What is Plasma Therapy?

From the US to India, researchers across the Globe are racing to trial plasma therapy as a potential treatment for Covid-19 patients. Here we will explain what plasma therapy is, how it has been used before, and what the science says so far as to its use as a treatment against coronavirus.

What is Plasma? Convalescent plasma. Plasma is the largest component of blood, contributing 55% of our total blood volume. If you were to split the components of our blood apart (which is what they do to extract plasma, but we’ll talk about this later), plasma is a “clear” yellowish liquid which carries our platelets, red and white blood cells. Our plasma also contains over 700 proteins (such as enzymes) and other substances (such as water and salts), some of which we can utilise for those in need. Plasma is collected in one of two ways: by separating it out from regular blood donations, and from male A and AB type platelet donors (women don’t currently donate plasma – apart from for covid-19 trials – as they’re more likely to have antibodies in their plasma which are created against their baby’s blood during pregnancy).

blood composition

How is plasma useful in treatments? Donated plasma is usually frozen to preserve its quality and is referred to as FFP (fresh frozen plasma). FFP can be concentrated further making it rich in clotting factors (called cryoprecipitate), helping to clot blood in haemorrhaging patients. A less common use of plasma though, is for plasma therapy, utilising antibodies which are present in the plasma (or in posh scientific terms, immunoglobulins). The therapy uses antibodies found in the blood of people who have recovered from (or convalescedyou’ll see this written a lot when talking about plasma therapy and covid-19) an infection, to treat patients who are infected and need a helping hand to overcome the infection/disease. Immunoglobulins (antibodies) are critical in an immune response. They recognise and bind to things such as the spike proteins seen on the coronavirus, highlighting them as foreign bodies which need to be destroyed. Antibodies are produced by our white blood cells when infected by bacteria, viruses etc. and can be used to combat the disease/infection if we encounter it again in the future. Antibodies we have created will always be detectable in our blood, and therefore we can deduce if an individual has had a certain disease/infection before. Pharmaceutical company Roche, have had their antibody test (I’ll do another post about this – covid-19 is keeping me busy) given an emergency FDA approval and is under testing in the UK currently.


Could plasma therapy be used to treat covid-19? First things first, plasma therapy is not the same as a vaccination. Vaccinations are designed to prevent you from contracting a disease in the first place. Plasma therapy instead aims to kick-start an already infected patient’s body into producing its own antibodies; this is known as passive immunity. It is temporary but immediate. Theoretically this therapy can be used in patients with an immune system which is unable to fight the infection, making it an interesting point of research for covid-19. In March, China was first to report plasma therapy tests on 5 patients who had severe covid-19 symptoms and were ventilated. Within 12 days of receiving treatment, viral concentrations had dropped to zero and all patients recovered. However, these patients also received other antiviral drugs during this time, so the effectiveness of plasma therapy was questioned. Since then, the US has also been testing the therapy in over 1,500 hospitals, whilst the UK is preparing to start its own testing. The NHS is now collecting plasma from people who have recovered from covid-19 for use in plasma therapy clinical trials. The trials will investigate whether these plasma transfusions could improve a covid-19 patient’s speed of recovery and chances of survival. You can sign up to donate HERE.


However, plasma therapy is not new technology and has been in use since the 1800’s; first in diphtheria in 1892 and then scarlet fever in the 1920’s to name just two instances. The effective use of plasma therapy against viruses though is yet undecided. During the 1918 Spanish flu pandemic, plasma therapy was used with mixed results. However, it has been used with more success more recently to treat the Ebola virus. It is hoped these covid-19 plasma therapy trials will shed more light on the potential benefits of the therapy, and when is the most effective time to issue it as a treatment in infected patients. Plasma therapy however, does not come without its risks. As with any transfusion, there are associated risks such as an allergic reaction. Other complications were observed when plasma therapy was used to treat the dengue virus. Patients became much worse as the therapy caused the virus to replicate.

Currently plasma therapy is only being tested on the most critically ill covid-19 patients. There are many aspects which need to be confirmed before plasma therapy could be rolled out, ensuring there are no inadvertent infection risks, no enhancement of the infection and no further suppression of a patient’s immune system. Such therapies have been beneficial in the SARS 2002 outbreak (another coronavirus), resulting in earlier patient discharge when compared to those who did not receive the transfusion. The current clinical trials will shed light on the above, and if the results are positive, plasma therapy could ease the strain of critically ill patients on health services (for this strain of coronavirus – mutations may require new antibodies). We’ll keep you up to date with all coronavirus research here at A Short Scientist.

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