In a packed emergency department, timing is crucial. If an injured patient enters with catastrophic blood loss, they need a transfusion, and quickly.
Many people don’t know their blood type, however, so the treatment must be delayed until they can be typed. In a war zone, it can be hard to access the equipment necessary to complete a blood typing test. In answer to this, a research group in China has developed a simplified typing test that does not require special lab equipment and, most importantly, takes only 30 seconds.
Blood types are so named due to antigens present on the red blood cells – A, B, AB (both), O (none), and then D (positive or negative). If the wrong blood type is introduced into the blood stream via transfusion, it can have devastating, even fatal, consequences.
The recipient’s immune system recognises the foreign antigen on the donor cells and mounts a defence, including inflammation and clotting as antibodies try to subdue the ‘invading’ cells. To prevent this, most emergency rooms stock up on the ‘universal donor’ O-negative, which carries no antigens and can be safely transfused to anyone.
However, stocks of O-negative are in high demand and, with only around 10 per cent of donors in the UK with this blood type, the supply is under constant pressure.
Current blood tests rely on centrifuges to separate the red blood cells from the serum: a piece of equipment not always available in developing countries or on the front lines during conflict. This process is also actually two separate tests which must be carried out in sequence, thus delaying the result.
The cells are mixed with each antibody solution and checked for reactivity. Then the cell-less serum is mixed into the blood type found by the first test, to double-check the reaction. This can take from 20 minutes to a day, depending on access to equipment and trained personnel, but, in a traumatic injury, availability of the correct blood type for transfusion may be needed much more urgently that this.
The Chinese research group, led by Hong Zhang at the Third Medical Military University in China, used a paper strip that has been dosed with the antibodies against each type, mixed with a blood-reactive dye.
Upon application of a drop of blood, the blood soaks through the paper and reaches each dosed section. When the blood reaches an antibody that reacts to the antigens in the blood, the dye turns from brown to teal. Thus, type AB would turn both areas teal, type O would remain brown, and the A and B types would change different areas of the strip.
This whole procedure takes around 30 seconds, can use blood without any prior steps, and the colour change is detectable even for those with red-green colourblindness.
In the lab, this test has proved 99.9 per cent effective at detecting the correct blood type in a sample size of 3,550.
However, it is still in the proof-of-concept stage, although the team are confident to push for its wide release in the next two years.
The sterility and control of a lab environment is extremely different to an emergency situation, so testing in adverse conditions will be required. The risk of contamination by other fluids that can replicate the reactivity is also an issue that needs to be investigated further.
The team also hope to expand their test to include other, rarer types. However, this test offers a potential lifesaver in many areas of emergency medicine, with a cheap and quick result for only a drop of blood.
Image: United States Navy