Introduction

Rheumatoid arthritis (RA) is a chronic autoimmune disease that affects millions of people worldwide. Early and accurate diagnosis of RA is crucial for initiating timely treatment and improving patient outcomes. In recent years, testing and monitoring the rheumatoid factor (RF) biomarker have emerged as powerful tools in RA diagnosis and investigation. 

Testing and monitoring RF levels play a pivotal role in the diagnosis and management of RA. Here are key reasons why it's important to utilise RF testing:

1. Early Diagnosis: Detecting RA in its early stages is vital to prevent irreversible joint damage. RF testing helps identify the presence of RA, even before clinical symptoms fully manifest, enabling healthcare professionals to initiate early interventions.
2. Confirming Diagnosis: RF is strongly associated with RA. Positive RF test results provide valuable confirmation of the diagnosis, especially when combined with other clinical assessments, such as patient history, physical examination, and imaging studies.
3. Prognostic Indicator: RF levels can serve as a prognostic indicator for disease severity and progression. Higher RF levels are often associated with more aggressive disease manifestations, increased joint damage, and a higher likelihood of developing complications.
4. Treatment Decisions: RF testing aids in tailoring treatment plans. High RF levels may indicate a need for more aggressive treatment strategies, such as disease-modifying antirheumatic drugs (DMARDs), to effectively manage RA and minimise joint damage.
5. Monitoring Disease Activity: Regular monitoring of RF levels allows healthcare professionals to assess disease activity and treatment response. Serial RF testing helps evaluate the effectiveness of therapeutic interventions and adjust treatment plans accordingly.

Reference Ranges and Values Interpretation

The discovery of rheumatoid factor (RF) marked the identification of the first autoantibody found in individuals with rheumatoid arthritis (RA). Autoantibodies, which develop in response to the body's own tissues, are characteristic of autoimmune diseases like RA. However, despite its name, RF is not exclusive to RA, and there are various factors that can influence RF lab results. It is worth noting that around 20% of individuals with confirmed RA may not exhibit abnormal RF test results, while approximately 5% of people without RA may show abnormal RF test results. Thus, negative RF levels do not rule out the presence of the disease, and positive levels do not guarantee an RA diagnosis.

The normal range of RF is typically defined as 0-30 IU/ml. RF levels exceeding 20 IU/ml alone are not sufficient for diagnosing RA, as there are other factors that can contribute to an elevated RF level. Several conditions and medical procedures can result in increased RF levels, including other autoimmune diseases, certain chronic infections, diabetes, bacterial endocarditis, cancer, normal aging, vaccinations, and transfusions. It is important to note that even if the disease goes into remission, an elevated RF level often persists once it has been detected.

Interpreting RF test results involves understanding reference ranges and values associated with the test. Here's a breakdown of RF values interpretation.

1. Negative: RF levels below the upper limit of the reference range indicate a negative result. While this suggests a lower likelihood of RA, it does not rule out the disease entirely, as some individuals with RA may have seronegative results.

2. Low Positive: RF levels slightly above the upper limit of the reference range may be considered a low positive result. Further investigation, including additional diagnostic tests, is typically recommended to confirm the presence of RA.

3. Moderate Positive: RF levels significantly exceeding the upper limit of the reference range strongly suggest RA. Combined with clinical evaluation, a moderate positive result aids in establishing a confident diagnosis.

4. High Positive: RF levels well above the upper limit of the reference range are highly indicative of RA. Such results are often associated with more severe disease manifestations, increased joint damage, and a need for aggressive treatment.

You can track your RF biomarker in the Health Dashboard.

Limitations of RF Testing

While RF testing is a valuable tool, it does have limitations that need to be considered:

1. False Negatives: Some individuals with RA may have negative RF results, particularly in the early stages of the disease. These cases are known as seronegative RA. In such instances, additional diagnostic tests, such as anti-cyclic citrullinated peptide (anti-CCP) antibodies, may be necessary to confirm the diagnosis.
2. False Positives: RF can also be found in the blood of individuals without RA or other autoimmune diseases. Elevated RF levels may be present in other conditions, including chronic infections, certain malignancies, and other autoimmune disorders. Therefore, clinical correlation and evaluation of additional diagnostic markers are crucial to avoid false-positive results.
3. Variability in RF Levels: RF levels can fluctuate over time, even in individuals with established RA. Monitoring trends in RF levels and considering changes in clinical presentation are essential for accurate disease assessment and treatment decisions.

Difference between Capillary and Venous Samples

When obtaining blood samples for RF testing, you have a choice between capillary and venous samples. Here's an overview of their differences:

1. Capillary Samples: Capillary blood samples are obtained through a finger prick. They offer advantages such as ease of collection, reduced discomfort and faster results. Capillary sampling is particularly useful in home kits format or situations where venous access in a clinic is challenging. However, it's important to establish separate reference ranges for capillary samples to ensure accurate interpretation, as RF levels in capillary blood may slightly differ from those in venous blood. Make sure that the laboratory you use is calibrated for capillary samples and EQA verified. We use Sussex Pathology Diagnostics Laboratory that specialises in capillary sample processing.
2. Venous Samples: Venous blood samples are drawn from a vein, typically in the arm, and are the standard method used in most clinical settings, such as our walk-in clinics. Venous sampling provides larger blood volumes and is well-suited for comprehensive laboratory analysis. It is recommended when detailed investigations and additional diagnostic tests are required.

Testing and monitoring the rheumatoid factor biomarker have revolutionised the diagnosis and investigation of rheumatoid arthritis. RF testing plays a crucial role in early diagnosis, confirmation of RA, prognostication, treatment decision-making, and monitoring disease activity.

However, it is essential to consider the limitations of RF testing and interpret results in conjunction with clinical findings. By embracing RF testing and leveraging its benefits, you can enhance RA management and improve outcomes.