Frequently asked questions

Plasma viscosity (PV) gives a measure of the acute phase response, which will increase as part of the body’s normal response to infection, inflammation and traumatic injury. The viscosity of plasma influences and changes in proportion to the quantity and molecular size of plasma proteins, particularly fibrinogen, immunoglobulins and paraproteins.

Therefore, changes in plasma viscosity correlate directly with disease severity and response to treatment. PV is a superior inflammation marker compared to ESR and CRP tests.

Plasma viscosity is widely used by scientists and clinicians in diagnosing and monitoring a host of complex clinical conditions. Most commonly:

• Multiple myeloma
• Waldenström’s macroglobulinaemia
• Hyperviscosity syndrome
• Temporal arteritis
• Polymyalgia rheumatica
• Rheumatoid arthritis
• Cardiovascular disease
• Other infection and inflammatory conditions

PV 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 to two decimal places.

The PV normal reference range for individuals aged 3 years and above is:

• 1.12 to 1.27 mPa.s or cP, tested and reported at 37°C
• 1.50 to 1.72 mPa.s or cP, tested at 37°C and reported at 25°C, room temperature

Importantly, a minor variation in a patient’s PV of 0.05 mPa.s is deemed to have clinical significance. The viscosity units are expressed in mPa.s (millipascal-seconds) or centipoise (cP). The PV reported value is identical whether expressed in mPa.s or cP.

If PV is slightly above the laboratory’s upper limit, it can be consistent with a relatively minor or temporary inflammatory response. A more substantially or persistently elevated result may prompt further investigations.

Common reasons for a raised PV:

• Infection, including a recent or ongoing infection
• Inflammation, such as rheumatoid arthritis or other inflammatory or autoimmune conditions
• Tissue injury or trauma
• Polymyalgia rheumatica or temporal (giant cell) arteritis
• Increased immunoglobulins (antibodies)

High to very high PV is commonly seen in conditions such as multiple myeloma, Waldenström’s macroglobulinaemia and hyperviscosity syndrome.

A high PV does not by itself diagnose any of these conditions. The degree of elevation, symptoms and other blood results are important factors.

The viscosity of plasma is influenced by the quantity and molecular size of plasma proteins, particularly fibrinogen, immunoglobulins and paraproteins, which will increase as part of the body’s normal response to infection, inflammation and traumatic injury.

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 several haematological conditions.

PV rises when there are increased plasma proteins, particularly fibrinogen, immunoglobulins or abnormal proteins (paraproteins). Cancer is one possible cause, but infection and ordinary inflammation are much more common explanations.

Certain blood cancers can cause a particularly high PV, including:

• Multiple myeloma
• Waldenström’s macroglobulinaemia

Importantly, the level and persistence of the elevation matter. PV needs to be interpreted alongside symptoms and other blood tests.

A high plasma viscosity (PV) is generally considered a marker of an underlying pathological process rather than a harmful condition in itself.

PV can rise in relatively common conditions such as:

• A recent or current infection
• Inflammation
• An autoimmune or inflammatory condition
• Increased blood proteins such as immunoglobulins

A very high PV can occasionally occur when there are large amounts of abnormal proteins in the blood, which can make the blood abnormally thick (hyperviscosity syndrome). Waldenström’s macroglobulinaemia and multiple myeloma are the common causes of hyperviscosity syndrome.

The important things to consider are how high the viscosity result is, whether it remains elevated, and why it is elevated. A small elevation is often not dangerous, particularly if the patient has an obvious infection or inflammatory illness.

A slightly raised or borderline plasma viscosity (PV) result usually indicates a mild increase in plasma proteins associated with inflammation. It is a non-specific finding and, on its own, does not indicate a particular disease.

