RDW-CV Testing 101: Top Tests And Understanding Results

In 1674 Antoni van Leeuwenhoek first visualized red blood cells, saying they were “25,000 times smaller than a grain of sand,” so it is amazing how much they affect our health!

Healthy red blood cells carry oxygen to essentially every cell in your body, giving you the energy to function and thrive. Problems with red blood cells can quickly leave you feeling unwell: that’s why they are commonly assessed in routine blood work.

One important tool used to assess red blood cell health is the Red Cell Distribution Width-Coefficient of Variation (RDW-CV). This test measures the variability in the size of red blood cells (RBCs), and it can offer insights into a variety of health conditions including anemia, nutrient deficiencies, and chronic diseases.

In this article, we’ll explore what RDW-CV is, why it’s important, when to consider testing, and how to interpret the results—both for patients and practitioners.

Additionally, we’ll highlight complementary functional medicine tests that can provide a more complete picture of your health when RDW-CV levels are abnormal.

[signup]

What is RDW-CV?

The Red Cell Distribution Width-Coefficient of Variation (RDW-CV) is a key metric used in blood tests to assess the variation in the size of red blood cells. Healthy RBCs are generally uniform in size, which helps them efficiently carry oxygen from the lungs to tissues throughout the body.

RDW-CV measures how much variation exists between the sizes of red blood cells in a sample and is typically reported as a percentage.

A higher RDW-CV indicates that there is more variability in RBC size, while a lower RDW-CV shows that the RBCs are more uniform.

What’s the Difference Between the RDW-CV and the RDW-SD?

RDW-CV and RDW-SD (Standard Deviation) are both ways of measuring RBC size variation. While RDW-CV expresses the variation between red blood cell sizes as a percentage, RDW-SD measures the actual distribution of RBC sizes in femtoliters.

Both provide useful information, but RDW-CV is more commonly used in routine blood work.

When to Order RDW-CV Testing

RDW-CV is typically ordered as part of a Complete Blood Count (CBC), a standard test often included in routine medical evaluations.

A healthcare provider might order a CBC and check RDW-CV if a patient presents symptoms like fatigue, weakness, shortness of breath, or pale skin—common indicators of anemia and other blood disorders.

Conditions commonly associated with elevated RDW-CV levels include:

Iron Deficiency Anemia: insufficient iron can cause the production of smaller, varied-sized RBCs, leading to an elevated RDW.

Vitamin B12 or Folate Deficiency: both deficiencies can lead to the production of abnormally large RBCs, increasing size variability.

Hemolytic Anemia: RBC destruction and production of new RBCs of various sizes raise RDW levels.

Chronic Diseases: conditions like kidney disease, liver disease, or inflammatory disorders can disrupt RBC production, increasing RDW.

Bone Marrow Disorders: diseases like myelodysplastic syndrome (MDS) can affect RBC production, leading to abnormal cell sizes and shapes.

Low RDW-CV, on the other hand, typically indicates uniform RBC size and is generally not a cause for concern.

RDW-CV as Part of a Complete Blood Count (CBC)

The RDW-CV test is usually performed as part of a Complete Blood Count (CBC), which provides a detailed look at your blood's components.

A CBC is now considered routine blood work, and it is a first-line lab test run for any symptoms that may involve red or white blood cells.

It can be used to assess symptoms such as unexplained fever, weakness, lethargy, bruising, and others; to monitor chronic conditions such as chronic kidney or liver disease; and to monitor overall health.

RDW-CV, often part of the CBC, is a key measurement when assessing red blood cell health, particularly in diagnosing different types of anemia. It is especially useful when paired with the Mean Corpuscular Volume (MCV), a measurement of the average size of RBCs.

For example, a high RDW-CV with a low MCV may indicate iron deficiency anemia, while a high RDW-CV with a high MCV could point to vitamin B12 or folate deficiency. This combination allows healthcare providers to get a clearer picture of what's happening in the blood and to tailor treatment accordingly.

What’s the Difference Between RDW and MCV?

RDW measures the variation in red blood cell size, while MCV indicates the average size of red blood cells. Together, they help diagnose and classify types of anemia by assessing both the range of cell sizes (RDW) and the average cell size (MCV).

Top Functional Medicine Tests to Consider When RDW-CV is Abnormal

When RDW-CV results are abnormal, additional testing can help identify the root causes of RBC size variability and guide treatment.

Functional medicine offers a holistic approach to interpreting RDW-CV via complementary tests to provide a more comprehensive understanding of health.

Here are the top functional medicine tests to consider if RDW-CV is abnormal:

Micronutrient Testing

This comprehensive test assesses levels of vitamins and minerals needed for RBC production such as iron, vitamin B12, and folate. Micronutrient deficiencies are common causes of high RDW-CV, and testing can help identify which nutrients are lacking.

