Plasma viscosity: accuracy, precision and suitability – who wants it?

Since 1947, when John Harkness published his seminal work on clinical plasma viscosity (PV) analysis in the British Medical Journal, the test has been generally misunderstood and certainly underutilised. With the infection of humans by SARS-CoV-2 since late 2019, the pandemic has forced scientists to take a fresh and detailed look at infections and PV; not just PV per se, but its values, trends and the fact it can be used in the calculation of a possible predictor of severity. The world may well now see that Professor Harkness was a man before his time, and posthumously he will receive due recognition.

In May 2020, a paper published in The Lancet by a team at the Emory Medical Centre in Atlanta, Georgia, showed that COVID-19 patients who developed severe symptoms had markedly raised PV levels.¹ This raised the profile of the test among medical and scientific professionals trying to cope with the new pandemic.

During more than 70 years since Harkness’s work, there have been many publications confirming the clinical value of using PV for investigating patients with an acute-phase response or with paraproteins. In early publications plasma viscosity was compared against the established erythrocyte sedimentation rate (ESR), and later against both ESR and C-reactive protein (CRP). The PV test received favourable reports in many of the papers.