Capillary blood: how testing from a fingertip works
The essentials at a glance
Capillary blood comes from the body's finest blood vessels, the capillaries. A small prick in the fingertip is enough to obtain a few drops. A laboratory uses them to determine the same values as from a venous blood sample—with a smaller sample volume and under conditions that you create yourself.
This article explains the procedure from the origin of the drop to the result: what a drop of blood actually contains, how sampling differs from having blood drawn at a medical practice, and which errors compromise the reliability of the results.
You will first learn what capillaries are. This is followed by a comparison with venous blood, the blood components in numbers, how sampling works, and the question of who this method is suitable for. The limitations of the procedure are discussed at the end.
What to expect in this article
1. What capillary blood actually is
2. How it differs from venous blood
3. What a drop of blood contains
4. Blood in numbers
5. How sampling at home works
6. What it costs in terms of reliability
7. Who this method is suitable for
8. Where to get a capillary blood test
9. What capillary blood cannot do
10. What matters in the end
Frequently asked questions
Sources
What capillary blood actually is
Capillaries are the finest blood vessels in the body. They form the transitional network between the arteries, which lead away from the heart, and the veins, which carry blood back to the heart.
This is precisely where the actual exchange takes place in the network: oxygen and nutrients pass into the tissue, while carbon dioxide and metabolic waste products are taken up. Capillary blood is therefore a mixture of arterial and venous blood.
The fingertip is commonly used as a sampling site because the capillary network is dense there and well supplied with blood. The earlobe is also used; in infants, the heel.
Key message
Capillary blood is not substitute blood, but the same blood at another point in the circulatory system—drawn from the network where exchange with the tissue takes place.
Where capillaries are located in the circulatory system
The circulatory system can be described as a distribution network. The arteries are the main roads leading away from the heart, while the veins are the return routes to it.
Between the two are the capillaries, forming the finest network of side roads. Their walls are so thin that substances can pass through—and that is precisely what they are designed for.
This position in the circulatory system is the reason for the mixture. Capillary blood contains components from the inflow and the return route because both come together at this point.
For the measurement, this is not a disadvantage but a characteristic the laboratory knows about and accounts for when selecting the reference range.
Why the fingertip specifically
The choice of collection site follows two practical requirements. The site must have a rich blood supply, and it must remain easy to reach when you collect the sample yourself.
Both apply to the fingertip. The capillary network lies just beneath the skin there, and the side of the fingertip can be reached comfortably with the other hand.
The puncture is made on the side, not in the center. The reason is sensitivity: The center of the fingertip contains more touch receptors, and a puncture there hurts significantly more without providing more blood.
The middle and ring fingers of the nondominant hand are commonly used. They are subjected to less strain in everyday life than the index finger and thumb, so the small puncture site is less likely to be bothersome.
How it differs from venous blood
Both methods provide blood, but they differ in the collection site, the amount, and who collects the sample. The table compares them according to the same five criteria.
| Criterion | Capillary blood | Venous blood |
|---|---|---|
| Collection site | fingertip, less often earlobe | vein in the crook of the arm |
| Sample volume | a few drops | one or more tubes |
| Who collects the sample | you, following instructions | medical professional |
| Location and timing | at home, you choose the time | medical practice or collection site, appointment required |
| Number of values that can be determined | limited by the sample volume | hardly limited by the sample volume |
The last line is the point rarely mentioned in advertising copy. A few drops cannot be used to determine an unlimited number of values, so a capillary blood test covers a fixed selection of values rather than an open-ended catalog.
How the journey to the laboratory differs
When blood is drawn at a medical practice, the tube usually reaches the laboratory the same day, often via a courier service. The journey is short and the conditions are known.
With an at-home test, the postal service handles this journey. This extends the time between collection and analysis, and the sample containers are designed specifically for this.
The simple rule for you is this: Put the sample in the mailbox on the same day, early enough for collection if possible. Mailing it on Friday afternoon adds two days to the journey.
Why the composition differs slightly
Because capillary blood comes from the transitional network, it contains components from both directions of the circulatory system. For some values, this results in slight deviations from a venous blood sample.
For the evaluation, this means that the laboratory uses reference ranges appropriate for the method actually used and the type of sample. The ranges on your own report are therefore always decisive.
For the question of how much individual values differ between the two types of samples, the sources reviewed for this article do not contain information from a German institution. That is why no figure is given here.
What is contained in a drop of blood
Blood appears to be a uniform red liquid, but it is a mixture of a liquid component and a cellular component. This ratio is why a few drops are sufficient for a measurement.
Verified source
“Blood consists of approximately 55% blood plasma and around 45% various blood cells.”
