Introduction to Viscosity Serum Tests
Viscosity is a measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid. Viscosity testing allows manufacturers to characterize the flow properties of various liquids and semi-solids. This is an essential quality control test for products like sauces, lotions, polymers, oils, and more.
One common viscosity test method is the serum viscosity test. This test measures a serum's viscosity at different shear rates and temperatures. Serum is the clear, straw-colored liquid portion of blood plasma. Measuring serum viscosity provides insights into a person's health status.
This article provides an overview of serum viscosity testing. It covers:
- What is serum viscosity?
- Why test serum viscosity?
- Normal serum viscosity levels
- How to measure serum viscosity
- Factors that affect serum viscosity
- High and low serum viscosity
- Conditions associated with abnormal serum viscosity
- Limitations of the test
What is Serum Viscosity?
Serum viscosity measures a serum sample's resistance to flow under an applied force. It depends on the serum proteins and other solutes present. Normal serum is slightly viscous compared to water.
Serum contains over 100 different proteins. The most abundant are albumin, globulins, and fibrinogen. These proteins mainly determine serum viscosity.
- Albumin is small and negatively charged. It decreases viscosity.
- Globulins are large proteins that increase viscosity.
- Fibrinogen forms long fibrous strands that make serum more viscous.
A higher protein concentration increases serum viscosity. Changes in individual proteins also alter viscosity. Specific proteins becoming elevated or depleted can make serum more or less viscous.
Why Test Serum Viscosity?
Measuring serum viscosity aids clinical diagnosis in several ways:
- Monitors general health status - Abnormal serum viscosity often indicates an underlying health condition.
- Screens for inflammatory conditions - Inflammation alters serum protein composition and increases viscosity.
- Assesses liver disease - Low albumin and high globulins in liver disorders increase viscosity.
- Evaluates blood disorders - High fibrinogen in conditions like myeloma makes serum more viscous.
- Monitors monoclonal gammopathies - Spike in abnormal immunoglobulins increases viscosity.
Quick and easy to perform, serum viscosity can provide a snapshot of a person's overall health. It may prompt further testing to investigate any suspected conditions. Monitoring serum viscosity over time also helps assess disease progression and treatment efficacy.
Normal Serum Viscosity Levels
Normal serum viscosity ranges between 1.4-1.8 mPa.s or centipoise (cP) at 37C. It does not usually exceed 1.9 mPa.s.
Serum viscosity depends on the measurement technique used. Different methods give slightly different reference ranges. Normal values also go up as people age.
A serum sample's viscosity is often compared against water's viscosity. At 37C, water has a viscosity of 0.695 mPa.s. So normal serum is around 2-2.5 times more viscous than water.
How to Measure Serum Viscosity
Specialized instruments called viscometers measure serum viscosity. There are several viscosity measurement methods:
- Capillary viscometers - Measure flow time through a glass capillary tube.
- Falling ball viscometers - Measure rolling time of a ball bearing through the serum.
- Vibrational viscometers - Measure damping of an oscillating sensor in the serum.
- Rotational viscometers - Measure torque required to rotate an immersed element.
Of these, automated capillary viscometers are most common. They allow rapid analysis of the small serum volumes available.
Viscometers test serum viscosity at different shear rates. Shear rate is the velocity gradient perpendicular to fluid flow direction. It represents how fast the serum flows during testing.
Serum viscosity decreases at higher shear rates due to shear thinning. Results are usually reported at a standard low and high shear rate:
- Low shear - Around 5 s-1
- High shear - Around 200 s-1
Factors Affecting Serum Viscosity
Many analytical and physiological factors influence serum viscosity test results:
- Temperature - Serum viscosity decreases as temperature rises. Samples should be tested at 37C.
- Plasma proteins - Increased globulins and fibrinogen increase viscosity.
- Serum lipids - Elevated lipids like cholesterol and triglycerides increase viscosity.
- Albumin - Low albumin levels increase viscosity.
- Hematocrit - Higher red blood cell percentage increases viscosity.
- Hydration status - Dehydration increases serum viscosity.
Factors like diet, hormones, inflammation, blood disorders, and liver disease alter serum protein composition. This indirectly changes viscosity.
High and Low Serum Viscosity
Increased or decreased serum viscosity can indicate specific medical conditions:
High Serum Viscosity
Serum viscosity above 1.9-2.0 mPa.s is considered abnormally high. Possible causes include:
- Inflammation (e.g. infections, arthritis, vasculitis)
- Cancer (e.g. lymphoma, multiple myeloma)
- Liver disease (e.g. hepatitis, cirrhosis)
- Metabolic syndrome
- Diabetes
- Hyperlipidemia
- Kidney disease
- Dehydration
Low Serum Viscosity
Serum viscosity below 1.4-1.5 mPa.s may indicate:
- Decreased globulins (e.g. liver disease, kidney disorder, protein loss)
- Low fibrinogen (e.g. liver disease)
- Hyperalbuminemia
- Multiple myeloma
- Lymphoma
Increased plasma dilution due to intravenous fluid therapy or hypervolemia also decreases viscosity.
Conditions Associated with Abnormal Viscosity
Some key conditions linked to altered serum viscosity include:
Chronic Inflammation
Inflammation increases fibrinogen and large globulins in serum. Rheumatoid arthritis, lupus, vasculitis, and infections like HIV/AIDS often show elevated viscosity.
Multiple Myeloma
Myeloma causes proliferation of abnormal immunoglobulins called M proteins. These increase serum viscosity substantially at both high and low shear rates.
Waldenstrom Macroglobulinemia
This disorder features high levels of large IgM antibodies. Hyperviscosity syndrome with symptoms like nosebleeds, vision issues, and headaches can occur.
Cryoglobulinemia
Certain immunoglobulins become insoluble at low temperatures. Cryoglobulins precipitate and make serum highly viscous during viscosity testing.
<h3FAQs
What is the normal range for serum viscosity?
The normal range is between 1.4-1.8 mPa.s or centipoise (cP) at 37°C. Serum viscosity up to 1.9 mPa.s is usually considered normal.
How is serum viscosity measured?
Specialized instruments called viscometers are used. Capillary viscometers that measure flow time are most common. Other types include falling ball, vibrational, and rotational viscometers.
What medical conditions increase serum viscosity?
Conditions that increase large proteins like fibrinogen and globulins tend to increase serum viscosity. These include inflammation, multiple myeloma, liver disease, diabetes, and metabolic syndrome.
What factors decrease serum viscosity?
Low albumin, intravenous fluids, hypervolemia, decreased globulins from liver/kidney disease, lymphoma, and multiple myeloma can reduce serum viscosity.
Why test serum viscosity in medical diagnostics?
Serum viscosity provides clues about overall health status. It is used to screen for inflammatory conditions, monitor blood disorders, assess liver disease progression, and evaluate treatment efficacy.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.
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