Blood Viscosity: The Test that can Save The World? -- MEDICA - World Forum for Medicine


Benson Viscometers Ltd.

Blood Viscosity: The Test that can Save The World?

2020 has been a strange year all round. An unknown virus, probably originating in a bat colony in central China, mutated to allow it to also infect humans. Within three months of the virus being identified as Corona Virus SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2), 90% of the world had shut down.

Health care systems within the developed world were stretched to the point of collapse, old people were left to die in several “civilised countries”; world travel was stopped; many countries borrowed or printed money several times their GDP and political leaders fell in to two camps. One set of world leaders went in to political denial, "we will carry on as normal",  "pandemics will not affect our modern nation"; the other set went in to meltdown and locked down their countries with severe long term financial consequences. Neither reaction has protected the health or wealth of their population. Whether health or wealth has been damaged the most is yet to be determined, and maybe over time it will turn out that there is truly little difference.

Whatever the political reaction has been to the virus infecting their country’s population, the majority of leaders appeared to believe that medical science was going to miraculously save them from a problem over which they had neither knowledge nor control.

The overriding mantra was "our scientists will soon produce a vaccine which will save our population and our political skins"; meanwhile the virus, oblivious to the turmoil, marched on. Countries that had hoped to carry on regardless, soon found that they had a mounting death toll that they were being blamed for by not locking down effectively.

Those countries that had locked down rapidly, quickly realised that they had no way of maintaining lockdown either physically, or financially, until such time as a vaccine becomes available. Moving out of lockdown is proving to be a lot more difficult than imposing it in the first instance.

At the time of writing there is a realisation that the virus, or rather the disease caused by the virus, Covid-19, is here to stay, and we need to learn how to live with it.

Over the last 4 or 5 months, world scientists have collaborated to such an extent that, whereas 6 months ago, no one had heard of SARS- CoV- 2 or Covid-19, they now know its full genome, and how it can infect the human body. They also know that unlike any other Severe Acute Respiratory Syndrome, SARS- CoV- 2 does not produce a pure respiratory illness.

 In fact, most deaths attributed to Covid-19 are not respiratory but predominantly due to organ failure. A major contributing factor to this is the increased tendency for blood clots to form which leads to heart failure, strokes, kidney failure and when formed in the lung, respiratory failure. In short, the sickest Covid-19 patients suffer from multi organ failure.

Medical teams treating Covid-19 patients have faced a dilemma. For some time, it has been known that the majority of patients who contract Covid-19 infections do not develop a severe illness. However, the minority who do are strongly linked with other factors that increase the risk of ill health, such as being older, having heart or respiratory problems, having diabetes or being obese. Despite knowing these risk factors, there is no indication whether an individual patient will go on to develop severe symptoms. Medics around the world do not know which patients to monitor or treat until it is too late, by which time, the patient already has a severe condition which is extremely difficult to treat, and even if successfully treated, may leave them with long lasting health issues requiring long term support.

Now, what would the medics around the world say if there was a cheap simple blood test that could divide these patients in to the two groups, those that need treatment and those that don’t?

This is where clinical viscosity measurements come in. Clinical viscosity measurements have been reported in literature for over 100 years and easy to use analysers have been available for 50 years. Full clinical blood viscosity analysis requires 3 distinct analyses: -

Whole blood viscosity

      Whole blood viscosity measures a sample of blood containing all the fluid and cellular constituents. The main factor affecting blood viscosity is the red cells, both their volume, usually taken as the haematocrit, and their ability to change shape.

Plasma viscosity

      Plasma viscosity measures the viscosity of blood fluid with all the cellular components removed. The key factors affecting plasma viscosity are the fibrinogen concentration and antibody levels. More of which later.

Serum viscosity

      Serum viscosity measure blood fluid after the blood has clotted and therefore does not contain several of the factors required in blood clotting, of which fibrinogen is one. Therefore, the main factor to affect serum viscosity is antibody concentration.

In current practice whole blood viscosity measurements are time consuming and difficult to perform.  Many analysers require measurements at varying shear rates on the same sample. Fortunately, in Covid-19 patients, the most valuable information is obtained from plasma and serum viscosity analysis.

There are numerous reports that severe Covid-19 patients have raised blood viscosity levels. More significantly, these patients have raised plasma and serum viscosity levels.

A paper published by Emory University; Georgia Atlanta in the Lancet 25 May 2020 by Cheryl Maier demonstrated a dramatic rise in severe Covid-19 patients of more than double the normal value. This paper also linked the rise in viscosity to patients with severe clotting risks.

An understanding of what is being measured in plasma viscosity makes this link an obvious one. As mentioned earlier in this article, plasma viscosity is mainly affected by fibrinogen and antibody concentrations in the patient. Fibrinogen is the compound that is the precursor to the fibrin strands that form a blood clot. In normal human blood it is found at a concentration of 1.5 to 4.0 gms/l. In Dr Maiers Covid-19 patients she found they had fibrinogen levels of up to 5 times the normal value. It could therefore be inferred that patients with a high or rising plasma viscosity are the patients that are going to have or develop severe multi organ failure. Unfortunately, as with most aspects of the Covid -19 infection, things are not that simple.

Both fibrinogen and antibody levels affect the plasma viscosity so, a raised plasma viscosity cannot be attributed to fibrinogen concentrations without further testing. Although this is possible, fibrinogen analysis requires further blood samples to be taken and is a relatively expensive test. This is where a simple, cost-effective serum viscosity test comes in.

Serum viscosity is not affected by fibrinogen levels but is affected by antibody levels. Therefore, if a plasma and a serum viscosity analysis is performed on blood from a Covid-19 patient, drawn at the same time, it is possible to extrapolate meaningful clinical data by comparing the two results.

It is unusual to have reduced values of either plasma or serum viscosity.

Logically patients can have: -

Plasma viscosity raised with a normal serum viscosity

A raised plasma viscosity with normal serum viscosity indicates a raised fibrinogen concentration with no active antibody response present. These patients are probably deteriorating and will therefore be more likely to require intensive therapy.

Plasma viscosity and serum viscosity results both raised

If the plasma and serum viscosity analysis reveal that both results are raised, then the patient has raised antibody levels, and may also have a raised fibrinogen concentration.

These patients should have their fibrinogen concentration levels monitored to see if it is rising or falling. Rising levels of fibrinogen are indicative of the patient deteriorating. Falling levels could indicate that the patient may be recovering.

In either scenario, further observation and investigation of fibrinogen levels will be required.

Plasma viscosity and serum viscosity results both normal

If an individual has a positive Covid test result where both plasma and serum viscosity results are normal, they are probably asymptomatic but potentially a carrier.

Plasma viscosity normal with serum viscosity raised

This scenario is unlikely to occur because the proteins found in serum are also found in plasma. Therefore, a raise in serum viscosity would result in a raise in plasma viscosity.

In conclusion these simple cost-effective tests could well be the way of leading the world out of the dilemma posed by SARS-CoV-2. At least until that elusive vaccine is available.




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