Institute for Quality and Efficiency in Health Care (IQWiG)
What does blood do?, as of 2023
Blood plasma is the liquid component. It contains the substances that a laboratory measures in many tests: hormones, vitamins, minerals, proteins, and blood lipids.
The cellular component consists of red blood cells, white blood cells, and platelets. More than 99 percent of the solid components of blood are accounted for by red blood cells (IQWiG, 2023).
Why plasma is the interesting part
For most questions people ask a blood test, the liquid component is crucial. Vitamins, minerals, hormones, and blood lipids are dissolved in the plasma, not in the cells.
This explains why a few drops can be enough. What is measured is not the amount of blood, but the concentration of a substance in it, and concentration is independent of sample size.
The limitation lies elsewhere: Each individual value requires a minimum amount for analysis. The more values that need to be determined, the more sample material is required, and this is exactly where a fingertip reaches its limit.
What distinguishes the three types of blood cells
Red blood cells contain hemoglobin and use it to transport oxygen. They live for around 120 days, according to IQWiG (2023). This explains why some blood values change only over a period of months.
White blood cells have a nucleus and are part of the immune system. They occur in different types and, according to the same source, live anywhere from hours to years.
Platelets are significantly smaller than red blood cells and are involved in blood clotting. They have a lifespan of five to nine days (IQWiG, 2023). They are the reason why a prick to the fingertip closes up again on its own.
Blood in figures
Three figures put the composition of a drop into perspective. They come from the same verified source.
Composition of blood
55 %
of blood is blood plasma—the liquid component in which the measurable substances are dissolved
45 %
are accounted for by blood cells, namely red and white blood cells and platelets
99 %
of the solid components of blood are red blood cells—they make up the vast majority
Source: Institute for Quality and Efficiency in Health Care (IQWiG), What does blood do?, as of 2023
To put the amount into perspective: A man weighing around 70 kilograms has approximately five to six liters of blood in his body (IQWiG, 2023). Compared with this amount, a few drops are hardly significant.
What these ratios mean for the measurement
The division into 55 to 45 percent is not a marginal detail, but the reason the procedure works at all. More than half of each drop is the fluid in which the substances being tested for are suspended.
The second figure explains the color. Because more than 99 percent of the solid components are red blood cells, their pigment, hemoglobin, completely dominates the visual impression.
And the lifespan of red blood cells—about 120 days—explains an experience many people have with blood values: Some values respond slowly. If you make a change today, you will see its effect after weeks at the earliest.
This leads to a practical recommendation for the second measurement. An interval of three to six months reflects a change; an interval of two weeks predominantly measures daily fluctuations.
How sampling at home works
The process consists of four steps. Each has a point at which the quality of the sample is determined.
Improve circulation
Warm hands release blood more easily. Cold fingers are the most common reason for obtaining too small a sample.
Set the timing
Note the date and time. With hormones, the timing determines how meaningful the result is.
Obtaining the sample
Prick the side of the fingertip, wipe away the first drop, then let the blood collect.
Shipping
Put it in the mailbox the same day. A sample that is left sitting loses its diagnostic value.
What to prepare before the finger prick
Lay everything out before you prick your finger. As soon as the blood appears, you will no longer have both hands free, and a drop that falls on the table is lost.
Preparation includes the containers from the kit, the adhesive bandage, a swab, and the completed accompanying form. Many kits require a code or registration, and it is better to take care of that beforehand than with a bloody finger.
Wash your hands and dry them completely. Residual moisture dilutes the sample just like disinfectant that has not yet evaporated.
And sit down. Feeling faint at the sight of blood is not unusual, and if it happens while you are sitting, nothing will happen.
Why the first drop is wiped away
The first drop often contains tissue fluid from the puncture site and traces of disinfectant. Both dilute the sample and skew the values.
That is why this step appears in every set of instructions, and why it is the one most often skipped. It takes two seconds and determines whether the sample is usable.
Why squeezing ruins the sample
When blood does not come out on its own, the instinct is to squeeze the finger firmly. That is exactly what causes problems: Forceful squeezing also draws out tissue fluid, reducing the proportion of actual blood.
The better approach is to improve circulation. Hold your hand under warm water, let your arm hang down briefly, and gently stroke from the heel of your hand toward your fingertip. After that, the drop usually comes on its own.
Chapter at a glance
The quality of a capillary blood sample is determined at three points: blood circulation before the finger prick, avoiding excessive squeezing, and wiping away the first drop. All three points are up to you, not the laboratory. If you follow them, you get a sample corresponding to one collected in a medical practice.
What compromises the reliability of the results
The most common problems do not arise in the laboratory but between the finger prick and the mailbox. Four of them occur regularly.
