What Is RDW Blood Test? What Does It Mean In CBC Test?

RDW stands for red blood cell distribution width. RDW blood test is one of the most basic tests that helps to assess the red blood cells in the body that transport oxygen from the lungs to the body tissues and carry back carbon dioxide to the lungs. The RDW test measures variation in the volume and size of RBC. Proper width and volume of RBC is very crucial for oxygen transport, clot prevention and overall health. So maintaining a normal volume and diameter of RBC is very important. RBC maintains a diameter ranging between 6.2 to 8.2 micrometers. However, a variation of RDW may be seen in the cases of several anemias, vitamin deficiencies or certain health conditions. RDW can be elevated if there is a wide variation in red blood cell sizes. In other words, if your average RBCs are small but many are even smaller or RBCs are large but many are even larger, this variation in size can cause your RDW to be elevated. The normal RDW value typically ranges from 11.5-14.5%.

RDW plays a crucial role in understanding the mean corpuscular volume (MCV) values and the health of your circulatory system. RDW blood test doesn't interpret a complete blood count (CBC) rather it is a test that may be used to diagnose anemia or other health conditions.

What Does The RDW Test Reveal About Your Health?

RDW test is generally performed as a part of the CBC test. A complete blood count measures different components of your blood including RBCs, WBCs, Hgb, Hct, platelets etc. The RDW value in your CBC test helps to understand the variation in size of your red blood cells and helps to diagnose several types of anemia including:

• Iron deficiency anemia 

• Hemolytic anemia 

• Aplastic anemia 

• Vitamin B12 or Folate deficiency anemia

• Nutritional deficiency anemia 

RDW test also helps to differentiate between types of anemia and their causes. However, the doctor may also check your RDW value if you have:

• Nutritional deficiencies 

• Chronic inflammation 

• Cardiovascular diseases

• Symptoms of anemia 

• Serious illness 

• Family history of blood diseases

• Or to monitor your treatment response 

Besides, the RDW test also assists in diagnosing:

• Diabetes mellitus 

• Kidney diseases

• Bone marrow disorders 

• Heart diseases

• Hyperthyroidism 

• Cancer 

• Thalassemia 

How To Do The RDW Test?

RDW blood test is associated with the measurement of the variation in size(volume) of RBCs. It is tested as a part of a complete blood count (CBC) test and the RDW value is an indicator of various health conditions like anemia. Although the RDW test is not a separate test, some procedures can be followed to draw a better result.

There is no special preparation required to perform the test. However, the patient may fast for 2-4 hours before the test to ensure accurate results. Some blood substances may become affected by the intake of food. Patients may also mute the taking of some medications that can alter the test results. 

The sample of blood is collected by a healthcare professional by applying a tourniquet to the upper arm. The healthcare professional inserts a needle into the vein and collects blood into a sealed tube. The collection method of the sample blood is very quick and easy. 

After collected, the sample is sent for laboratory analysis. The analyzer checks the size and distribution of the red blood cells and calculates the RDW. The final result is displayed on the report of the test. The normal RDW ranges typically from 11.5% to 15%.

When To Do An RDW Test?

As mentioned before, the RDW (red cell distribution width) is tested as a part of a complete blood count test. The RDW helps to assess the variation in size and volume of red blood cells. However, a physician may ask you to perform an RDW test as a part of regular health checkups or if he observes:

Symptoms of anemia-

• weakness 

• dizziness 

• headaches 

• arrhythmia

• chest pain

• shortness of breath 

• pale skin 

Your physician may also ask for RDW to differentiate the types of anemia while RDW is useful to interpret mean corpuscular volume. Besides, your healthcare provider may need an RDW test to-

• Evaluate nutritional deficiencies 

• Monitor response to treatment 

• Investigate chronic diseases 

• Routine health checkup 

Normal RDW Range

The normal RDW value indicates that your red blood cells (RBCs) are similar in size and volume. The normal diameter of RBCs ranges between 6.2-8.2 micrometers. The RDW value is presented as the percentage of blood cells that indicates how many red blood cells in a given sample deviate from the average size and volume. Generally, the average RDW value ranges between 11.5% to 15%. However, this range may vary depending on the labs performing the test. This reference range is the same for both genders. A value greater than 14.5% is called high RDW while a value lower than 10.2 is considered as low RDW. The fluctuations in the size of RBCs from the natural range indicate several anemias and health conditions.

