BLOOD SCIENCES


through well-established quality control and quality assurance schemes, notably at the United Kingdom, National External Quality Assessment Service, (UK NEQAS). PV has a very narrow, specific reference range and PV measures the overall collective effect of protein changes rather than a specific protein and offers several worthwhile advantages. These include that testing can be performed on a plasma sample up to seven days old, and the result is unaffected by factors such as anaemia, patient age, gender or smoking habit, while showing stronger correlation with disease activity. Also, PV results are not distorted or affected by medication such as salicylates (aspirin) or steroids, and test is independent of the haematocrit.27-30


Moreover, the


Clinical viscometers can measure the viscosity of human biological fluids: blood plasma, blood serum, whole blood and synovial fluid and will test directly from primary blood sample tubes.


is considered to be, a result within 1.50 - 1.72 mPa.s15


temperature) and 1.12 - 1.27 mPa.s reported at 37°C. Importantly minor variation in a patients PV of 0.05 mPa.s is deemed to have clinical significance.


Discussion and conclusions Over the last 20 years it has been common for haematology and biochemistry laboratories to combine to form blood science departments. The traditional soft barriers have been breached, though dedicated specialist staff remain in their particular disciplines to maintain service quality and expertise. These changes have seen the emergence of the managed service plan (MSP) for lease and maintenance of all major equipment and reagents, often over both disciplines, using a single combined contract.


Many of the major biochemistry analyser manufacturers incorporate CRP testing within their devices, subsidising the relatively expensive assay from the cheaper and more frequently requested tests such as urea and electrolytes, thus increasing its attraction to the customer when operating within a tight financial budget and considering an MSP. Some laboratories have retained their historical traditional discipline-specific inflammatory markers, offering two inflammatory tests, whilst others have made the difficult decision to provide just one. Hence it is not uncommon for some blood sciences laboratories to offer ESR or PV from haematology and CRP from biochemistry, whilst some only rely on a single marker.


Whilst an accurate direct conversion reported at 25°C (room


factor between any two or all three test methods cannot be produced due to variations and specificity, it can be seen from the evidence in this review that CRP appears to have some virtues, particularly its use as a predictor of cardiovascular disease and its point-of-care platform. However, it does have several considerable limitations. The numerous influences make the baseline figure less than certain which could impact on clinical decision making. Furthermore, there is a significant unclear (grey) area in results and interpretation. Whilst the ESR has earned its place


in history, the numerous limitations and interfering factors appear to make it an anachronism in the modern laboratory. Whilst a grossly raised ESR may be a good indicator of disease, particularly at the diagnostic stage, the tendency for the ESR to incorrectly report as ‘normal’ puts in to question the true value of the ESR test. When looked at objectively the ESR is unphysiological and does not reflect any part of the in-vivo circulation. Additionally, there are no realistic quality control or quality assurance schemes which accurately reflect the test conditions. Furthermore, in cases of IgG myeloma,


the ESR result is dramatically clear but paradoxically in IgM myeloma or Waldenström’s macroglobulinaemia the result is commonly reporting in the normal range due to the plasma being too viscous for the haematocrit cells to fall through under the effect of gravity, even despite the dilution with trisodium citrate. The PV test is sensitive and is a true


reflection of the in vivo conditions. Additionally, it is meticulously regulated


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combination of PV and serum viscosity ratios has been used as a predictor of chronic arthritis in patients with early rheumatic disorders.31 Where laboratories offer two different inflammation markers for best clinical practice, then the evidence above would indicate CRP and PV as the prime choice due to the limitations of the ESR. All three markers are well known to increase in bacterial, viral infections, sepsis and temporal arteritis. However, caution must be exercised in the interpretation of CRP results where it conflicts with that of PV due to the limitations above. PV has fewer limitations, the test is quick, sensitive, reliable, and inexpensive. Both CRP and PV have been used as predictive indicators of cardiovascular disease in addition to their role as inflammation markers.


The changes which occur in the viscosity of the plasma in multiple disease states have often been described and compared. Notably, the UK government’s recently announced 10-year plan for the NHS places a large emphasis on further development of medical analytical technology.32 Where only a single inflammation marker is provided by the laboratory then evidence would indicate that PV is clearly likely to be the best choice due to its indisputable baseline and narrow range. PV is a sensitive test and a change as small as 0.05 mPa.s is considered to be diagnostically significant. There are fewer influencing factors than CRP and its versatility appears to be at least as wide, as supported by a plethora of publications in numerous disease states. Additionally, its use as a cardiovascular


risk predictor does not require a separate assay technique and can be performed from the same sample or residue of a routine full blood count. In summary, while the on-board CRP assay presents some attractions, the PV appears to excel


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