The first is an insufficient sample volume. If there is not enough blood for all the planned values, the laboratory cannot determine some of them, and the report remains incomplete.
The second is a delay in shipping. A sample that sits on the kitchen table for three days arrives at the laboratory in a different condition from one that was mailed the same day.
The third is the wrong timing. For values that vary throughout the day, such as hormones, the time determines comparability. How much this matters is explained in our article How is testosterone measured?.
For vitamins and minerals, the time of day is less critical; instead, something else matters: whether you took a supplement shortly before collecting the sample. A note about this belongs on the same piece of paper as the time.
The fourth is the missing note. Without the date, time, and, for women, the day of the menstrual cycle, it is later difficult to compare one result with a second.
What a laboratory does when the sample is insufficient
If too little material arrives, the laboratory determines the values it has enough for and reports the rest as undeterminable. A report with gaps is the result, not an error message.
Whether a replacement kit is provided is determined by the respective provider. This question should be clarified before purchase, because in case of doubt it determines whether a second order is needed.
The objection is justified: That sounds like there are many ways to do something wrong. Even so, something else is decisive. All four sources of error can be ruled out with warm hands, a note, and a timely trip to the mailbox.
How to recognize useful instructions
Not every kit’s instructions are equally thorough. Three points distinguish a useful guide from one that leaves the user without support.
First, it must explain what to do with the first drop. If this instruction is missing, the step at which most samples become diluted is missing.
Second, it must state how much blood is needed, visibly on the vessel rather than in milliliters. A marking you can see while collecting helps more than a number in the text.
Third, it must specify the shipping date. Instructions describing the return process without mentioning the day of mailing leave out the most common source of error.
Who this option is suitable for
Suitable for you if …
you are looking for a baseline for your own monitoring and cannot or do not need to get an appointment for a blood draw.
you want to determine the sample timing yourself, for example, to measure a hormone in the correct morning window.
you are planning a change and want to track the progression with one measurement before and one afterward.
Not recommended if …
you have acute symptoms. In that case, an appointment is the right order, not the sample in the mailbox.
you have a blood-clotting disorder or take blood-thinning medication. Talk to your doctor's office beforehand.
you need many values at the same time. The sample volume from a fingertip limits the number of measurable values.
Where to get a capillary blood test
All blood tests by mybody®x (MYBODY Lab GmbH) use capillary blood. That is why a kit can be sent by mail and no medical practice is needed for collection.
The quality of a capillary blood sample is determined in the two minutes before the prick, not in the laboratory.
The quality of a capillary blood sample is determined in the two minutes before the prick, not in the laboratory. Warm hands, a set time, and avoiding squeezing cost nothing and contribute to the entire result.
Capillary blood test
VitalCheck | Complete Nutrient & Mineral Test
18 biomarkers from capillary blood related to the supply of vitamins, minerals, and trace elements. What the test does not do: It does not provide a diagnosis, and the sample volume from a fingertip limits the number of measurable values to this fixed selection. An abnormal result should be assessed by a doctor.
Laboratory evaluation 3–5 business days after sample receipt
Product page information, accessed on 27 August 2026
What happens after shipping
In the laboratory, the sample is first checked for quantity and condition. Only then does the actual analysis of the individual values begin.
The laboratory analysis takes three to five business days after receiving your sample. Kit shipping at the beginning takes an additional one to three business days; the two periods are stated separately because they describe different things.
In the end, you receive a report with your values and the laboratory's reference ranges. These ranges belong to the method used, which is why they are the relevant ones, not the figures from an article.
What the report does not contain is an interpretation in the context of your medical history. For that, you need a consultation, and you should bring the printout with you.
How such a test fits into everyday life and what others experienced with it is covered in our article At-home blood test: experiences. This article focuses on the procedure.
What capillary blood cannot do
The first limitation is quantity. A few drops can determine a fixed selection of values, not any desired panel. Anyone who needs many values measured at once cannot avoid a venous blood sample.
The second limitation is the sampling itself. You perform it yourself, so the sources of error are also yours to manage. In a practice, trained professionals handle this part.
The third limitation is interpretation. A capillary blood test provides a result, not a diagnosis. What a value means in the context of your medical history is determined in a conversation.
The fourth limitation concerns what a blood value can fundamentally show. It describes a state at the time of sampling, not its cause. Whether a low value results from diet, impaired absorption, or increased consumption is not shown in any report.
The fifth limitation is the selection itself. A test covers the values it includes and says nothing about all the others. An unremarkable result therefore means that the measured values are unremarkable, not that nothing is wrong.
When a venous blood sample is the right choice
There are situations in which a fingertip sample is not enough. The clearest is a broad examination panel with many values measured at once, as is customary when a practice is investigating a condition.
