Does Posting a Blood Sample Affect Your Results?

Does Posting a Blood Sample Affect Your Results?

Part 3 of our series on home blood testing. In Part 1, we looked at why not every test suits a postal finger-prick kit. In Part 2, we looked at how finger-prick and venous results compare.

Short answer: It can, but it depends on the test, how long the sample is in transit, and the temperature it experiences. Research shows some measurements hold steady for a day or more, while others change within hours. This is why laboratories validate each test for postal transport and give clear return instructions.

Why does time in transit matter?

Blood is living material. After collection, the cells in a sample keep working, and substances move between the cells and the liquid around them. Over time this can change what the laboratory measures. Warm temperatures speed these changes up, and cooler storage generally slows them down.

A home kit can spend hours or days between collection and analysis, including time in a postbox and sorting network. That is the main reason postal sample stability is studied.

What does the research show?

Most stability research has been done on venous samples stored under controlled conditions, but the principles apply to any blood sample left to wait before analysis.

• A large pooled analysis. A 2017 systematic review and meta-analysis in EBioMedicine pooled 89 studies of adult blood samples. It found blood count measurements were generally reliable for at least 24 hours, and some for up to three days. Results from a chemistry panel were reliable only within about 12 hours when stored at 4 °C, and were less stable at room temperature. The authors concluded that refrigeration is the better choice for longer storage.
• Blood counts over 48 hours. A 2021 study in the Journal of Medical Biochemistry stored samples at three temperatures for 48 hours. Some measurements stayed stable throughout, while others changed at room temperature, with the earliest changes appearing after around 12 hours. The authors recommended 4 °C for storage of up to 12 hours.
• Warm-weather shipping. A 2025 study in Practical Laboratory Medicine tested samples at 30 °C, similar to a warm summer postal journey, and at 0 °C, similar to shipping in contact with melting ice. After one day at 30 °C most of the 20 common markers stayed within accepted limits, but a few did not. After three days, fewer than half of the markers in uncentrifuged samples did. Separating the sample by centrifuge before storage improved stability for several markers.
• Capillary samples specifically. A 2023 study in Diagnosis compared capillary and venous samples from 296 patients, and also tested 24-hour stability of capillary samples at room temperature. A 2023 study in the International Journal of Laboratory Hematology compared capillary and venous blood counts and examined how storage temperature affects stability for up to 7 days.
• Stabilising at the point of collection. A 2025 study in Scientific Reports described a capillary kit that stabilised the sample at collection, keeping it usable at room temperature for up to 14 days. That kit was designed for drug monitoring rather than routine blood tests, so it shows what is possible rather than a general solution.

Which things affect stability?

• Temperature: warm conditions generally speed up changes in a sample. Cool storage generally slows them.
• Time: the longer the delay, the more likely a result is to drift.
• The test itself: some measurements are robust, and others are sensitive. This is why stability has to be checked test by test.
• Whether the sample has been separated: separating the liquid part of the blood from the cells before storage can protect some results.
• Sample damage: haemolysis (damaged red cells) is more common in capillary samples and can affect certain results.
• The collection device: some devices are designed to stabilise a sample, or to keep cells and liquid apart.

How do laboratories protect results?

Responsible laboratories typically:

1. Validate each test for the sample type and transport conditions it accepts.
2. Use suitable collection devices and clear packaging.
3. Give simple return instructions, including when to post and what to avoid.
4. Process samples promptly on arrival.
5. Check sample quality and reject or flag samples that are damaged, delayed or insufficient.
6. Apply quality control throughout analysis, with the laboratory regulated for quality.

What can you do?

• Follow the collection and packaging instructions exactly.
• Post your sample as instructed, and avoid posting it just before a weekend or bank holiday if your provider advises against it.
• Keep your sample out of direct heat and sunlight before posting.
• Contact the laboratory if your sample is delayed.

Frequently asked questions

Does posting a blood sample affect the result?
It can for some tests. Time and temperature in transit affect certain results more than others. A good laboratory validates each test for postal transport.

How long can a blood sample be stored before testing?
It depends on the test and the conditions. Research shows some measurements hold for a day or more, while others change within hours, especially in warm conditions.

Does hot weather affect home blood tests?
Warm temperatures speed up changes in a blood sample, which is why laboratories test stability under warm conditions and give guidance on handling.

Why do laboratories reject some samples?
Samples may be rejected if they are too small, damaged, clotted, delayed or labelled incorrectly, because the result might not be reliable.

Are home blood tests as reliable as tests at a clinic?
For validated tests, evidence supports close agreement. Reliability depends on the test, the collection technique, transport conditions and the laboratory.

About London Health Company

London Health Company (LHC) is a CQC-regulated private blood testing laboratory in London. Our home finger-prick kits are analysed in-house. Browse our blood tests.

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

Next in the series: Part 4: how to take a good finger-prick sample at home.

References

1. Wu D-W, Li Y-M, Wang F. How long can we store blood samples: a systematic review and meta-analysis. EBioMedicine. 2017;24:277-285. doi:10.1016/j.ebiom.2017.09.024
2. 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
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. Maroto-García J, et al. Analysis of common biomarkers in capillary blood in routine clinical laboratory. Preanalytical and analytical comparison with venous blood. Diagnosis (Berl). 2023. doi:10.1515/dx-2022-0126
5. Doeleman MJH, Esseveld A, Huisman A, de Roock S, Tiel Groenestege WM. 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. Komninos N, De Chiara S, Checa A, Wiklander O, Rydberg P, Hedayati E. Development and evaluation of a novel capillary blood collection method for decentralized therapeutic drug monitoring using the True Dose kit. Sci Rep. 2025. doi:10.1038/s41598-025-20951-5