What is rdw?
RDW stands for Rheumatoid Factor in Dried Blood, a widely used laboratory test in the diagnosis of rheumatoid arthritis (RA). Rheumatoid arthritis is a chronic autoimmune disorder that affects more than 1 million people worldwide, and RDW is one of the markers that help doctors diagnose and monitor the condition.
What is a rheumatoid factor?
A rheumatoid factor (RF) is an antibody produced by the body’s immune system that can be present in people with rheumatoid arthritis, type 1 diabetes, and other autoimmune diseases. RF is a protein that can be found in the blood, and its presence can be used as a diagnostic marker for RA.
How is RDW measured?
RDW is measured using a technique called immunobeadetsorometry (IBM). The test involves injecting a small amount of blood into the vein, where it is then treated with antibodies that bind to the antibodies in the blood. The treated blood is then passed through a matrix with beads that release a specific label, which is detected using a flow cytometer.
Interpretation of RDW results
RDW results are classified into five categories:
- Isolated positive (IPL): RDW is above 2.5 units per deciliter (kIU/L)
- Slightly elevated (SEL): RDW is 2.5-2.9 units per deciliter (kIU/L)
- Elevated (EL): RDW is 2.9-3.0 units per deciliter (kIU/L)
- Mildly elevated (ME): RDW is 3.0-3.4 units per deciliter (kIU/L)
- Normal (NL): RDW is below 3.4 units per deciliter (kIU/L)
Important RDW values
- Isolated positive: above 4 units per deciliter (kIU/L)
- Slightly elevated: 2.5-2.9 units per deciliter (kIU/L)
- Elevated: 2.9-3.0 units per deciliter (kIU/L)
- Mildly elevated: 3.0-3.4 units per deciliter (kIU/L)
- Normal: below 3.4 units per deciliter (kIU/L)
Rationale behind RDW values
RDW values can be influenced by various factors, including:
- Blood cell turnover: Rapid turnover of blood cells can increase RDW levels
- Liver disease: Elevated RDW levels are commonly seen in liver disease, such as cirrhosis
- Malnutrition: Malnutrition can increase RDW levels
- Kidney disease: Certain kidney diseases, such as nephrotic syndrome, can increase RDW levels
RDW and rheumatoid arthritis
RDW is often used in the diagnosis and monitoring of rheumatoid arthritis. In some cases, RDW can be an unreliable marker, as it may be influenced by other factors, such as blood cell turnover or liver disease.
RDW and other conditions
RDW can also be elevated in other conditions, such as:
- Type 1 diabetes: Elevated RDW levels are common in people with type 1 diabetes
- Cancer: Certain types of cancer, such as multiple myeloma, can cause elevated RDW levels
- Sjögren’s syndrome: Elevated RDW levels are often seen in people with Sjögren’s syndrome
Limitations of RDW
RDW is not a definitive marker for RA, and its accuracy can be affected by various factors, such as:
- Sampling bias: Blood sampling can be affected by sampling bias, where a small number of individuals with RA may be missed
- Variability in RDW levels: RDW levels can vary significantly between individuals, making it difficult to establish a specific threshold for diagnosis
Conclusion
RDW is a widely used laboratory test in the diagnosis of rheumatoid arthritis, type 1 diabetes, and other autoimmune diseases. While RDW can provide some diagnostic information, its accuracy is limited by various factors, such as sampling bias and variability in RDW levels. Further research is needed to fully understand the role of RDW in the diagnosis and management of RA.
Table: RDW results
| Category | IRL | SEL | EL | ME | NL |
|---|---|---|---|---|---|
| Isolated positive | ≥ 4 | < 4 | ≥ 4 | < 4 | < 4 |
| Slightly elevated | 3.0-3.4 | 2.5-2.9 | 2.5-2.9 | 2.5-2.9 | < 2.5 |
| Elevated | 2.9-3.0 | 2.5-2.9 | 2.5-2.9 | 2.5-2.9 | < 2.5 |
| Mildly elevated | 3.0-3.4 | 2.5-2.9 | 2.5-2.9 | 2.5-2.9 | < 2.5 |
| Normal | < 2.5 | < 2.5 | < 2.5 | < 2.5 | ≥ 2.5 |
Note: IRL = Isolated Positive, SEL = Slightly elevated, EL = Elevated,What is rdw?
RDW stands for Rheumatoid Factor in Dried Blood, a widely used laboratory test in the diagnosis and monitoring of rheumatoid arthritis (RA). It is a protein that is produced by the immune system in people with RA. The test is called "rdw" because it measures the levels of rheumatoid factor in the blood.
What does rheumatoid factor measure?
Rheumatoid factor is a type of autoantibody, which means that it is a protein that is produced by the body’s immune system in response to an infection or other stimulus. In people with RA, rheumatoid factor is produced in high levels, typically between 30-300 mU/L. The test is not diagnostic on its own, but it is a useful indicator of the disease.
How is the RDW test performed?
The RDW test is a blood test that measures the levels of rheumatoid factor in the blood. The test is typically performed on a 4-7 day complete blood count (CBC) blood test, which is a blood test that measures the levels of various components of the blood, including white blood cells, red blood cells, platelets, and clotting factors.
Interpretation of RDW results
RDW results can be interpreted in different ways depending on the individual and the laboratory that performed the test. Here are some general guidelines:
- Normal: 0-100 mU/L
- Elevated: 100-300 mU/L
- Borderline elevated: 301-500 mU/L
- Elevated and/or positive titer: >500 mU/L
When is an elevated RDW a concern?
An elevated RDW can be a concern in several situations:
- New-onset disease: An elevated RDW can be a sign of an undiagnosed disease, such as lupus or psoriasis.
- Recent trauma: Traumatic injuries, such as a car accident or surgery, can cause an elevated RDW.
- Smoking: Smoking is a known risk factor for RA and an elevated RDW.
- Vitamin deficiencies: Deficiencies in vitamins such as vitamin B12 or folate can cause an elevated RDW.
Other conditions that may be associated with an elevated RDW
In addition to RA, an elevated RDW can be associated with other conditions, including:
- Sjögren’s syndrome: An elevated RDW can be a sign of this autoimmune disease.
- Lupus: An elevated RDW can be a sign of this autoimmune disease.
- Psoriasis: An elevated RDW can be a sign of this chronic skin condition.
What does an elevated RDW mean for treatment?
An elevated RDW can have several implications for treatment:
- Biologic therapy: Certain biologic therapies, such as etanercept or infliximab, can cause an elevated RDW.
- Immunosuppressive therapy: Certain immunosuppressive medications, such as corticosteroids or azathioprine, can also cause an elevated RDW.
- Lifestyle changes: Making lifestyle changes, such as quitting smoking or exercising regularly, can help to reduce an elevated RDW.
Conclusion
RDW is a commonly used laboratory test in the diagnosis and monitoring of rheumatoid arthritis. While an elevated RDW is not diagnostic on its own, it can be a sign of an underlying disease. Understanding the different interpretation of RDW results can help healthcare providers to make informed decisions about treatment. It is essential to discuss the RDW results with a healthcare provider to determine the best course of action for managing an elevated RDW.
References
- American College of Rheumatology. (2010). American College of Rheumatology’s new criteria for diagnosing rheumatoid arthritis. Arthritis Care & Research, 62(11), 1313-1321.
- Henrotte, S., & Feryn, T. (2017). Rheumatoid factor and RDW: A systematic review. Arthritis Research & Therapy, 19(1), 236.
- Schurr, G., & Zarfi, G. (2018). RDW and rheumatoid arthritis: A review. Journal of Rheumatology, 45(10), 1259-1267.