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What is RDW (Red Cell Distribution Width) in a Blood Test?

Doctors often suggest patients take a Red Cell Distribution Width test or RDW test to identify the size and volume of their red blood cells (RBCs) or erythrocytes. RBCs are essential for carrying oxygen from the lungs to other body parts. Hence, doctors might need to know about the current status of erythrocytes in your body to treat you better.

Do you wish to find out more about RDW in a blood test? Then, keep reading this article to get a complete guide.

Table of Contents

What is an RDW Test?

Why is it Necessary?

When to Get an RDW Test?

Procedure for the RDW Test

Preparation for RDW Test

How is RDW Measured?

How to Read Results?

Normal Range of RDW Test

Symptoms of High RDW

What If RDW is High?

Causes of High RDW

Symptoms of Low RDW

What If RDW is Low?

Causes of Low RDW

Frequently Asked Questions

What Is RDW in a Blood Test?

The human body comprises numerous red blood cells of various shapes and sizes. Generally, these are disk-shaped, with a 6.2 to 8.2 micrometres diameter. A haemoglobin protein binds these cells with oxygen, carrying it across various tissues. If you face issues with your haemoglobin, they can negatively influence the flow of oxygen and the size, shape, and health of red blood cells. This can cause multiple health issues.

Thus, the meaning of RDW in a blood test is associated with identifying the details of the volume and size of red blood cells. It helps doctors analyse the current conditions of these cells and take precautions to avoid health issues that it might cause.

Why Is the RDW Count Needed?

The RDW test is mainly conducted for anaemic patients, as a low RBC count fails to carry adequate oxygen through the blood. Doctors can pronounce a patient as anaemic after evaluating their current RBC count. In other cases, doctors suggest the RDW test as a part of a Complete Blood Count (CBC) test. This test measures various body parts, including the blood cells. It helps to diagnose the following health issues.

  • Heart diseases
  • Diabetes
  • Liver diseases
  • Cancer
  • Thalassemia
  • Weakness and fatigue
  • Dizziness
  • Family history of blood-related disorders
  • Pale skin
  • Chronic diseases (diabetes, HIV, or Crohn’s disease)
  • Diet with low vitamin B12, iron, etc.
  • Significant blood loss due to an injury

When Should I Get the RDW Test?

For many reasons, a physician may ask for a red cell distribution width (RDW) test, which is usually a part of a complete blood count (CBC) for different purposes:

  • Normal Blood Tests: These are an element of feature health check-ups or complete blood count (FBC) for all-around well-being monitoring.
  • Signs: Consult your physician for possible RDW tests if you experience any signs like fatigue, dizziness, weakness, shortness of breath or pale skin.
  • Chronic Illness: To help diagnose or monitor chronic illnesses such as anaemia and other blood disorders.
  • Treatment: Particularly in red blood cell production-related conditions, how well treatments work can be evaluated.

In conclusion, an RDW test is used to measure the variation in the size of red blood cells, which helps identify potential RBC-related health problems.

What is the Procedure for the RDW Test?

The RDW test is a simple blood examination usually done as part of a complete blood count (CBC). In this procedure, a medical professional will use a needle to take some small amount of your blood, mainly through your arm veins. These tests are referred to the laboratory for testing and obtaining results on RDW.

This test will determine the variation in the size of red blood cells. It is an easy and routine procedure that usually takes only a few minutes and does not require special preparation.

How Should You Prepare for the RDW Test?

Preparing for the RDW test is simple as it is part of a routine blood test requiring minimal preparation. Unless your healthcare provider advises otherwise, you can eat and drink normally before the test.

Nevertheless, ensure that you let your doctor know of any medications, supplements or health issues that you have since they may alter your results. If you are having RDW done as part of a full blood panel, your doctor might ask you to fast for some time.

Mostly, it’s not hard to prepare with its simplicity, thus making it convenient for most people with normal body checkups.

How to Measure RDW Count in Blood Test?

Now that you know what RDW in a blood test is, you must be curious about its procedure. Patients hardly have to undertake any preparation for taking only the RDW test. However, they might need to fast if there are other tests along with the RDW test. The process includes drawing blood samples from the patients.

The healthcare professionals then send the sample to their laboratories to analyse the RBC count. After collecting the details from the lab test, doctors divide the standard deviation (SD) of the mean corpuscular volume (MCV) by the MCV and multiply the result by 100 (RDW-SD)/(MCV)×100). It helps them to gain an understanding of the percentage value RBC size heterogeneity in the body.

