When patients ask about genetic testing, one of the first practical questions is: how is the sample collected? The answer depends on what is being tested — and understanding the difference matters more than most people realize.

The Two Main Collection Methods

Cheek (Buccal) Swab

A buccal swab collects cells from the lining of the cheek. The process is non-invasive, painless, and can be done at home or in the office. The swab is stable at room temperature, making it easy to ship to a laboratory.

For most genetic testing — including whole genome sequencing, hereditary cancer panels, pharmacogenomics, and carrier screening — a cheek swab provides DNA that is essentially equivalent to blood. Genotyping accuracy from buccal DNA exceeds 99.99%.

Pros of cheek swabs:

• Non-invasive and painless
• Easy to collect at home
• Stable at room temperature
• Free of blood cell lines (see below)

Cons of cheek swabs:

• Lower total DNA yield than blood
• Potential for bacterial contamination from oral flora (minimized with proper technique)

Blood Draw

A blood draw provides a higher total DNA yield and high purity. It is the traditional collection method for clinical genetic testing.

However, blood has one significant limitation that is not widely appreciated: clonal hematopoiesis.

What Is Clonal Hematopoiesis?

Clonal hematopoiesis (CH) is an age-related condition in which a blood stem cell acquires a somatic mutation — a mutation that arises during a person's lifetime, not one inherited from their parents — and then expands, producing a population of white blood cells that carry that mutation.

The result is a mosaic situation: the blood contains a mix of normal cells and cells carrying the somatic mutation. In genetics, mosaicism occurs when an individual has two or more genetically distinct populations of cells that originated from a single fertilized egg.

This matters for genetic testing because somatic mutations in blood cells are not present in sex cells (sperm and egg) and therefore are not inheritable. A somatic mutation detected in a blood sample does not represent an inherited variant that can be passed to children — but it can be misinterpreted as one if the laboratory or clinician is not alert to this possibility.

How Common Is Clonal Hematopoiesis?

The likelihood that a blood sample reflects clonal hematopoiesis depends heavily on age and the sensitivity of the sequencing test used:

• Under age 40: Less than 1% chance
• Ages 50–60: Approximately 10–20% using standard clinical deep sequencing; up to 50–95% if ultra-sensitive error-corrected sequencing is used to detect very small clone fractions
• Ages 70+: Roughly 10–20% at standard clinical thresholds (variant allele fraction ≥ 2%, defining CHIP — clonal hematopoiesis of indeterminate potential); rising to over 50–60% in people in their 80s and beyond

Standard WGS and the Mosaicism Detection Limit

Standard clinical whole genome sequencing at 30x coverage means each region of the genome is read approximately 30 times. This level of coverage has a meaningful limitation:

Standard 30x WGS can only reliably detect mosaicism when more than 15–20% of cells carry the mutation.

If clonal hematopoiesis or another mosaic mutation affects only 2–5% of blood cells, standard WGS will miss it — the signal falls below the noise threshold and is treated as a sequencing error.

This is why standard consumer WGS platforms (such as Sequencing.com) will miss low-level mosaicism and copy number variations that exist at small clone fractions.

If a physician or researcher suspects a very specific, low-level mosaic mutation, they generally skip WGS and use targeted deep sequencing — such as a next-generation sequencing panel or digital droplet PCR. By focusing resources on sequencing just a few dozen genes at 5,000x to 10,000x coverage rather than the entire genome, they can confidently detect mosaic mutations present in fewer than 0.5% of sampled cells.

Why Genetic Insights Recommends Cheek Swabs

Because cheek cells are not blood cells, buccal DNA is free of clonal hematopoiesis artifacts. A somatic mutation present in blood stem cells will not appear in a cheek swab result — which means the result more accurately reflects the patient's inherited germline genome.

For the vast majority of genetic testing — including whole genome sequencing for inherited disease risk, pharmacogenomics, and hereditary cancer panels — Genetic Insights recommends cheek swabs as the preferred collection method.

The genotyping accuracy is equivalent to blood (>99.99%), the collection is non-invasive, and the result is not confounded by age-related blood cell mutations.

When Blood Is Required

There are specific situations where blood sampling is necessary or preferred:

• When the suspected genetic condition is limited to blood cells — for example, evaluating for somatic mutations in hematologic malignancies or myeloproliferative disorders
• Testing for hereditary alpha tryptasemia (HAT) and cKit mutations — these are always performed on blood samples
• Situations requiring very high DNA yield — certain specialized assays require more DNA than a cheek swab provides

For these indications, blood remains the appropriate collection method.

The Bottom Line

For most patients undergoing genetic testing at Genetic Insights, a cheek swab is the right choice. It is non-invasive, accurate, and avoids the age-related blood cell artifacts that can complicate interpretation of blood-based DNA results.

When blood is required — for blood-specific conditions or specific assays like HAT and cKit testing — we will let you know.

This article is for educational purposes only and is not a substitute for medical advice, diagnosis, or treatment.