Direct-to-Consumer Genetic Testing: Accuracy, Privacy, Limitations

Over 40 Million People Have Taken a Consumer DNA Test — and the Data Question Is Only Getting Larger

MIT Technology Review estimated in 2019 that more than 26 million people had taken at-home DNA tests from the major consumer genetics companies; by 2023, estimates exceeded 40 million globally across the major platforms. 23andMe (founded 2006) and AncestryDNA (launched 2012) collectively hold the largest databases, enabling ancestry matching and genetic research at unprecedented scale. These tests democratize access to genetic information, but what they can and cannot reveal is frequently misunderstood — by consumers, by media, and sometimes by the companies themselves.

Direct-to-consumer (DTC) genetic tests use saliva samples mailed to a laboratory, where DNA is extracted and analyzed using genotyping arrays that read specific positions (variants) in the genome. Unlike clinical whole-genome or whole-exome sequencing, which reads every nucleotide, DTC tests examine a curated set of 600,000 to 900,000 single nucleotide polymorphisms (SNPs) — about 0.03% of the roughly 3 billion base pairs in the human genome.

What These Tests Can and Cannot Tell You

The distinction matters.

In 2019, 23andMe became the first DTC company to receive FDA authorization to report genetic health risk results for 10 conditions including Parkinson's disease, late-onset Alzheimer's disease (APOE variants), hereditary thrombophilia, and others. However, FDA authorization applies to the specific variants tested and the specific way results are communicated — it is not a certification that the full spectrum of disease variants is captured.

Accuracy of the Tests Themselves

The genotyping technology is highly accurate for the variants it tests. Illumina and Affymetrix genotyping arrays used by major DTC companies have per-call accuracy rates of 99.9% or higher for the SNPs included in the array. Reproducibility — getting the same result from the same sample on repeat testing — is similarly high.

The accuracy questions arise in interpretation, not in the raw genotyping:

• A variant negative result on a DTC array means only that the specific positions tested are not flagged — not that no disease-associated variants exist elsewhere in the genome
• Ancestry estimates are statistical inferences based on comparison to reference populations that are themselves samples of current-day populations, not ancient populations. Estimates are regularly revised as reference panels are updated, sometimes substantially
• 23andMe has disclosed that some results carry genotyping error rates above 10% for specific variants, and the company has corrected ancestry composition estimates multiple times since 2015

Privacy and Data Ownership

Genetic data is uniquely sensitive. Privacy implications are real and long-term.

The key question customers rarely focus on: who owns the data, and where does it go?

• 23andMe's terms of service (as of 2023) state that customers retain ownership of their genetic information, but grant the company a license to use de-identified data for research and commercial purposes unless customers opt out
• 23andMe licensed genetic data to GlaxoSmithKline (GSK) for drug discovery in a $300 million deal announced in 2018; GSK gained exclusive rights to use the database for four years
• AncestryDNA has similar opt-in research participation provisions; Ancestry has partnered with CALICO (Alphabet's life extension company) and others
• Law enforcement access: consumer genetic databases have been used in criminal investigations through "genetic genealogy" — comparing crime scene DNA against uploaded profiles in GEDmatch (a third-party database where users can upload raw DNA). This technique helped identify the Golden State Killer in 2018. The legality and ethics of law enforcement access to these databases remain actively debated

When Clinical Genetic Testing Is Needed Instead

DTC tests are not substitutes for clinical genetic testing ordered by a physician or genetic counselor. Several situations call for clinical testing:

• Strong family history of hereditary cancer (BRCA mutations, Lynch syndrome, BRCA2)
• Personal or family history of hereditary cardiac conditions (Long QT syndrome, hypertrophic cardiomyopathy)
• Pregnancy or family planning with concern about heritable conditions
• Interpreting a concerning DTC result — a genetic counselor (board-certified through ABGC) provides context that DTC platforms cannot

The National Society of Genetic Counselors maintains a searchable directory of certified counselors at nsgc.org. Clinical testing is typically covered by insurance when medically indicated, unlike DTC tests, which are paid out of pocket at $79–$200.