Can RDW Change Over Time?

RDW is not a static value. It can fluctuate over time due to various reasons. If any factor affects the production and destruction of red blood cells, it can influence the RDW value. Various factors are identified which can affect the RDW value. But interestingly, RDW tends to increase with aging. Factors influencing the RDW value are discussed below:

• Age: RDW elevates with the increase of age. But the reason behind this elevation is unknown.

• Medical Conditions: Several nutritional deficiencies can hamper the production of RBCs and cause an increase in RDW. Besides, other hemolytic diseases and excessive blood loss can be a reason. 

• Disease Progression: Some chronic diseases like liver disease, heart failure or kidney diseases especially in geriatric patients can interfere with the production of RBCs, hence can change RDW.

• Diet: Diet can also influence RDW as insufficient nutrition cannot help production of RBCs properly, and poor diet can cause elevation of RDW. Other dietary factors like smoking also influence RDW.

Abnormal RDW And Interpretation

High RDW 

A high RDW indicates that red blood cells in a given sample deviate significantly from the average size and volume. The condition is also known as anisocytosis. A high RDW is generally associated with various nutritional deficiencies, anemia or other chronic diseases. Some common causes of elevated RDW are:

• Nutritional deficiencies 

• Iron deficiency anemia 

• Vitamin B12 or folate deficiency anemia 

• Heart diseases 

• Chronic kidney disease 

• Diabetes etc

A patient may also develop elevated RDW because of recent blood loss(hemorrhage)as the body produces new varied-sized RBCs to compensate which can significantly elevate the RDW value. 

The normal RDW ranges between 11.5 to 14.5%. Yet some labs might consider slightly different ranges as normal. 

A general interpretation of high RDW and their causes are given below:

RDW vs Other CBC Parameters 

RDW is one of the several parameters in a complete blood test that provides information about the fluctuations of red blood cells from the normal size and shape. CBC is a fundamental blood test that provides a comprehensive overview of your blood health and helps to diagnose a wide range of medical conditions. CBC measures and calculates several parameters alongside the RDW.

A comparison of RDW and other key parameters of CBC:

RDW and MCV Combination 

RDW and MCV(Mean Corpuscular Volume) parameters both are measured in a complete blood count test. RDW states the deviation in size and volume of red blood cells. The average RDW is 11.5-14.5%. On the other side, MCV measures the average size(volume) of red blood cells. The average MCV is 80-100 fL. Like RDW, MCV is also significant as it can help to diagnose several anemias and deficiencies. A higher MCV indicates that red cells are larger than normal and low MCV indicates that cells are smaller than normal red blood cells. Low MCV and high MCV can individually predict some anemias or diseases.

• Low MCV → Iron deficiency anemia, thalassemia 

• High MCV → Folate deficiency anemia, liver disease 

But if the value of MCV is interpreted together with RDW, types of anemia and other diseases can be diagnosed more accurately. 

Combination of MCV and RDW:

• High RDW+High MCV → Vitamin B12 or folate deficiency anemia 

• High RDW+Low MCV → Iron deficiency anemia 

• Normal RDW+Low MCV → Thalassemia 

• Normal RDW+High MCV → Liver diseases

RDW-CV vs RDW-SD 

RDW-CV(Coefficient of Variation) and RDW-SD(Standard Deviation) both are the measurement of variation of red blood cells. RDW-CV means the percentage of variation in size of RBCs where RDW-SD shows the width of red blood cells. RDW-CV means the range of variation and RDW-SD tells the exact range of size of RBCs. Range of RDW-CV is expressed in percentage(%) where RDW-SD is expressed in femtoliter(fL) unit. 

