What causes blood sample errors?

Here are the three most common causes of blood sample errors and how you can help to avoid them.

Blood sample errors are a common occurrence and can happen for a variety of reasons. Although they are most likely to occur if a sample has been collected via the finger-prick method, errors can still arise when a venous collection method has been used (although this is far less common). Finger-prick tests are just as accurate as venous blood tests if collected properly.  

Here are the three most common causes of blood sample errors and how you can help to avoid them.  

The three most common causes of blood sample errors: 

1. A clotted sample

Clotting (also known as coagulation) is when your blood turns from a liquid to a gel. It is your body’s natural defence in stopping you from bleeding excessively [1]. So, what is a clotted blood sample? 

A clotted blood sample can happen if: 

  1. Your blood has not been mixed thoroughly after collection  
  2. You have taken a while to collect your sample and the blood has clotted before you have mixed it 

To avoid your blood sample clotting, carefully invert your tube five times (without shaking it). We also recommend you give the container a gentle swirl after each drop of blood has been collected to help the sample mix together.  

2. A haemolysed sample

A haemolysed sample can occur when some of the red blood cells burst and the haemoglobin (the protein in your red blood cells that carries oxygen to the body) escapes and spoils the surrounding sample [2]. 

With a finger-prick sample, your sample may become haemolysed if you: 

  • Squeeze too hard  
  • Scrape your finger on the side of the tube instead of letting the droplets fall in 

Take your time and avoid both of the above reasons to reduce your chances of a haemolysed sample and having to re-take your test.  

Venous blood tests can also be affected by haemolysis when there are difficulties in taking the sample, although this is far less common.  

3. An insufficient blood sample

An insufficient sample simply means that there is not enough blood to test. When the laboratory receives your sample, it is spun and separated into the blood cells and liquid (serum) that surrounds the cells. If the amount of blood taken is too small, the lab will struggle to produce enough serum to test.  

To reduce your chances of this, follow our instructions carefully. Each test will tell you which line you need to fill your sample to. If you are struggling to take your sample, we have put together some top tips on how to take a finger-prick sample.

What happens if there is an error with my sample? 

If our laboratory finds an error with your sample, we'll notify you by email as soon as possible. There is absolutely no reason to worry. 

If it was your first time collecting a finger-prick test, many of our customers have a better success rate on their second attempt. You can order a new finger-prick test, completely free of charge by calling our Customer Care team (making sure you have your order number and PID to hand). 

Alternatively, if you would like to upgrade your order and opt to visit one of our partner clinics or arrange a home visit, our Customer Care team will be able to organise this for you.   

How to take a finger-prick blood sample 

Visit our top tips for taking a finger-prick sample blog for help and advice.  


  1. Hematology.org. 2022. Blood Clots. [online] Available at: <https://www.hematology.org/education/patients/blood-clots> [Accessed 15 August 2022].  
  2. Wan Azman, W., Omar, J., Koon, T. and Tuan Ismail, T., 2019. Hemolyzed Specimens: Major Challenge for Identifying and Rejecting Specimens in Clinical Laboratories. Oman Medical Journal, 34(2), pp.94-98.