If you've recently had a blood test, you may have seen "RDW" on your results and wondered what it means. Red Cell Distribution Width (RDW) measures how much the size of your red blood cells varies, which can help detect conditions like anemia or nutritional deficiencies. This article discusses why RDW matters, how it’s measured, and what it can reveal about your health.
[signup]
What Does the RDW Blood Test Measure?
RDW, or Red Cell Distribution Width, indicates how much the size of red blood cells varies in a blood sample. While healthy red blood cells are generally uniform in size, significant size variation (anisocytosis) can suggest certain medical conditions. A higher RDW means more cell size variation, which is often linked to conditions like anemia or nutrient deficiencies (e.g., iron, vitamin B12, or folate).
Correlation with Other CBC Parameters
RDW is part of the Complete Blood Count (CBC), which provides a full overview of your blood.
It is often interpreted alongside other CBC components, such as Mean Corpuscular Volume (MCV). MCV measures the average size of red blood cells, while RDW shows how much they differ from that average. These two measurements help doctors better understand blood health and identify potential causes of anemia or other blood-related conditions.
Why Is the RDW Blood Test Important?
Red blood cells carry oxygen throughout the body, making their size and function essential for overall health. The RDW blood test helps doctors evaluate red blood cell health and identify potential health issues.
Diagnostic Value
RDW is particularly useful in diagnosing anemia, as it helps doctors differentiate between various types. For example, a high RDW can indicate iron deficiency anemia, where red blood cells vary greatly in size due to a lack of iron. Similarly, RDW is also used to detect deficiencies in vitamin B12 or folate, which can lead to larger than normal red blood cells. When RDW is elevated along with other indicators, it can provide key clues to the specific cause of anemia.
RDW can also help diagnose chronic conditions. High RDW levels are linked to cardiovascular diseases like heart failure and atherosclerosis, where poor circulation affects red blood cell production. Increased RDW can also indicate liver disease, as liver dysfunction impacts red blood cell size. Inflammatory disorders, such as rheumatoid arthritis, can also raise RDW levels due to chronic inflammation.
Understanding RDW Blood Test Results
The typical reference range for RDW in adults is 11.5% to 15%, though this can vary slightly between labs. Values outside this range may signal an underlying health issue.
High RDW Results
Elevated RDW levels often indicate variations in red blood cell size, which can be linked to several conditions. High RDW is commonly associated with macrocytic anemia, where red blood cells are larger than normal, often due to vitamin B12 or folate deficiency. It can also suggest iron deficiency anemia, where red blood cells vary in size due to a lack of iron. Other possible causes of high RDW include liver disease or chronic inflammation.
Low RDW Results
A low RDW result means red blood cells are similar in size and close together. This isn't a sign of anemia and is not a cause for concern.
Clinical Applications of RDW Blood Test
RDW may have certain clinical applications:
RDW in Cardiovascular Health
RDW may be an important marker for predicting heart diseases like heart failure and atherosclerosis. It reflects changes in red blood cell production and quality, which can be influenced by poor circulation or inflammation.
One study consisting of 25,612 participants found that an abnormal RDW is linked to an increased risk of first-time myocardial infarction (MI). For every 1% increase in RDW, the risk of MI rose by 13%. This connection remained even after excluding participants with anemia. The study concluded that RDW is directly linked to MI risk, regardless of anemia or other cardiovascular factors.
A review of the literature further links RDW to heart failure outcomes. Initially used to diagnose anemia, RDW is now associated with both acute and chronic heart failure. Elevated RDW may result from inflammation, oxidative stress, and poor nutrition, though the exact cause remains unclear. RDW is now used to assess the risk of heart failure. More research is needed to determine if RDW could be targeted in treatment.
Another study found that higher RDW levels in heart disease patients who underwent percutaneous coronary intervention (PCI) or stent procedures were linked to a greater risk of serious heart problems. PCI, or stent procedure, is a treatment to open blocked arteries and improve blood flow. The study also showed that older patients and those with high cholesterol faced an even higher risk when RDW levels were elevated.
RDW in Chronic Disease Monitoring
RDW is also used to monitor chronic diseases over time. For patients with conditions like chronic kidney disease, liver disease, or inflammatory disorders, RDW levels can help assess how the disease affects red blood cell production. Tracking changes in RDW over time allows healthcare providers to understand disease progression better, adjust treatments, and identify potential complications early.
How is the RDW Blood Test Performed?
The RDW test is part of a standard blood workup to assess red blood cell health.
Testing Procedure
The RDW test is included in a Complete Blood Count (CBC), a routine blood test that examines different blood components, including red blood cells, white blood cells, and platelets.
During venipuncture, a blood sample is taken from a vein in your arm. The procedure is quick and minimally invasive. The blood sample is then sent to a lab for analysis to measure the RDW. Results are usually available within a few hours. RDW and other CBC markers help doctors identify conditions such as anemia and chronic diseases.
Preparation and Precautions
No special preparation is required for the RDW test, though you may need to follow specific instructions if other tests (like fasting blood work) are being done. Discussing your results with your doctor is important, as RDW values must be interpreted alongside other markers and in the context of your overall health.
Limitations of the RDW Blood Test
While the RDW test offers valuable insights, it has limitations when diagnosing specific conditions.
What RDW Can and Cannot Tell You
RDW measures red blood cell size variation but doesn’t identify the exact cause. For instance, a high RDW may indicate anemia but doesn’t specify whether it’s due to iron or vitamin B12 deficiency. RDW can suggest underlying issues but requires further testing for a definitive diagnosis.
Need for Complementary Tests
Since RDW alone can’t confirm a diagnosis, healthcare providers often order additional tests. If RDW is elevated, tests for iron levels, vitamin B12, or other markers may be needed. Additional procedures help provide a complete picture of a patient’s health, making RDW just one part of the diagnostic process.
Frequently Asked Questions (FAQs)
What does a high RDW mean?
A high RDW indicates that the body is not producing red blood cells of the same size. This elevation in RDW suggests conditions like anemia, nutritional deficiencies (like iron, B12, or folate), or chronic diseases. However, high RDW doesn’t identify a specific cause, so further tests are needed to determine the underlying issue.
How can I lower my RDW levels?
There’s no direct way to lower RDW levels without addressing the root cause. If elevated RDW is due to anemia or a nutrient deficiency, treating the deficiency can help normalize red blood cell production. For chronic conditions contributing to high RDW, managing the condition may help bring levels back to normal.
For individuals with chronic diseases contributing to high RDW, managing the condition with appropriate treatment can also help bring RDW levels back into the normal range. Always consult with a healthcare provider to determine the best treatment options.
What are normal RDW levels?
Optimal RDW levels in adults typically range from 11.5% to 15%, though this can vary slightly by lab. Values outside this range may indicate an underlying condition. However, they should be considered alongside other test results for a complete assessment. Your doctor can explain what your specific RDW levels mean in the context of your health.
[signup]
Key Takeaways
- RDW helps assess red blood cell health and can indicate conditions like anemia, nutrient deficiencies, and chronic diseases.
- RDW results don't provide a complete diagnosis and must be interpreted alongside other blood test results.
- Further testing and monitoring may be needed to identify the root cause of health concerns.
- Consult a healthcare provider to understand your RDW results and determine the best treatment approach.
%201.svg){kind=logo}
Ready to become a world class gut health expert? Join Jeannie Gorman, MS, CCN, for a 