Some key differences of RDW-CV and RDW-SD are given below:

RDW In Diagnosing Anemia And Diseases

How Does RDW Help In Diagnosing Anemia?

RDW can not diagnose anemia alone but when interpreted with other CBC parameters, it can provide valuable clues to identify the type, causes and severity of anemia. RDW can help in classifying anemia by measuring the variation in size of the RBCs. Some features of how RDW helps in the diagnosis of anemia are discussed below:

• RDW helps to distinguish between different types of anemia based on the uniformity and size of the RBCs.

Interpretation:

High RDW+ Mixed-size RBCs — Iron deficiency.

• When combined with MCV (Mean Corpuscular Volume) it becomes a powerful diagnostic tool and helps pinpoint specific types of anemia.

Example: 

High RDW+ Low MCV — microcytic anemia 

High RDW+ High MCV — macrocytic anemia 

• Combination with MCV also helps to detect nutritional deficiency anemia.

Example:

High RDW+ Low MCV — iron deficiency anemia 

• RDW test helps to monitor the progress of anemia treatment 

• RDW also helps to differentiate iron deficiency and thalassemia.

RDW And Iron Deficiency Anemia 

Iron deficiency is a condition of the body when the body lacks enough iron to produce hemoglobin leading to decreased oxygen transport throughout the tissues. There may be several causes of anemia: 

• Inadequate intake of iron

• Increased iron need (pregnancy, adolescence)

• Heavy blood loss

• Poor absorption of iron due to chronic diseases 

However, RDW is a great determiner of iron deficiency anemia. How RDW reflects iron deficiency anemia in the body is described -

• In the early stage of iron deficiency anemia, the body starts to produce small RBCs, but yet some stay as normal which increases RDW.

• If the MCV level decreases, it strongly suggests iron deficiency anemia.

• If the ferritin is low, then the iron deficiency is confirmed.

Besides predicting anemia, RDW helps to distinguish between iron deficiency anemia and thalassemia.RDW is useful also in the tracking of recovery of anemia.

Tracking of Iron Deficiency Anemia

RDW And Vitamin B12 Deficiency Anemia 

Vitamin B12 deficiency anemia occurs when the body fails to produce healthy RBCs due to inadequate amounts of vitamin B12. Vitamin B12 is a crucial element for proper red blood cell development. Generally, the red blood cells are uniform in size. But without adequate vitamin B12, the bone marrow produces abnormally large, immature red blood cells which leads to elevated RDW. The premature RBCs don't function properly and die prematurely. This type of anemia is called megaloblastic anemia. 

Relationship between vitamin B12 and RDW:

(RDW is a common finding in vitamin B12 deficiency anemia)

• Dissimilar red blood cell production: 

Due to a deficiency of vitamin B12, our body struggles to produce RBCs of uniform size and shape causing the production of larger-than-normal and smaller sizes of RBCs that are reflected as elevated RDW.

• Distinguishing anemia types:

RDW is a very strong tool to determine different types of anemia.

High RDW+ High MCV→ This combination suggests vitamin B12 deficiency anemia 

High RDW+ Normal MCV → indicates nutritional deficiency anemia (including vitamin B12)

RDW And Thalassemia 

Thalassemia is a disorder characterized by reduced production of one or more globin chains in the blood leading to inadequate or abnormal production of hemoglobin, immature red blood cell production and premature destruction. It is often complex to identify and differentiate thalassemia from other types of anemia, especially iron deficiency anemia. RDW is a useful parameter to distinguish thalassemia from other types of anemia.

RDW in the identification of thalassemia:

In mild forms of thalassemia, red blood cells become smaller than normal (microlytic) leading the RDW from normal to mildly elevated. This is because of the deflection in globin chain production which leads to a uniform production of small cells. This "uniform smallness" is the key determining factor of thalassemia.