The second is monitoring an existing treatment. That belongs in the hands of the people providing the treatment, because the result has immediate consequences there.
And the third concerns anyone for whom sampling itself carries a risk: in cases of coagulation disorders and when taking blood-thinning medication, this question should be discussed with a doctor beforehand.
And one boundary concerning our own scope: the reviewed sources contain no figure for how much individual values differ between capillary and venous blood. This article therefore gives no estimate instead of guessing.
What matters in the end
If you take away just one action from this article, let it be this: Hold your hands under warm water for two minutes before the prick. No step in the entire sampling process offers a better balance of effort and effect.
The reason is simple. Most failed samples are due to too little blood, and the most common cause is cold fingers. Solving that issue solves the problem before it arises.
The second point takes even less time: Write down the date and time as soon as the sample is in the envelope. This line determines whether a second measurement in six months will provide meaningful information or merely produce another number.
Together, both steps take less than five minutes and eliminate any concern about the procedure. The laboratory analysis is the part you do not need to worry about.
It began with the question of how a measurement from the finger works. The answer is less remarkable than the term capillary blood might suggest: It is the same blood, collected from a different location. What makes the difference is not the vessels, but the two minutes beforehand.
Frequently asked questions
What exactly is capillary blood?
Capillary blood comes from the capillaries, the finest blood vessels in the body. They form the transitional network between arteries and veins, where exchange with the tissue takes place. Capillary blood is therefore a mixture of arterial and venous blood. A small prick in the fingertip is sufficient for collection; more rarely, the earlobe is used.
Is a finger-prick test just as informative as one from a vein?
The laboratory determines the same values from both types of sample, using reference ranges appropriate to the method employed. The difference lies in the amount and in who collects the sample: a limited selection of values can be determined from a few drops, and you collect the sample yourself rather than a healthcare professional. As for how much individual values differ between the two types of sample, the reviewed sources provide no figure.
Why should I wipe away the first drop of blood?
Because it often contains tissue fluid from the puncture site and traces of disinfectant. Both dilute the sample and shift the values. The step takes two seconds and determines whether the sample is usable. For the same reason, you should not squeeze the finger forcefully: squeezing causes additional tissue fluid to escape.
What should I do if too little blood comes out?
The solution lies in improving blood flow, not applying more pressure. Hold your hand under warm water, let your arm hang briefly, and gently stroke from the base of your palm toward your fingertip. A second finger prick on another finger is better than squeezing the first one hard. If the amount is still insufficient for all the specified values, the laboratory may be unable to determine some of them.
What is blood actually made of?
Approximately 55 percent consists of blood plasma and around 45 percent of blood cells (IQWiG, 2023). The plasma contains the substances that a laboratory usually measures: hormones, vitamins, minerals, proteins, and blood lipids. More than 99 percent of the solid components are red blood cells; they live for approximately 120 days. A man weighing around 70 kilograms has approximately five to six liters of blood in his body.
Next step
A baseline value you determine yourself
If you want to assess your vitamin and mineral status, VitalCheck provides a starting point from just a few drops of capillary blood. It does not replace medical evaluation.
To VitalCheck Complete Read about others' experiencesRead more
You might also be interested in this
What others have experienced and what to look for when choosing.
Why the time of day when a sample is taken determines the significance of hormone results.
Sources
- Institute for Quality and Efficiency in Health Care (IQWiG): What does blood do? (as of 2023) – gesundheitsinformation.de
- Institute for Quality and Efficiency in Health Care (IQWiG): Understanding laboratory values correctly (as of 2025) – gesundheitsinformation.de
The verbatim quotation about the composition of blood, the proportions of 55 and 45 percent, the proportion of more than 99 percent red blood cells among the solid components, the lifespans of approximately 120 days and five to nine days, and the stated blood volume of five to six liters come from source [1]. The statement that reference ranges depend on the laboratory and method comes from [2]. The information about collecting samples from the fingertip describes the usual procedure and follows the instructions included with the test kits. Information on price, biomarkers, sample type, and laboratory comes from the mybody®x product page, accessed on 27.08.2026; processing times follow the standard guideline for blood tests. Both sources were accessed and reviewed on 27.08.2026.
mybody®x Editorial & Expert Team
Laboratory diagnostics Blood analysis interpretation Nutritional science Nutrigenetics
This article was created by the mybody®x editorial and expert team. The team combines laboratory diagnostics, nutritional science, and the interpretation of blood analyses. Those who contribute to it are listed on the authors page.
Published on 27.08.2026 · Last updated on 27.08.2026
The content is intended for general information and does not replace medical advice, diagnosis, or treatment. Reference ranges depend on the laboratory, method, and age—the information on your report is always authoritative.
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