BLOOD SCIENCES


a patient with normal results: plasma viscosity is about 1.60 mPa.s; while the corresponding serum viscosity is typically 1.50 mPa.s, when measured at 37°C and reported at 25°C. It reflects the fact that plasma contains fibrinogen and other cloting factors, while serum does not. The PV:SV ratio will determine which of the protein fractions actually contribute to the abnormal viscosity of the patient sample. As the patient plasma sample contains


the acute phase protein fibrinogen and other cloting factors, the viscosity of plasma increases earlier in the disease state and strongly in infections, inflammation, auto immune flare and tissue injury. In paraproteinemias involving IgM, IgA, or IgG, serum viscosity serves as an excellent diagnostic indicator. It should be noted that the presence of paraproteins influences both serum and plasma viscosity.


The PV and SV ratio can distinguish and clarify whether the infection or inflammation is significant in comparison to elevated immunoglobulins and hyperviscosity. For example, a high PV with a normal


SV is likely caused by increased plasma protein and fibrinogen levels, as seen in infection or inflammation. If both PV and SV are elevated, hyperviscosity is likely due to increased immunoglobulins, as seen in conditions such as Waldenström’s macroglobulinemia or multiple myeloma. These conditions are often first suspected with a raised PV, which usually triggers further investigations such as quantitative serum electrophoresis. However, a PV:SV


Feature Sample type Recommended use Influencing factors Value when diagnosing


paraproteinaemia IgM / IgG / IgA Use in hyperviscosity syndrome


A recommendation


for plasmapheresis Clinical application


Current usage and popularity


It is clear that the PV:SV ratio has extensive diagnostic and monitoring potential in many


complex disease states, with particular relevance for chronic inflammatory conditions


ratio can be established easily and quickly to support the later findings. The advantages of the PV:SV ratio was proven in the 1981 study20


by Alexander et


al. The study explored whether measuring both plasma viscosity and serum viscosity could beter predict which patients with early rheumatic symptoms would later develop chronic arthritis. The researchers compared plasma and serum viscosity in 115 patients who had recent-onset symptoms and were followed for at least six months. The study found that while many patients had raised plasma viscosity, only those with raised serum viscosity were very likely to develop chronic arthritis. Specifically, 28 of 29 patients with high serum viscosity later developed chronic arthritis, showing that serum viscosity was a strong predictor. Overall, the study suggests that combined PV and SV testing will identify earlier which patients with acute rheumatic symptoms are at risk of progressing to chronic disease. Therefore, the PV:SV ratio is clinically


valuable for distinguishing, identifying and monitoring the following:21


Plasma Viscosity (PV)


Plasma, contains fibrinogen, and other cloting factors.


For infection, inflammation and traumatic injury.


Plasma includes fibrinogen. Excellent. Very good screening. Very helpful.


Helps to isolate acute phase protein and paraprotein effects.


United Kingdom and Europe.


The plasma to serum viscosity (PV:SV) ratio. April 2026 WWW.PATHOLOGYINPRACTICE.COM 19 Serum Viscosity (SV)


Serum, absence of fibrinogen with no cloting factors.


For paraprotein-related hyperviscosity.


No fibrinogen, and no cloting factors.


Excellent – SV directly reflects the presence of paraproteins.


Benchmark for monoclonal IgM hyperviscosity.


Extremely helpful.


Helps to isolate paraprotein effects.


Primarily USA.


inflammatory elevation (plasma > serum) paraprotein-related hyperviscosity hyperviscosity syndromes and inflammatory conditions.


Advantages of PV and SV testing Clinical viscosity measurements provide significant advantages22


when


compared with other laboratory assays for the identification of infection and inflammation, as follows: same reference range for all ages, (over three years old) same reference range for both genders unaffected by physiological stimuli: lifestyle, smoking, body weight, and blood pressure unaffected by anaemia and polycythaemia aspirin and steroids do not interfere or distort the plasma and serum viscosity results tests can be performed on a plasma sample up to seven days and on a serum sample up to 14 days old myeloma, Waldenström’s macroglobulinaemia and


Plasma:Serum Ratio (PV:SV) The PV:SV ratio is diagnostically fundamental.


PV increases with inflammation. SV rises with paraproteinaemia.


Differentiating between inflammation or paraproteinemia.


Due to the presence of fibrinogen, PV is a superior test for the detection of infection and inflammation.


Increase in PV and SV levels may well indicate paraproteinemia.


Can confirm paraproteinaemia as the main cause. PV:SV ratio strengthens decision-making. PV:SV ratio may aid in a differential diagnosis. The PV:SV ratio can distinguish between


inflammation and paraproteinaemia. Both PV and SV should be used globally.


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