RA latex turbid test: What to know
Results outside of the normal range may be a sign of an underlying condition, but the rheumatoid arthritis (RA) latex turbid test is just one part of a thorough diagnosis.
In this article, learn more about the RA latex turbid test, including what causes abnormal levels.
What is an RA latex turbid test?
The RA latex turbid test is a type of blood test.
The RA latex turbid test is a diagnostic tool that looks for specific antibodies that are commonly present in people with RA.
RA is a chronic inflammatory autoimmune disease that targets the joints, causing inflammation. RA typically leads to pain, stiffness, loss of mobility, and in some cases, joint damage. In more severe cases, RA may cause deformities in the joints.
An autoimmune condition means that a person's immune system mistakenly attacks healthy tissue. In people with RA, the immune system typically attacks the joints, but it can also affect other organs.
When a person has RA, their blood will contain specific antibodies that help doctors make a diagnosis. One of the antibodies typically associated with RA is rheumatoid factor (RF). Testing for these antibodies is often an important part of diagnosing whether a person has RA.
The RA latex turbid test is relatively simple. A doctor will take a blood sample from the person's vein, which they send to a lab for testing.
They may take more than one blood sample if they will be performing other tests.
Technicians at a lab will test the blood using a small latex bead, which has an RF-specific antibody attached to it. When the antibodies on the beads find RF in the blood sample, they bind with it.
This process causes a noticeable change in the amount of light that can travel through the particles. Technicians look for this change, which they call turbidity.
This high turbidity identifies the RF antibody in the person's blood.
Sometimes, a person with RA does not test positive for RF. In these situations, a doctor will perform additional tests, including imaging studies, to help them make a diagnosis. People with Sjogren's syndrome or Hepatitis C may also have RF in their blood.
Normal range and results
A lab will analyze the blood sample to measure RF levels.
Generally, scientists consider RF levels of under 20 units per milliliter (u/ml) as normal. However, the typical range varies slightly from lab to lab.
Anything higher than 20 u/ml may indicate the presence of antibodies that are a sign of autoimmune conditions, such as RA.
In general, the higher the values, the more likely it is that the person has an underlying condition.
According to HSS, 20% of people with RA do not have elevated RF values. Also, about 5% of people who do not have RA will have abnormal RF test results, usually due to another condition.
If a person's test results come back within normal RF ranges, but their symptoms persist, doctors may use other tests to help identify the underlying cause. They may also repeat lab studies going forward.
The RA latex turbid test alone cannot give a clear enough picture to make a diagnosis, so doctors will usually use other tests in the initial evaluation. They may also order imaging studies, including X-rays of hands and feet, before making a diagnosis.
If a person's results show only a slightly higher value than normal, doctors will probably order additional tests.
Most people who undergo an RA latex turbid test can also expect to have an anti-cyclic citrullinated antibody (anti-CCP) test, which is a blood test that checks for the levels of anti-CCP.
Anti-CCP is an antibody that is more specific for RA. According to some research, it is present in about 60–70% of people with RA.
Other tests include:
- C-reactive protein (CRP) tests: CRP tests measure a reactive protein that the liver creates. Higher levels of CRP indicate inflammation.
- Complete blood count (CBC): A CBC test looks at both red and white blood cell counts, which may help identify anemia, infection, and any secondary effects of the underlying condition.
- Antinuclear antibody (ANA) panel: An ANA panel tests for the presence of autoantibodies directed at particles inside cells, which are a sign of autoimmune conditions.
- Erythrocyte sedimentation rate (ESR): The ESR test measures how fast red blood cells settle to the bottom of a container. Cells that fall faster indicate inflammation, as well as high levels of proteins in the blood.
- Joint aspiration: For this test, doctors pull fluid from the joints to analyze it for white blood cells, crystals, or infectious organisms.
- Ultrasounds or X-rays: Imaging tests can help identify inflammation or show signs of wear and tear or damage (erosions) in the joints.
What else causes high results?
A doctor may recommend other tests to accurately diagnose RA.
While doctors typically order RA latex turbid tests to check for RA, other issues can cause abnormal results.
Other conditions that may cause a person to have high RF values include:
- some cancers, such as leukemia or multiple myeloma
- viral infections, such as HIV, mononucleosis, or hepatitis C
- Sjogren's syndrome
Rarely, otherwise healthy adults may have higher RA latex turbid values without having an underlying medical condition.
An RA latex turbid test can help doctors identify high RF levels in the blood. High RF levels can indicate RA.
However, tests that help identify RF levels may not provide enough information to make a diagnosis, so a doctor will usually recommend additional tests.