Why Can't Every Blood Test Use a Finger Prick?

Short answer: Finger-prick (capillary) samples give results that closely match venous blood for many common tests. The main limit for home sample collection followed by lab testing is stability: some markers change during the time a sample spends in the post, so not every test suits a postal finger-prick kit.

What can a finger-prick sample be used for?

Recent peer-reviewed studies show close agreement between finger-prick and venous (arm) blood across a wide range of routine tests. A 2025 study in the *Journal of Applied Laboratory Medicine* compared 39 different markers and found capillary results equivalent to venous comparators. A 2025 study in *Clinical Chemistry and Laboratory Medicine* compared 34 routine markers and found most results fell within accepted limits. A 2025 systematic review of 26 studies also found strong overall agreement, and less pain with finger-prick collection.

Why can't every test use a finger prick?

1. Transport time and temperature.  A home kit is collected, posted and received by the laboratory, often over one to three days, with limited control over temperature along the way. Some markers hold steady during this time, while others drift.

2. Some markers are more stable than others.  Studies of stored blood samples show that warm temperatures and longer delays affect some markers more than others. In one 2025 study simulating a warm summer postal journey, most markers stayed within accepted limits after one day, but fewer did after three days.

3. Blood cell measurements change with time.  Research on blood counts shows that some measurements stay stable for 48 hours or more, while others change within hours when samples are stored at room temperature. Cooler storage generally helps.

4. Sample quality.  Capillary samples are more likely than venous samples to show haemolysis (damaged red cells), which can affect some results. Careful collection technique and quality checks in the laboratory help manage this.

5. Each test has to be validated. Agreement between capillary and venous blood has to be checked marker by marker. Research shows strong agreement for many tests and weaker agreement for some, so a laboratory should confirm that each test is suitable for the sample type it accepts.

How can the risk be reduced?

Stability depends on how the sample is collected, packaged and returned. Laboratories reduce risk by validating each test for postal transport, using suitable collection devices, processing samples promptly on arrival, and giving clear posting instructions. Research is also exploring collection systems that stabilise the sample at the point of collection.

Which tests usually still need a blood draw?

Tests whose results change quickly in transit, or that are sensitive to sample damage, may be better suited to a venous draw taken and processed locally. A testing provider can tell you which tests are validated for postal finger-prick collection.

Frequently asked questions

Can all blood tests be done with a finger prick?

No. Many common tests can, but some markers are less stable during postal transport or haven't been validated for capillary samples.

Does posting a blood sample affect the result?

It can for some markers. Time and temperature in transit affect certain tests. A good laboratory validates each test for postal transport and gives clear return instructions.

Is a finger-prick result less accurate?

For validated tests, studies show close agreement with venous blood. Accuracy depends on the test, the collection technique, transport conditions and the laboratory.

How do I know if a home test is validated for finger-prick samples?

Choose a provider that tells you which sample type each test uses and is regulated, such as a CQC-regulated laboratory.

What if my result is unexpected?

Speak to a healthcare professional. They may recommend repeating the test or confirming it with a venous sample.

About London Health Company

London Health Company (LHC) is a CQC-regulated private blood testing laboratory. Our home finger-prick kits are analysed in-house and we have done extensive research as well as our own validation to narrow down the biomarkers we test using capillary blood.  

This article is for general information and is not medical advice.

References

1. Doeleman M, et al. Comparison of capillary finger stick and venous blood sampling for 34 routine chemistry analytes. *Clin Chem Lab Med*. 2025. doi:10.1515/cclm-2024-0812

2. Equivalence between capillary blood and venous blood test results using miniaturized assays and novel collection methods. *J Appl Lab Med*. 2025. https://academic.oup.com/jalm/article/10/5/1090/8131433

3. Iacovetti G, et al. Assessment of the stability of 20 biochemical analytes in serum and whole blood samples after storage at nonstandard temperatures. *Pract Lab Med*. 2025;48:e00514. doi:10.1016/j.plabm.2025.e00514

4. Unalli Ozmen S, Ozarda Y. Stability of hematological analytes during 48 hours storage at three temperatures using Cell-Dyn hematology analyzer. *J Med Biochem*. 2021;40(3):252-260. doi:10.5937/jomb0-27945

5. Doeleman MJH, et al. Stability and comparison of complete blood count parameters between capillary and venous blood samples. *Int J Lab Hematol*. 2023;45(5):659-667. doi:10.1111/ijlh.14080

6. Comparison of laboratory results and pain perception in self-sampled capillary blood versus venous blood sampling: a systematic review and meta-analysis. 2025.