Monitoring COVID-19 plasma viscosity

Benson Viscometers designs and manufactures clinical viscometers to measure the viscosity (or thickness) of bodily fluids, notably blood plasma, serum, blood and synovial fluid. They are in use in UK NHS, Ireland and USA pathology laboratories.

The clinical viscosity test measures the thickness or resistance to flow of biological fluids, enabling clinicians to identify where a patient’s viscosity values are not within the recognised normal range.

The plasma viscosity test looks for abnormal concentrations of proteins in the blood plasma and is highly regarded as an important aid to diagnosis for a range of conditions, such as rheumatoid arthritis, myeloma and Waldenstrom macroglobuinaemia.

Plasma hyperviscosity is a known risk-factor for thrombosis and can be caused by increased levels of plasma proteins, such as fibrinogen or immunoglobulins. The serum viscosity test is used to monitor patients and assess hyperviscosity syndrome including polycythemia, macroglobulinemia, multiple myeloma, and leukaemia. Increased blood viscosity is an indicator for potential stroke and heart attack induced by a low flow of blood in the capillaries leading to an inadequate delivery of vital oxygen and nutrients to body tissues. Physicians in California are researching blood viscosity and its effects on cardiovascular disease.

Clinical viscosity for COVID-19 testing

Clinical viscosity testing, particularly plasma and blood, has now been identified by scientists as important in monitoring critically ill COVID-19 patients. A paper in The Lancet on May 25 associated very high plasma viscosity in critically ill COVID-19 patients with thrombotic complications and abnormal blood coagulation.

In COVID-19 patients, a rise in plasma viscosity is due to an increased concentration of a clotting (coagulation) protein called fibrinogen. This raised level of fibrinogen increases the risk of a blood clot forming (thrombosis) and could explain why a large proportion of the deaths from COVID-19 are from thrombotic episodes and not from pulmonary disorders, which would be expected from a virus that infects the respiratory tract.

Emory University researchers in Atlanta, Georgia, found that patients had substantially increased fibrinogen concentrations (an average of 708 mg/dL versus a normal reference range of 200-393 mg/dL). An article in Newsweek on May 28 further explored this study and the links between an increased abnormal plasma viscosity and COVID-19.

Critically ill COVID-19 patients being given drugs to reduce the likelihood of unwanted clot formation, had plasma viscosity levels 95 percent higher than normal, and more than 25 percent had blood clot-related complications.  The researchers also found a strong correlation between plasma viscosity levels and the severity of the patients’ illness, using the Sequential Organ Failure Assessment Score.  This revealed ‘substantially increased’ fibrinogen levels in the blood plasma.

UK COVID-19 diagnostics and prognostics

Several UK hospitals at the forefront of the fight against COVID-19, including Addenbrooke's Hospital Cambridge, University College London Hospital and St Thomas's in London, are currently conducting research to scientifically document the benefits of measuring plasma viscosity in COVID-19 patients.

Research is being carried out to explore the potential for plasma viscosity results to aid early identification of COVID-19 patients who are likely to develop more severe symptoms. Some UK hospitals have reported that early indications show a statistical difference between the COVID and non-COVID groups and the plasma viscosity test is routinely being performed to monitor COVID-19 patients.

Daniel Gleghorn, a senior scientist at Cambridge University Hospital NHS Foundation Trust, said: “We are in the process of establishing the diagnostic and prognostic value of measuring the plasma viscosity of patients, with a cohort of around 500 patients, following patients’ progress through the condition, regularly monitoring their plasma viscosity level.”

Paul Woods, a former pathology laboratory manager at Nobles Hospital in the Isle of Man, said: "Some laboratory tests are being utilised by the emergency department in relation to COVID-19 particularly d-dimer and ferritin.  These tests are also being used to monitor patients who appear to be deteriorating and may be in need of more intensive care. The laboratory also facilitated plasma viscosity availability 24/7 in relevant COVID-19 cases, which is notable, given it is not normally an out of hours test."

Deepak Singh, Head of Department, Haematosis, at Health Service Laboratories (a partnership between The Doctors Laboratory, Royal Free London NHS Foundation Trust and University College London Hospitals NHS Foundation Trust) said: “We are running plasma viscosity now to monitor inflammatory status in the following patient groups: Those with high risk TIA (transient ischaemic attack) commenced on DAPT (dual antiplatelet therapy); Those with treatment failure on antiplatelet therapy; Those with high risk carotid/vertebral or intracranial stenosis. This is to ensure antiplatelet drug therapy efficacy.”

Discussions are taking place with laboratories all around the world about how the role of routine plasma, blood and serum viscosity monitoring contributes to the understanding of COVID-19 progression. It is believed this will help to develop a more scientifically targeted treatment for patients producing improved recovery outcomes as a result.

Plasma viscosity test benefits

Benson Viscometers, based in Haverfordwest, is the UK market leader for clinical viscometers. Their viscometers are considered safe to use with high risk samples and incorporate ‘closed vial’ sampling in their operation. When laboratory staff are processing high risk samples, such as COVID-19, direct exposure to the biological fluid is minimised as the sample tube cap does not need to be removed for the sample to be tested.

Clinical viscosity diagnostic tests are efficient as they can be carried out using the residue from the full blood count analysis.  Plasma viscosity results are rapid, precise, and are not affected by variations such as gender, age, early pregnancy, or the presence of other conditions, such as anaemia. An advantage of the plasma viscosity test is that it will continue to give clinically significant results up to seven days after the sample has been taken. More importantly, the results are not altered or interfered with by the patient having taken medication such as high dose steroids, cytotoxic drugs and aspirin.

The creator of the Benson clinical viscometers, Bernie Benson, said: "I am extremely excited and encouraged by the passion and enthusiasm of so many scientists around the world as they work together to determine an understanding of the mysteries of COVID-19. We have always believed that clinical viscosity testing, and plasma viscosity testing in particular, has so much more to offer our healthcare system. I am confident pathology laboratories will invest the time and energy in this research and find the significant breakthrough in outcomes for critically ill patients and that the world is now waking up to the huge value of this clinical viscosity testing in general."