RDW In Chronic Diseases 

RDW is a parameter in CBC that quantifies the variation in size and volume of red blood cells. It presents the deviation of the size of RBCs from the normal size range. Chronic diseases and mental stress can affect the production of red blood cells (erythropoiesis). As a result, the bone marrow produces premature and irregular RBCs that are not uniform in size and shape. This difference in size causes elevated RDW. Hence RDW is increasingly considered as a useful marker for adverse outcomes of several chronic diseases. RDW is not a standalone parameter to diagnose diseases. Healthcare professionals conjugate RDW with other CBC parameters to diagnose diseases. Elevated RDW value may indicate worsening health conditions and nutritional deficiencies. RDW values in some chronic diseases are given:

• Heart disease: Elevated 

• Chronic kidney disease: Frequently elevated 

• Anemia: Normal or mildly elevated 

• Heart failure: Strongly elevated 

• Cancer: Elevated 

RDW value can be abnormal in case of other chronic diseases like diabetes, liver disease, HIV, autoimmune diseases etc.

RDW And Inflammation 

RDW(Red Blood Cell Distribution Width) reflects the variation in size and distribution of RBCs. RDW has been shown to be associated with inflammation in various chronic diseases. Its linking with inflammation can be of two types. 

Firstly, it can be an adverse outcome of any inflammatory conditions in the body. Inflammation can disrupt the production of red blood cells(erythropoiesis) and influence in production of irregular blood cells leading to elevated RDW. 

Secondly, RDW can act as an inflammatory marker. Nowadays, RDW is increasingly being considered as a potential inflammatory marker whereas the other inflammatory markers are becoming less informative. Studies have shown an association of RDW with various inflammatory diseases. An elevated RDW can be a potential marker for these diseases. 

RDW And Cancer 

Red blood cell distribution width (RDW) is a clinical parameter used to diagnose and monitor treatment effects in various types of anemia and chronic diseases. RDW is associated with various human diseases including cardiovascular disease, thrombosis, liver disease, kidney failure etc. Some recent research strongly suggests that RDW is associated with mortality from various cancers. Considering the poor prognosis of cancer, RDW is considered an effective clinical predictor of cancer with great significance. However, RDW can predict the mortality of various cancers including lung cancer, stomach cancer and colon cancer. Nonetheless, recent evidence has shown a positive correlation between RDW and cancer mortality which states that higher RDW associated is with an increased risk of cancer mortality. Hence, RDW can be used as an indicator to predict the mortality of tumors and the risk assessment of cancer patients.

Special Situations And Management

RDW In Children 

The typical range of RDW in children is usually similar to adults. In children, RDW-CV ranges between 11.5-15% and RDW-MV ranges between 37-54 fL. RDW is a vital diagnostic marker that in children, can help early detection of several nutritional deficiencies. Treating deficiencies in the early stage supports optimal physical development and improves a child's IQ (Intelligence Quotient) and cognitive performance. Deficiency in early childhood may cause delayed brain maturation, poor memory and poor learning skills. Besides, any hidden health issues can be revealed in the RDW test. Premature babies have more iron demands. So, monitoring the RDW is essential to meet the children's nutritional demands properly.

Risks Of RDW Test 

RDW is a part of the complete blood count which is a low-risk blood test. It's just a simple blood draw having minor risk factors. 

Some temporary effects may be observed during or after the blood collection process -

• Dizziness 

• Mild pain

• Mild bruising 

• Bleeding 

• Scarring or vein damage 

• Vein irritation etc.

What Are The Next Steps If RDW Results Are Invalid?