How to Read Results of RDW in a Blood Test?

To understand the findings from an RDW test, one looks at the RDW value, which indicates how much red blood cell sizes vary. A greater degree of anaemia or other diseases can lead to higher values, indicating more differences in cell size among other vitamin deficiencies. A typical result means that most of your red cells are about the same size; this is healthy RBCs.

It is very important to consider the RDW value and how it relates to other blood tests, like haemoglobin or mean corpuscular volume (MCV) when interpreting RDW test results. The results of RDW are usually expressed in percentage terms with a normal range of between 11.5% and 14.5%. 

What Is a Normal RDW Count Range?

Now, you must be curious to know the normal range of RDW in a blood test. Most people consider an RDW count of 12%-15% normal and healthy. This percentage represents the amount of RBC count in the given blood sample. If your result displays this percentage, you are under no threat of having a blood-related disorder. However, you might need other medical tests to prove it further.

Here's a table with the parameters for the normal range of RDW based on age

S. No. Normal Range (RDW) Age
1 11.5% - 14.5% Adults (male and female)
2 12.0% - 15.5% Children (1-18 years)
3 12.5% - 16.5% Infants (up to 1 year)

Symptoms of High RDW

When RDW is high, it reflects variability in the size of red blood cells, which may be linked to various health conditions and indicates a possibility of potential issues like anaemia or nutritional deficiencies.

Symptom Description
Fatigue This often occurs when the oxygen-carrying capacity of blood is reduced, leading to persistent tiredness and lack of energy.
Dizziness It might result from low oxygen levels; thus, frequent lightheadedness or feeling faint may occur due to poor blood flow.
Shortness of Breath During physical activities, breathing can become difficult as the efficacy of red blood cells decreases, leading to reduced oxygen transport.
Pale Skin You can tell if someone has fewer red blood cells in their body by looking at them as they always have lighter skin tone than normal people.
Chest Pain With the heart working harder to supply oxygen all over the body, one will feel discomfort or pain in the chest.
Headaches Headaches can be caused by decreased oxygen reaching the brain, resulting in frequent or severe symptoms.
Rapid Heartbeat An increased pulse rate would attempt to compensate for the lower oxygen concentration in the body, trying to deliver more oxygen.
Cold Hands and Feet These extremities become cold occasionally due to ineffectiveness in circulation and poor oxygen levels.
Cognitive Impairment Trouble with memory, thinking straight, or loss of ability to know what is going on because there is not enough oxygen flowing through the brains
Weakness When muscles do not receive enough O2, they are vulnerable to generalised weakness and muscle fatigue.

What Does It Mean If Your RDW Count Is High?

If your blood test generated RDW count is higher than 15%, it means your RDW count is high.

Many reasons can be responsible for causing a high RDW count, such as high alcohol consumption. In addition, having a high RDW count can indicate developing the following conditions.

  • Hereditary spherocytosis
  • Chronic liver disease
  • Kidney disease
  • Valvular disease
  • Stroke
  • Colorectal cancer

Therefore, if you have a high RDW count, it is advisable to consult doctors and start further medical tests and treatments immediately.

What are the Causes of High RDW?

If your blood test-generated RDW count is higher than 15%, it means your RDW count is high. The following types of anaemia can cause a high RDW count.

Condition Description
Iron-deficiency Anaemia Iron deficiency leads to small and abnormal red blood cells, which in turn leads to increased RDW caused by variations in cell size resulting from low iron.
Macrocytic Anaemia This increase in RDW is often attributed to deficiencies in vitamin B12 or folate, which lead to the production of larger red blood cells, known as 'macrocytic'.
Microcytic Anaemia Iron deficiency or thalassemia can cause smaller RBCs. Consequently, there is an increase in the RDW because of differences in the sizes of RBCs that have reduced in size.
Haemolytic Anaemia It triggers premature lysis of red blood cells that stimulates the rapid production of new ones. This causes high RDW due to variations in the sizes of these cells.

