The Rheumatoid Factor (RF) test is a blood test that measures the level of RF antibodies in the blood. RF antibodies are produced by the immune system and may attack healthy tissues in the body by mistake, leading to autoimmune disorders like rheumatoid arthritis. In this article, we will cover an in-depth overview of the RF test.

What is the Rheumatoid Factor (RF) Test?

The Rheumatoid Factor or RF test is a blood test that detects the presence and level of rheumatoid factor antibodies in the blood. 

• High levels of RF in the blood can indicate rheumatoid arthritis or other autoimmune disorders. 
• Some people with normal RF levels may still have rheumatoid arthritis. 
• Some healthy individuals can have slightly elevated RF levels.

Purpose of the Rheumatoid Factor Test

The main purpose of the RF test is to aid in the diagnosis of rheumatoid arthritis, especially in conjunction with other blood tests and clinical signs and symptoms. It may also be used to:

• Monitor disease progression and treatment effectiveness in people already diagnosed with rheumatoid arthritis.
• Help diagnose other autoimmune disorders like Sjögren's syndrome and systemic lupus erythematosus.
• Understand how severe rheumatoid arthritis may be and if it's likely to affect organs outside joints.

When is a Rheumatoid Factor Test Needed?

A doctor may recommend a RF test if someone has symptoms that could indicate rheumatoid arthritis, such as:

• Joint pain, swelling, stiffness, tenderness or warmth, especially affecting both sides of the body equally
• Prolonged morning joint stiffness lasting over 30 minutes
• Low-grade fever
• Fatigue
• Reduced appetite and weight loss
• Firm lumps under the skin
• Dry eyes/mouth
• Anaemia

People at high risk of developing the disease, like those with a family history of rheumatoid arthritis, may also need to get tested even without symptoms.

What Happens During the RF Test?

The RF test is performed by drawing a small sample of blood, usually from the patient’s arm, in a simple procedure that takes less than 5 minutes. The steps below outline what patients can expect during sample collection:

Pre-Procedure

• You may need to show a few documents like a lab requisition or doctor's order for the test at the collection centre.
• If undergoing any blood-thinning therapies, it is advisable to check whether they need to be stopped before the blood test to prevent risks of excess bleeding complications.

During Blood DraW

• A tourniquet is tied a few inches above the elbow crease to slow blood flow and plump the veins.
• The blood draw site at the antecubital fossa or forearm near the bend of the elbow is cleaned with an alcohol wipe. This prevents infection risk.
• A needle attached to a sample collection tube is inserted into the vein. A few small tubes of blood are then drawn into the vacuum tube. 

Post-Procedure Care

• Drink plenty of water and have a light snack to counter any light-headedness. If bleeding restarts, reapply pressure firmly. 
• Avoid strenuous physical activity, heavy lifting or repetitive movements with the arm for the rest of the day to minimise discomfort or bleeding risks.
• Watch for signs of infection, bleeding, sustained pain or lack of healing at the site over the next day.

Uses of the Rheumatoid Factor Test

The RF test can help health professionals:

• Diagnose rheumatoid arthritis, especially when combined with symptoms and other blood test findings like elevated ESR and CRP.
• Understand the severity and predict outcomes of rheumatoid arthritis since higher RF levels correlate with higher disease activity and more aggressive joint damage.
• Monitor the effectiveness of rheumatoid arthritis treatments over time. Falling RF levels indicate the treatment is working well to control disease activity and joint injury pathways.   
• Distinguish rheumatoid arthritis from osteoarthritis since the latter does not involve antibodies like RF. 
• Diagnose other RF-associated autoimmune disorders. 
• Evaluate bone and joint infection risks in procedures. 

How Painful is the RF Test?

The RF test involves a brief needle prick that may cause slight pain or discomfort. There may be mild bruising or soreness around the puncture site afterwards, but this typically resolves within a day. 

Using a topical anaesthetic prior to drawing blood can minimise discomfort. 

How to Prepare for the RF Test 

No special preparations are required for RF testing. Patients should:

• Continue taking medications as scheduled unless explicitly asked to hold certain drugs like blood thinners  
• Stay well hydrated 
• Have a light meal before sample collection
• Wear short sleeves or loose clothing for easy access to arm veins  
• Avoid caffeine for a few hours prior if prone to anxiety during blood draws

What do RF Test Results Mean?

RF test results are interpreted as either positive/abnormal (higher RF level) or negative/normal (little to no RF detected):

Negative results: 

• This indicates normal or undetectable RF levels, generally below 20 IU/mL, depending on the lab reference used. 
• However, it does not rule out rheumatoid arthritis since many (15-30%) rheumatoid arthritis patients have negative RF tests. 
• Other blood markers (e.g. anti-CCP) or imaging would be used to aid diagnosis if clinical suspicion is still high.

Low Positive results: 

• This signals minimally elevated RF levels between 20-60 IU/mL. 
• May require further evaluation based on symptom review. 
• Retesting may be done since this zone could represent natural fluctuations. 

High Positive results: 

• Having RF levels > 60 IU/mL raises the likelihood of an RF-mediated disorder like rheumatoid arthritis. 
• Over 90 IU/mL has high specificity for rheumatoid arthritis. 
• However, clinical correlation is still necessary for diagnosis confirmation since other conditions can also cause very high RF levels. 

Conclusion  

The rheumatoid factor or RF test is an important blood test that aids in the diagnosis and monitoring of rheumatoid arthritis. By detecting RF antibodies that can attack healthy tissues, it provides insight into immune dysfunction linked to rheumatoid arthritis. However, both false positive and false negative results are possible, demonstrating the need to interpret RF test results in conjunction with clinical findings and not in isolation. Talk to your healthcare provider if you have any concerns about your rheumatoid factor test result.

FAQs

1. What is a normal rheumatoid factor level? 

Ans: A normal RF level is typically less than 20-40 IU/mL. However, laboratories can set slightly different ranges for normal. Always interpret your result based on the reference range your laboratory provides.  

2. What happens if the rheumatoid factor test is positive?

Ans: A positive RF test indicates elevated rheumatoid factor levels in the bloodstream. This may signify if rheumatoid arthritis or another RF-associated condition is present. However, further evaluation of symptoms and additional testing would be needed to confirm a diagnosis. 

3. What happens if the rheumatoid factor test is negative?

Ans: A negative RF test means rheumatoid factor levels were within the normal range or undetectable. However, rheumatoid arthritis cannot be ruled out even with a negative RF test - around 15-30% of rheumatoid arthritis patients have negative RF tests. Other blood markers or clinical criteria would be used to aid diagnosis.

4. What are some possible complications of the rheumatoid factor test?

Ans: The RF test is a routine blood draw that rarely has complications when performed correctly. Possible but unlikely complications include excess bleeding from the puncture site, lightheadedness or fainting, infection at the puncture site and hematoma or nerve injury from poorly placed needles.

5. How long does the rheumatoid factor test take to perform?

Ans: Having blood drawn for the RF test takes less than 5 minutes. Waiting for test results can take anywhere from a few hours to 1-2 days depending on the testing laboratory. Results are typically available within 24 hours.