Definition

A blood viscosity test is a diagnostic procedure used to assess the viscosity, or thickness, of blood plasma, which is the liquid component of the blood. Blood viscosity is influenced by the concentration of proteins present in the bloodstream. Protein levels typically increase as a natural response to conditions such as infections or inflammation. In certain pathological conditions, blood viscosity rises due to the abnormal production of proteins known as paraproteins.

This test is considered part of the blood hemostasis evaluation. Monitoring blood viscosity can be instrumental in detecting and observing the progression of inflammation. For this reason, the blood viscosity test is sometimes referred to as an inflammation marker test.

Other tests that are commonly employed to measure inflammation include the erythrocyte sedimentation rate (ESR) and C-reactive protein levels. However, blood viscosity testing provides several benefits over ESR, despite being more complex to conduct and less frequently used.

Indication

A blood viscosity test is valuable for diagnosing various inflammatory conditions, including inflammation of the arteries (such as temporal arteritis or giant cell arteritis), and polymyalgia rheumatica (a condition characterized by inflammation in multiple muscle areas causing pain and stiffness).

Typically, your doctor may order a blood viscosity test, along with additional tests, when they suspect an inflammatory disease and observe symptoms that could indicate one of the aforementioned conditions. Symptoms to look for include:

• Persistent headache

• Pain in the neck, shoulder, or hip

• Stiffness in the joints

• Anemia, which is marked by pale skin and mucous membranes, fatigue, dizziness, and shortness of breath

• Unexplained weight loss

If your physician suspects an inflammatory disease, they may suggest this test to help with diagnosis and to monitor the disease's progression.

For individuals already diagnosed with conditions such as temporal arteritis, the blood viscosity test will be used periodically to track how the condition is evolving, as blood viscosity levels typically change over time with disease progression.

Apart from the aforementioned conditions, blood viscosity tests may also be conducted to help diagnose hyperviscosity syndrome. This condition is often tested in conjunction with an eye examination (fundoscopy). Hyperviscosity syndrome occurs when there is an excessive production of paraproteins, which thickens the blood, impeding its flow through the blood vessels. If left untreated, this can lead to reduced blood supply to vital organs, potentially resulting in severe complications.

Contraindication

There are no specific conditions that entirely contraindicate this test. However, certain situations may make it difficult to collect blood samples, such as the presence of infections in the arm, blood vessel grafts, bruises, or arteriosclerosis (hardening of the arteries). In such cases, blood sampling may be attempted from other body parts.

Preparation Before the Test

No special preparation is required prior to this test. The blood viscosity test can be performed without the need for fasting, and blood samples can be taken at any time of the day.

Test Procedure

A healthcare professional will collect a blood sample by inserting a small needle into a blood vessel. A small amount of blood will be drawn into a tube or vial. You may experience minor discomfort when the needle is inserted or removed, but this procedure typically lasts no longer than 5 minutes.

Normal and Abnormal Values

Blood viscosity is evaluated by determining the amount of force necessary to move blood plasma through a thin tube within a specified time frame. The normal range for blood viscosity is between 1.3 and 1.7 mPas (millipascal-seconds). The higher the viscosity value, the thicker the blood, indicating a higher resistance to flow.

Results and Recommendations (Follow-up Tests)

Blood viscosity test results can be assessed based on the extent of the increase in viscosity, which can be categorized as follows:

• A moderate increase in viscosity is typically seen in inflammatory conditions but may also be influenced by factors such as smoking.

• A significant increase in blood viscosity generally points to a specific cause, such as an infection. In these cases, additional tests, such as microbiological cultures, may be recommended depending on the symptoms presented.

• A very high increase in blood viscosity is uncommon in infections or inflammation but may indicate the presence of paraproteins, which are linked to certain cancers like myeloma or lymphoma. In such instances, further diagnostic tests will be necessary to confirm the condition.

In general, elevated blood viscosity is one of the key results used to confirm the presence of specific inflammatory diseases, such as temporal arteritis, giant cell arteritis, and polymyalgia rheumatica. Even when patients are undergoing anti-inflammatory drug therapy, blood viscosity remains elevated, whereas ESR levels may return to normal after treatment.

While the blood viscosity test serves as a non-specific marker of inflammation, it cannot definitively pinpoint the exact cause of the inflammation. Therefore, the results should be interpreted in conjunction with clinical symptoms, medical history, and other relevant lab results to determine the specific underlying condition causing the abnormal blood viscosity.

Additional tests that may be requested by your doctor to further investigate the cause of abnormal blood viscosity include C-reactive protein tests, a complete blood count, blood smear analysis, and other biochemical assessments. Based on your symptoms, your doctor might also recommend tests for autoimmune diseases, such as ANA (antinuclear antibody) or RF (rheumatoid factor), which are linked to conditions like lupus or rheumatoid arthritis. If an infection is suspected, bacterial cultures might also be ordered.

Before proceeding with more extensive investigations to determine the cause of the inflammation, your doctor may repeat the blood viscosity test after several weeks or months. In some cases, the exact cause of inflammation may remain unidentified, and the test results could normalize without intervention.

Consult the Right Doctor

If your blood viscosity test results are abnormal, it’s advisable to consult with a general practitioner. If an inflammatory disease is suspected, your doctor may refer you to a specialist, such as an internist, for further evaluation and treatment.

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