Comprehensive Metabolic Panel (CMP)

A CMP evaluates liver and kidney function, as chronic diseases affecting these organs can disrupt RBC production and lead to elevated RDW-CV levels. Functional medicine practitioners often use CMP results to understand the broader metabolic context of blood cell health.

Inflammatory Markers

Tests like C-reactive protein (CRP) or homocysteine can be helpful for assessing chronic inflammation, which is often linked to elevated RDW-CV levels. Chronic inflammation can affect RBC production and lifespan, making these markers important to consider.

Bone Marrow Biopsy

In more severe cases where a bone marrow disorder like myelodysplastic syndrome is suspected, a biopsy may be required. This test evaluates the production of blood cells at the source and can help diagnose disorders affecting bone marrow function.

This determination is made by a medical specialist such as a hematologist or oncologist; in the case of unclear laboratory assessments or troubling symptoms, a prompt referral should be made.

Understanding RDW-CV Results

Interpreting RDW-CV results requires a look at the bigger picture. RDW-CV alone provides valuable information, but it’s most informative when evaluated alongside other tests such as MCV or specific nutrient levels.

High RDW-CV

As discussed, a high RDW-CV indicate a condition known as anisocytosis, which means there is a greater variability in the size of red blood cells. Anisocytosis often indicates anemia or a related condition. For example:

Iron Deficiency Anemia: in this type of anemia, the body produces smaller, irregularly shaped RBCs, raising RDW-CV.

Vitamin B12 or Folate Deficiency: these deficiencies lead to the production of larger RBCs, increasing variability.

Chronic Conditions: elevated RDW-CV is also associated with conditions like chronic kidney disease, liver disease, and inflammatory disorders. The cause of the anisocytosis in this setting relies on many factors including increased inflammation, possible nutrient deficiencies, impaired red blood cell production, and other possible causes.

Low RDW

Low RDW-CV means that most RBCs are of similar size, which is generally considered normal and not concerning. Low RDW-CV alone is not typically indicative of any health issues.

RDW-CV and Chronic Disease Risk

Recent research has shown that RDW-CV is more than just a marker for anemia—it can also serve as a predictor for chronic disease risk, particularly in cardiovascular disease (CVD) and metabolic conditions like diabetes.

Cardiovascular Disease (CVD)

It’s well accepted that elevated RDW-CV can be an early marker for cardiovascular disease and overall mortality risk. This may be due to the role of inflammation and oxidative stress in both red blood cell production and cardiovascular health.

RDW-CV may be considered part of a broader assessment of cardiovascular risk factors.

Diabetes and Metabolic Syndrome

High RDW-CV is often associated with heart failure and diabetes mellitus, reflecting increased inflammation (which often correlates with diabetes) and poor metabolic health.

This elevation in RDW may be linked to the effects of high glucose levels on red blood cell structure and function, as well as the higher inflammatory burden and potential nutrient deficiencies seen in diabetic patients.

Chronic Inflammatory Diseases

Conditions such as chronic kidney or liver disease and systemic inflammatory disorders, can cause elevated RDW-CV by disrupting the normal production and turnover of red blood cells. Monitoring RDW-CV in these patients can provide insights into the progression of their disease and the effectiveness of treatments.

Integrating RDW-CV Testing into a Functional Medicine Approach

Functional medicine takes a holistic view of health, recognizing the interconnection between various systems in the body. RDW-CV, when used alongside other tests, can provide important clues about overall health, oxidative stress, and nutrient status.

Functional medicine practitioners often use RDW-CV as a starting point for a more in-depth investigation into a patient’s overall well-being.

Correcting abnormal RDW-CV involves treating the underlying cause, whether it’s iron deficiency, vitamin B12 deficiency, or a chronic condition. This may involve:

Nutritional interventions: improving the intake of key nutrients like iron, B12, and folate can help normalize RDW-CV.

Supplementation: targeted supplementation of deficient vitamins and minerals may be recommended to support RBC health.

Addressing chronic conditions: treating the underlying causes of chronic diseases like kidney disease or inflammation is key to improving RDW-CV levels and overall health.

Next Steps After RDW-CV Testing

After receiving RDW-CV results, it’s important to follow up with your healthcare provider to discuss the findings and any additional tests that may be needed. If the RDW-CV is elevated, follow-up tests like nutrient testing or a comprehensive metabolic panel can provide more specific information about the root causes.

Patients should also consider re-testing their RDW-CV levels periodically, especially after starting treatments or making significant lifestyle changes to address nutrient deficiencies or chronic conditions.