University of Sussex Students' Newspaper

Paper strip reveals blood type

Daniel Stuart

ByDaniel Stuart

Mar 31, 2017

Not many people reading this article will know their blood type. However, in some medical emergencies, this is a vital piece of information. Mismatched blood transfusions can have disastrous, consequences for a patient due to markers on blood cells called ‘antigens’. These molecules exist on many different substances including toxins and bacteria, and are used by the immune system to decide whether to produce an immune response such as sending antibodies.

If a patient is given a blood transfusion with a blood type different from their own, antibodies are made against it as the immune system interprets the donor blood as a toxin. This is known as ‘ABO incompatibility reaction’ and causes the almost immediate onset of symptoms including fever and chills, nausea and muscle aches.

The type of antigen on our blood cells is used in lab tests to define which blood type we are: A, B, AB or O, which can in turn be positive or negative via the presence or absence of a separate D antigen.

Currently, this test requires a laboratory and takes 10-20 minutes which, while not a great amount of time, in an emergency situation this is an eternity. Therefore, the O blood type is used as it contains no antigens and will not set off a response from the immune system. This blood type is rare though, and so a more economical system for testing blood type would be a game changer for healthcare globally.

Recently, paper strip blood tests for diseases such as malaria have been developed, and this logic has been taken on a step by Hong Zhang at the Third Military Medical University in China for blood tests. By combining the antibodies that detect the blood-type antigens with a dye, he has created a test that can define a blood type and is over 99.9% accurate.

Furthermore, while the disease testing strips are still required to be sent back to a lab, the blood test strips act within 30 seconds on the spot which means a lab is not required. This will allow blood tests to be performed swiftly in situations such as motor vehicle accidents or war zones and will greatly reduce the reliance on the rare O-negative blood type, in turn saving a huge amount of time and money for health services.

The strips are very simply interpretable, with three boxes testing for each of the A, B and D antigens, which turn a teal colour if present, or brown if not and Zhang predicts that these could be in use within 1-2 years.

The invention of these blood test strips could, in turn help revolutionise the afore mentioned disease tests. As the combination of antibodies and dye to detect antigens could be used more specifically for individual disease antigens.

However in some situations O blood may still be the best option as there is always a risk of human error leading to the wrong type of blood being given to a patient. So while these tests could reduce demand for O blood it is likely to remain the preferred choice for emergency departments.

The success of this strip test could transform not only emergency medicine but perhaps even medicine in remote countries or areas where lab equipment is not so freely available.

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