BLOOD SCIENCES
of their approximate 120-day lifespan. Their flexibility is due to their shape, high surface-area-to-volume ratio, structural membrane components, cytoskeleton, internal viscosity and intracellular calcium level. Hence the importance of red cell deformability in health and disease cannot be over emphasised as the function of every organ and tissue is dependent on this. Red cell deformability can be assessed by several methods: laser diffraction (ektacytometry), micropore filtration and calculation being the three most widely used. Laser diffraction requires a specialist standalone instrument and gives a pictorial representation of red cell elongation but does not lend itself to batch analysis such as that required in a diabetic clinic. Micropore filtration through polycarbonate filters with pores of 5µm has been used for several years. However, it requires red cells to be washed three times before analysis to remove any white cells, thus rendering the measurement open to criticism of being unphysiological. Furthermore, it does not lend itself to batch analysis and is therefore probably better suited to research studies rather than everyday use.
Red cell rigidity (the inverse of
deformability) can be calculated from whole blood viscosity, plasma viscosity and haematocrit using an equation by Dintenfass.28
The calculation was
later evaluated by Norcliffe and Brown (1988).29
One of the advantages
this calculation has over the other methods is that no additional specialist equipment is required so a result can be relatively easily obtained without incurring additional cost, and sequential batch analysis can be performed. It is a calculation of rigidity: so the higher the value the less deformable the cells are, and it has a further advantage of a narrow reference range. It is possible to measure plasma and whole blood viscosity on a clinical viscometer (BV200 and BV1) to obtain a red cell rigidity value.
Measurement of plasma viscosity Since the introduction of efficient measurement of plasma viscosity (Harkness, 1971), testing has been available in many haematology laboratories.30
Plasma viscosity is
renowned as a quick, inexpensive, non- specific test, but also capable of being a more accurate and useful screening test. The viscosity of plasma is determined by the quantity and size of the proteins.31 Notably the amount of fibrinogen
Since the introduction of efficient measurement of PV, testing has been available in many haematology laboratories.
and the size of the immunoglobulins in the blood which increase as part of the body’s normal auto-response to infection, inflammation, and the effects of traumatic injury. Plasma viscosity results are tested
and reported at 37°C but can also be reported at 25°C (room temperature). The results are presented in a clear, easy to interpret numerical format, displayed in two decimal places. Since the PV reported value is identical whether expressed in millipascal-seconds (mPa.s) or centipoise (cP), both units are universally recognised and easily understood.
The plasma viscosity normal reference range for individuals aged three years and above is considered to be a result within 1.50 - 1.72 mPa.s reported at 25°C and 1.12 - 1.27 mPa.s reported at 37°C.32
a patient’s PV of 0.05 mPa.s is deemed to have clinical significance. The serum viscosity normal reference range is a result within 1.40 - 1.60 mPa.s reported at 25°C and 1.09 - 1.23 mPa.s at 37°C.33 Based on scientific studies, the plasma viscosity test is shown to be a robust and reliable tool that provides valuable insight into a patient’s health, particularly in relation to hyperviscosity syndrome as well as inflammatory and
WWW.PATHOLOGYINPRACTICE.COM DECEMBER 2025 Importantly a minor variation in
several haematological conditions.34 The PV test has advantages in terms of
stability, direct measurement, and minimal external factor interference. This makes it a superior choice in detection of elevated proteins and abnormal paraproteins in hyperviscosity syndrome and many clinical scenarios. Therefore, the PV and SV tests have
greater validity when investigating hyperviscosity syndrome due to their superior accuracy and sensitivity when compared to the C-reactive protein (CRP) test and ESR.
Conclusions Hyperviscosity syndrome is a critical condition characterised by an elevated risk of both bleeding and thrombosis, along with various other complications. Consequently, it is crucial to establish an early diagnosis, classification, and the underlying cause as swiftly as possible. Both plasma and serum viscosity serve as a rapid method to confirm or exclude paraproteinaemia, thus playing a vital role. Clinical viscosity test results are reliable, repeatable, and reproducible. Furthermore, by measuring whole blood viscosity, the rigidity of red blood cells can be assessed, providing the clinician with additional insights into the patient’s true in vivo condition. This can
35
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
