Blood typing in a jiffy

Last Updated 05 July 2010, 12:17 IST
Blood typing in a jiffy

Blood transfusion became a useful life saver only after 1901, when blood groups were discovered. Till then, transfusion sometimes helped patients recover from blood loss or survive surgery, but it often led to their dying because of the transfusion, rather than the loss of blood. This changed when the vital factor of the correct blood group was discovered. But still, the process of testing the blood for the correct blood group is a laboratory affair and takes some time, which can compromise the patient's chances.
Mohidus Samad Khan, George Thouas, Wei Shen, Gordon Whyte, and Gil Garnier, at Monash University, Australia report in the journal of the American Chemical Society their innovation of testing for the blood group with a strip of special paper - which can be quick and easily done by a lay person.

Blood groups

The Austrian, Karl Landsteiner was working with the the discovery that “proteins”, the building blocks of living things, “are characteristic of each species.” In fact, he noted, different organs contain special proteins, and it appeared that different parts of an animal of even the same species need particular materials for their construction. This was so much unlike man-made machines, which were the rage in the 1900s, where different parts could be made from the same material!

To test out whether this differentiation extended to individuals of the same species, Landsteiner tried mixing samples of blood serum and red blood cells of different persons with each  other. In many cases, he noticed, it was as if the blood of a person had been mixed with her own blood. But in some cases, the blood formed clusters, or lumps, an effect called agglutination, as if the blood being mixed were of different species!

With different combinations and clever detective work, Landsteiner showed that there were 4 blood groups, A, B, AB and O, in human blood, which could be combined or could not.

Thus, persons with blood groups A or B could receive blood of the same group or of group O. Persons with AB could receive any kind of blood. But persons with O could receive only O. But then, O group blood could be received by any group! AB was then the universal recipient while O was the universal donor.  With the wrong blood group, the transfused blood formed 'clusters', which affected circulation or the functioning of other organs and usually led to the patient’s death.

Proteins at work

We now know that human blood cells have specific surface proteins that mark them as A, B, AB or O. These proteins are antigens, or agents that cause specific immune reactions when injected into another body. The blood serum, at the same time contains antibodies, or agents that cause a reaction against specific antigens in foreign bodies

  Thus, A and B group blood cells have A and B antigens respectively, but the serum of each group has antibodies that act against the other group, ie, group A has B antibodies and group B has A antibodies. And group AB has both the antigens but no antibodies. And group O has no antigens but both antibodies.

The result is what we have seen - that A and B can receive blood of their own type, which has the right antigens, or of group O, which has no antigens. Group AB, which has no antibodies, can receive any kind of blood. And group O, which has both antibodies can receive blood only of its own kind. But as it has no antigens, it can be received by any group.

For this work, Landsteiner received the Nobel Prize for medicine in 1930.

Testing for blood group

While knowing the blood group thus makes a certainty out of the value of blood transfusion, there remains the need to test the donor and the recipient for the blood group. The usual method is to take a blood sample and mix it with reagents, one which contains the antibodies for the antigens of group A, and the other which contains the antibodies for the antigens of group B. If the sample clumps, or aggregates, with either, the blood group is identified, as A or B. If it clumps with both, it is O, if with neither, it is AB.  In practice, blood is first typed by this comparison with typed reagents. Next, in a process called reverse typing, the sample is mixed with blood of known type. Again, clumping will determine the blood type and confirm the results of the first test and make sure.

These tests are carried out in the laboratory, by trained technicians, facilities that are normally available in hospitals. But this may not be true emergencies or at accident sites, and in such cases, delays in making sure of the blood type can be dangerous.

Dip-stick testing

The innovation reported in the journal, Analytical Chemistry, consists of testing blood simply by depositing a drop of blood on a specially prepared piece of blotting paper. As we know, a drop of water, or ink, or any liquid, deposited on blotting paper rapidly spreads out. Similarly, if a strip of blotting paper is dipped in a liquid, the liquid rises, in the same way that the oil in  a lamp rises in the wick, to burn steadily. Now, it is also a fact that different substances dissolved in the liquid rise along with the liquid at different rates.

This means that if the liquid contains different substances, the substances would get separated, as the faster ones spread out, while the slower ones stay back. This property, in fact is actively used to identify the substances in a liquid, or to separate components of a liquid.

In the case of blood, too, the serum, which is mainly water, as well as the blood products, which are in suspension, spread out if deposited on blotting paper. But if the blotting paper is first treated with antibodies for different blood groups, then the red blood corpuscles of those blood groups would clump, and they would not spread.

This property, of some components not spreading, can be linked to a change in the colour of the paper strip, to act as a fast, inexpensive and permanently recorded test of the blood group. “The paper diagnostics manufacturing cost is a few pennies per test and can promote health in developing countries,” the authors of the Anal. Chem. report say.

(Published 05 July 2010, 12:17 IST)

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