by both our spit tests and our blood tests. Saliva DNA tests seemed to work just fine.  

However, the question of whether spit tests or swab tests were more likely to get usable results in the lab still remained. My wife sometimes says that her family has a "no spit" gene. It took her three tries to produce a usable sample for Ancestry. It took her sister two tries at Ancestry. Their brother was never successful in producing a readable sample for 23andMe. After two tries the company refunded his money. 

I just retested a grandson a spit test for 23andMe and that result is still pending. The grandson is not biologically related to my wife's family. 

All four of the above family members have passed swab tests on the first try with MyHeritage or FTDNA. Most of you know that samples sent to these two companies are processed through the same lab in Houston.

The Poll:

How unusual is my wife's family? Maybe I should rephrase that. How unusual is their DNA testing success? To cast a wider net to collect some data I posted a poll this week on the "Genetic Genealogy Tips and Techniques" Facebook page which claims more than 36,000 members. For a variety of reasons this turned out to be a "quick and dirty" data collection survey. I was not clever enough to bend Facebook's poll instrument to allow responders to easily enter multiple results when multiple family members had been tested. All the data is self reported from customers. I tried to enter data customers provided in comments. My quick and unscientific poll ended up with 1.333 usable testing experiences.


While testing companies will claim a higher success rate than is shown in my results, I would welcome their data to prove it. Intuitively, these data seem to reflect what many of us experience. This is not intended to be the definitive final word on this question. What do you think?

I'd love to have more data. 



  1. Isn't this data skewed because the total number of tests performed by Ancestry and 23andMe far exceeds the number performed by FTDNA and MyHeritage?

    1. Hi Doris, That is the reason why I gave the percentages of successful tests. Just above 90% for spit and about 96% for swab.

  2. Very interesting. I have found that spit tests are difficult for us "oldies." Hope you have more data coming out on this topic.