Storage of blood samples for measurement of plasma viscosity and erythrocyte sedimentation rate

Plasma viscosity is used as an alternative to the erythrocyte sedimentation rate (ESR) as a test of the acute-phase response. To determine the effect on these tests of delay between venepuncture and time of testing we have stored plasma and whole blood samples from 39 individuals for 7 days at both 4°C and room temperature (RT). Serial daily testing showed no significant change in the plasma viscosity of separated plasma stored at 4°C or RT or of whole blood stored at 4°C. Whole blood stored at room temperature was stable for 4 days. A closed-tube system was used to determine the stability of the ESR at 4°C, but there was still a progressive fall in the ESR value over 7 days of storage. This study confirms the validity of plasma viscosity measurements when there is a delay in separation of plasma and/or testing.