title: Whole blood viscosity issue VIII: Comparison of extrapolation method with diagnostic digital viscometer.
abstract: BACKGROUND
  The first issue of this series proposed extrapolation chart with conventional reference range and suggested comparison of results with other methods.
  
  
  OBJECTIVE
  This work sets out to compare interpretative results from the extrapolation method with those from a digital viscometer method.
  
  
  METHODS
  Five cases in our archived clinical pathology database that were specifically tested for whole blood viscosity by the digital method, and had results for haematocrit and serum proteins were pooled. The values of haematocrit and serum proteins were used to derive extrapolated values. The interpretative results of the extrapolation method were compared with those of digital viscometer-based clinical reports. Non-Newtonian fluids such as whole blood have different viscosities at different shear rates. Comparative statement can only be based on interpreted outcome.
  
  
  RESULTS
  Two-fifth absolute concordance and one-fifth discordance is observed between extrapolation and viscometer-based clinical reports. The discordance is a case of hyperviscosity in the presence of neither hyperproteinaemia nor polycythemia.
  
  
  CONCLUSIONS
  The extrapolation method may underestimate whole blood viscosity in some patients when compared with digital viscometer, which in turn may suggest hyperviscosity that cannot be explained by hyperproteinaemia or polycythemia concepts. The impact of oxidative stress is highlighted.
authors.affiliation: Nepean Hospital Pathology, Derby Street, Kingswood, NSW 2747, Australia.
authors.forename: Ezekiel Uba
authors.initials: EU
authors.lastname: Nwose
authors.forename: Ross Stuart
authors.initials: RS
authors.lastname: Richards