DNA test and blood test: what's the difference?

Most of the time, when people hear about genetic testing, they ask the same question: How is it different from a regular blood test? Both involve measuring your body's parameters - both give a "result." But they are different tools that analyze fundamentally different things.

If you have already encountered the situation where you regularly take tests, get "normal" results, but questions about your well-being or predispositions remain unanswered, -article about why vitamin deficiencies are not always solved by supplements, demonstrates this difference with specific examples.

What does a blood test show?

A blood test records the current state of the body. It measures how much of a particular compound – a vitamin, a hormone, an inflammatory marker, cholesterol – is in the blood right now, at the time of the test. This is useful and important information. 

But the result depends on many variables: what you ate the day before, whether you took supplements or medications, how much sleep you got, whether there is an inflammatory process at the time of the analysis. Take the same analysis a week later - and the indicators may differ. This is not a problem with the method, it is its nature: a blood test records a dynamic state that is constantly changing.

That is why a blood test is a good answer to the question “what is happening now”, i.e. is there a deficiency, is there inflammation, is the thyroid gland functioning normally today, etc. But it hardly explains “why is this happening” and “what is my predisposition to this”. 

What does a DNA test show?

A DNA test analyzes genetic variants – differences in the structure of DNA that a person is born with and that do not change throughout life. This is not an analysis of the state of the organism, but an analysis of its “settings”.

You can take a DNA test once and the result will remain relevant regardless of what you ate, how you slept, or whether you developed any illnesses after the test. Your genetic profile is unchangeable.

What exactly is being analyzed?

Modern genetic tests for the general population – so-called DTC (direct to consumer) tests – examine hundreds of thousands of genetic variants simultaneously. They are used to calculate polygenic risk scores (polygenic risk scores, PRS) – numerical indicators of where a particular person is among the general population according to one or another parameter: susceptibility to cardiovascular diseases, peculiarities of vitamin absorption, reaction to stress, quality of sleep, etc. (Kullo et al.,Night Fox Genet, 2022).

Key point: DNA testing does not diagnose disease. It shows hereditary predispositions and characteristics – something to consider when choosing a lifestyle, diet, or when talking to a doctor.

Genetic testing does not replace laboratory examinations.

This is perhaps the most important thing to understand before jumping to any conclusions.

A blood test and a DNA test answer different questions. One without the other is an incomplete picture.

Here is a specific example. A person has regular blood tests: the level of vitamin D in the blood is normal. But she wakes up tired every morning, despite a full night's sleep, feels constant lethargy and has difficulty concentrating. It turns out that the sensitivity of her cells to vitamin D may be genetically reduced - and then a normal level in the blood does not mean that the body uses it effectively (Usategui-Martín et al.,Nutrients, 2022). The blood test showed a “normal.” A DNA test would explain why this normal doesn’t feel like normal.

It works the same way in the other direction: if a genetic test reveals an increased predisposition to a certain condition, it does not mean that a person is already sick or will definitely get sick. A predisposition is not a diagnosis. What is really happening in the body now is what a blood test and other tests will show.

One tool explains the “why,” the other measures the “what.” Together, they provide a more complete picture and deeper understanding than either alone.

What do the numbers in a genetic report mean?

When people see a genetic report for the first time, their first reaction is often one of confusion: What does “75th percentile” mean? Is that bad or good?

A percentile in a genetic report is a position among people with a similar genetic profile. The 75th percentile for susceptibility to a condition means that 75% of people in the comparison group have a lower genetic predisposition than you, and only 25% have a higher one. This is not a judgment or a diagnosis. It is context.

It is important to understand several things at once:

• A high genetic predisposition does not mean that the disease will necessarily develop. Lifestyle, nutrition, physical activity are all independent factors that significantly influence the realization of genetic predispositions (Merino et al.,PLoS Med, 2022).

• Low susceptibility is also not a guarantee. A person with a low genetic risk of cardiovascular disease can develop the disease if they ignore lifestyle factors for years (Iribarren et al.,Int J Cardiol Res Pract, 2024).

• A genetic report is not a medical diagnosis. It provides context for a conversation with a doctor, not a replacement.

That is why a properly interpreted genetic report always presents results in a relative context, not as an absolute verdict.

How these two tools work together

The greatest value of a DNA test is not the fact of having a result, but how that result can be used.

A person who knows their genetic profile comes to the doctor with specific questions. Not "I think something is wrong," but"I have a genetically reduced efficiency of magnesium absorption - should I adjust my supplements?"or"I have an increased tendency to lipid metabolism disorders - what indicators should I pay attention to in blood tests?".

This changes the nature of the conversation. The doctor receives not just symptoms and complaints, but genetic context, which helps to more accurately interpret the results of the examinations. The patient receives not general recommendations, but answers and solutions that are specific to his body.

 Blood tests are not going away – they remain the main tool for monitoring the current condition. DNA testing qualitatively complements them, explaining the hereditary context.

If you are wondering what exactly tendencies and characteristics can be analyzed, 

→ view available tests and panels.

A DNA test does not replace a blood test.

A blood test and a DNA test solve different problems. A blood test measures the state of the body now – and this state changes. A DNA test analyzes hereditary characteristics that remain unchanged throughout life. The first answers the question “what is there”, the second – “why is it so”. Together they give the doctor and the patient the information to make informed decisions. Genetic predisposition is not a sentence, but it is a context that is worth knowing before symptoms appear.

List of sources

1. Kullo IJ et al. (2022). Polygenic scores in biomedical research. Night Fox Genet, 23:524–532. https://doi.org/10.1038/s41576-022-00470-z

2. Usategui-Martín R et al. (2022). Vitamin D Receptor (VDR) Gene Polymorphisms Modify the Response to Vitamin D Supplementation: A Systematic Review and Meta-Analysis. Nutrients, 14(2):360. https://doi.org/10.3390/nu14020360

3. Merino J et al. (2022). Polygenic scores, diet quality, and type 2 diabetes risk. PLoS Med, 19(4):e1003972. https://doi.org/10.1371/journal.pmed.1003972

4. Iribarren C et al. (2024). Interplay between lifestyle factors and polygenic risk for incident coronary heart disease in a large multiethnic cohort. Int J Cardiol Cardiovasc Risk Prev, 23:200350. https://doi.org/10.1016/j.ijcrp.2024.200350