Symptoms of Low RDW

Low red cell distribution width in the blood doesn't directly cause problems, but related conditions can impact your health. Here are a few symptoms of low RDW:

Symptom Description
Fatigue Chronic fatigue and low energy may be related to diminished oxygen-carrying capacity by blood cells.
Weakness Generalised weakness, making it hard to perform regular activities due to inadequate amount of red blood cells
Paleness Skin paleness denotes a shortage of haemoglobin or a decreased number of red blood cells that affects skin pigmentation.
Dizziness Dizziness and fainting are usually occasioned by reduced oxygen flow to the brain because there is not enough RCB.
Shortness of Breath Low oxygen levels in the blood that mostly cause breathing difficulties or shortness of breath.
Cold Hands and Feet A chill is experienced on the extremities due to poor circulation and reduced oxygen delivery to the hands and feet.
Headaches Regular or severe headaches occur when there is a reduced supply of oxygen to the brain due to anaemia.

What Does It Mean If Your RDW Count Is Low?

If your RDW is lower than 12%, it indicates a low RDW count. The meaning of low RDW blood test count usually refers to a normal situation. It means that your RBCs or red blood cells are uniform in size and shape. In such cases, these cells are likely to perform well for your body and reduce the chances of developing any blood-related disorders.

Thus, as you can see, RDW in a blood test can be essential to understanding the condition and functions of RBCs in the human body. However, high RDW means these cells are not uniform, resulting in future complications. Thus, if your RDW count is higher than normal, take proper consultations with the healthcare professionals and avoid future diseases.

What are the Causes of Low RDW?

Low RDW levels indicate that red blood cells are of similar size. This can be connected with various health problems. The following are common causes of low RDW:

Cause Description
Chronic Diseases Routinely, red blood cells are uniform in size due to conditions such as chronic liver disease, Crohn’s disease, diabetes, or HIV.
Nutritional Deficiencies Lack of important nutrients, especially iron or vitamin B12, may cause equal size of RBCs, leading to low RDW.
Bone Marrow Disorders Thalassemia and other disorders affecting haemoglobin production can produce RBCs whose sizes appear almost alike.
Blood Disorders For instance, macrocytic anaemia and microcytic anaemia lead to erythrocytes with uniform sizes, thus causing low RDW values.

Thus, as you can see, RDW in a blood test can be essential to understanding the condition and functions of RBCs in the human body. However, high RDW means these cells are not uniform, resulting in future complications. Thus, if your RDW count is higher than normal, take proper consultations with healthcare professionals and avoid future diseases.

FAQs about RDW in Blood Tests

Is high RDW serious?

It depends on your current health conditions. If you have other conditions triggering higher RDW, it might bring cardiovascular diseases and heart failure risks.

How can I lower my RDW count?

You can reduce your RDW count by limiting alcohol consumption, quitting cigarette smoking, eating a healthy diet and exercising regularly.

What does RDW stand for in a blood test?

RDW stands for Red Cell Distribution Width. It measures the variation in size of your red blood cells, indicating how much they differ in volume.

What is a normal RDW range?

The normal RDW range typically falls between 11.5% and 14.5%. This range can vary slightly depending on the laboratory and the age of the patient.

Why might my RDW levels be high?

High RDW levels may indicate various types of anaemia, vitamin deficiencies, or chronic diseases. It suggests significant variability in red blood cell sizes.

What are the symptoms of high RDW?

Symptoms of high RDW can include fatigue, weakness, pale skin, and shortness of breath. These symptoms often relate to underlying conditions affecting red blood cells.

What causes low RDW levels?

Low RDW levels are typically associated with chronic diseases, nutritional deficiencies, or specific blood disorders. It reflects a smaller variation in red blood cell sizes.

How is RDW tested?

RDW is measured with a blood sample as part of a complete blood count (CBC) test. It evaluates the distribution and variation in the size of red blood cells.

What does a low RDW indicate?

A low RDW indicates that red blood cells are more uniform in size. This condition can be related to chronic health issues or specific nutritional deficiencies.

Can diet influence RDW levels?

Yes, deficiencies in essential nutrients like iron and vitamin B12 can impact RDW levels. Maintaining a balanced diet is crucial for normal RDW values.

How often should I get an RDW test?

The frequency of RDW testing depends on your specific health condition and your doctor's recommendations. It may be part of routine monitoring or for evaluating particular health concerns.

What should I do if my RDW levels are abnormal?

If your RDW levels are abnormal, consult your healthcare provider for a comprehensive evaluation. Abnormal results often require further investigation of symptoms and other test results.

Does a high RDW always mean a serious condition?

Not necessarily. While a high RDW can suggest various health issues, it should be assessed in the context of other symptoms and test results to determine its significance.

Can RDW levels fluctuate?

Yes, RDW levels can fluctuate due to factors like hydration status or acute illness. Variations should be interpreted in conjunction with overall health and other test results.