Common explanations include:

• A recent or mild infection, even if the patient is recovering and feeling better
• Low-grade inflammation, including inflammatory or autoimmune conditions
• Temporary changes in plasma proteins, particularly fibrinogen and immunoglobulins
• Less commonly, an increase in abnormal proteins (paraproteins)

A borderline result is generally much less concerning than a markedly elevated or persistently increasing PV. It is typically interpreted alongside symptoms and other blood tests.

A low plasma viscosity (PV) means that the plasma is slightly less resistant to flow than expected. Low plasma viscosity is rarely of clinical significance. It may be observed in infants, particularly those younger than three months, and in individuals with reduced levels of plasma proteins such as fibrinogen or immunoglobulins. This may occur in conditions associated with impaired protein synthesis, such as some liver disorders, or following substantial blood transfusion. An isolated, mildly reduced plasma viscosity result is not usually clinically significant; however, it should be interpreted in conjunction with the patient’s clinical presentation and other laboratory findings.

A slightly elevated PV can occur with a recent infection or inflammation and may return to normal as the underlying problem resolves. There is no specific food, supplement or exercise routine proven to directly lower PV.

If the PV is markedly elevated, particularly alongside symptoms such as headache, blurred vision, dizziness, confusion, unusual bleeding or shortness of breath, medical assessment is important.

Hyperviscosity syndrome (HVS) is a medical condition that requires urgent and prompt medical assessment, particularly when it is caused by excess abnormal proteins in the blood. Treatment depends on the underlying cause.

How is it treated?

• Plasma exchange (plasmapheresis) is the main emergency treatment when HVS is caused by excess immunoglobulins, particularly in conditions such as Waldenström’s macroglobulinaemia. It rapidly removes the excess proteins from the plasma and can improve neurological and bleeding symptoms.
• Treatment of the underlying disease is then required to prevent the hyperviscosity from returning. Depending on the cause, this may involve chemotherapy, targeted therapy, immunotherapy or other treatments.
• Fluids and supportive treatment may also be given, depending on the patient’s condition. Treatment needs to be supervised in a hospital setting.

A standard blood sample is taken from a vein and the blood is collected into an EDTA tube (usually a lavender or purple-top tube). The laboratory separates the plasma using a centrifuge according to their standard operating procedure. The separated plasma sits at the top of the red blood cells in the test tube. After centrifugation, PV tests using a Benson Clinical Viscometer can be reported in under one minute.

Both plasma viscosity (PV) and ESR (erythrocyte sedimentation rate) are blood tests that can indicate inflammation, but they measure it in different ways.

Our comparative review of plasma viscosity, ESR and CRP is on the support literature page.

Both plasma viscosity (PV) and CRP (C-reactive protein) are blood tests that can indicate inflammation, but they measure it in different ways.

CRP is a single protein made by the liver that rises within hours of an infection and falls quickly once it clears, so it is the better test for acute infection and for checking a treatment is working day to day.

Plasma viscosity (PV) gives a measure of the acute phase response, which will increase as part of the body’s normal response to infection, inflammation and traumatic injury. Therefore, PV has a role in diagnosis, disease progression and treatment monitoring.

Our comparative review of plasma viscosity, ESR and CRP is on the support literature page.

Plasma viscosity (PV) is unaffected by anaemia, polycythaemia, age or sex. PV is also not significantly influenced by lifestyle factors such as smoking, body weight or blood pressure. Medications such as aspirin and steroids have no significant effect. A PV result can be expected to be increased during the second and third trimesters of pregnancy, until term. This is due to the rise in fibrinogen concentration.

CRP: samples are often recommended to be centrifuged and separated within about 2 hours, mainly to preserve sample integrity and analytical accuracy.

ESR: keep as whole EDTA blood and analyse preferably within 4 hours of venepuncture.

PV: the EDTA patient blood sample is centrifuged at the earliest opportunity to separate the plasma from the haematocrit. Ideally, plasma viscosity testing should be completed within 24 hours. If immediate testing is not possible, the separated plasma can be transferred to a clean, sealed sample tube and stored for up to a maximum of 7 days prior to analysis at laboratory room temperature.