There are several factors responsible for abnormal RDW. If you have abnormal RDW, your next move will be to find and treat the underlying causes affecting the RDW. At first, you should take an overview of your CBC test as RDW is not a standalone parameter to diagnose a disease. An overview of the CBC report will give you an idea about the problem you're having. Then you should conjugate the RDW and MCV values to figure out the possible causes. If needed, perform additional tests based on the findings of conjugation (e.g. if you find iron deficiency perform serum ferritin or serum iron test. If folate deficiency is suspected, perform serum vitamin B12 or serum folate test in a diagnostic center). Perform clinical correction and analyze your family history to find the exact underlying cause behind your abnormal RDW. Lastly, treat the underlying cause with medications, intake of supplements or proper dieting. 

Steps If RDW Results Are Invalid

Can Diet Affect RDW?

Diet is one of the major factors regulating the RDW value. Improper diet with nutrient deficiencies can lead to altered RDW.

Detailed Explanation:

A diet lacking nutrient elements causes the body to produce red blood cells of irregular sizes leading to several nutrition deficiency anemia. Some are discussed below-

• Iron Deficiency Anemia: This type of anemia is caused by Inadequate absorption of iron in the body. It hinders the production of hemoglobin which carries oxygen. This inadequate production of hemoglobin causes the production of smaller, less developed RBCs which causes elevated RDW.

• Vitamin B12 Deficiency Anemia: Poor dietary habit and impaired absorption of vitamin B12 causes macrocytic red blood cell production and lead to elevated RDW.

• Folate Deficiency Anemia: This anemia type is similar to vitamin B12 deficiency anemia and causes megaloblastic changes in bone marrow.

Lifestyle Habits To Maintain A Normal RDW Level

The treatment of abnormal RDW varies from person to person, case to case. However, a doctor can suggest a general guideline to maintain a normal RDW state. Leading a lifestyle with proper guidelines is essential to maintain a normal RDW. One can follow these guidelines:

01. Intake of Balanced Diet: A diet rich in nutrients and supplements is essential to avoid the chances of several deficiency anemias that influence the RDW value. Proper dieting is required to produce healthy red blood cells which can help to reduce the chances of elevated RDW. 

02. Avoid Chronic Stress: Stress can interfere with the absorption of nutrients which may elevate the RDW. Avoid overthinking, and practice yoga or medications daily. 

03. Quit Smoking: Smoking can trigger the RDW elevation. So quitting smoking is a better way to maintain normal RDW.

04. Avoid Alcohol: Alcohol can destroy the red blood cells. If the production of RBCs is hampered, immature RBCs are produced and RDW gets elevated which causes several heart diseases or complications.

05. Stay Hydrated: Dehydration can alter the blood volume and plasma concentration causing an alteration in RDW value. Aim for drinking 2-3 liters of water daily.

06. Exercise: Daily exercise maintains proper blood circulation and proper production of red blood cells which is also important in maintaining normal RDW.

07. Sleep: Some recent surveys claim that adequate sleep (6-8 hours) helps to maintain RDW in the normal range.

Frequently Asked Questions(FAQs)

1. What does a low RDW indicate?

A low RDW means that there is minimal variation in the size of RBCs which means RBCs are relatively uniform in size.

2. Is the RDW test included in a routine blood test?

Yes, RDW is one of several parameters in CBC that demonstrates the rate of fluctuation in the size of red blood cells.

3. What are the factors that affect RDW?

Several factors like nutrient deficiencies, chronic diseases, diet, age, and genetics can affect the RDW.

4. What is the significance of the RDW test?

RDW is a clinical diagnostic parameter that helps to diagnose several deficiency anemias and other health issues.

5. What happens if RDW is higher?

High RDW means a significant variation in the size of RBCs which indicates potential diseases like anemia, liver diseases or cardiovascular issues.

6. How to reduce RDW value?

A balanced diet, adequate sleep, avoiding alcohol, and daily exercise are some general guidelines for maintaining a normal RDW.

7. What is an alarming RDW count?

The normal RDW range is 11.5-14.5%. An above 14.5% RDW count is generally considered to be an alarming value. 

8. Can infection increase RDW?

Yes, infections can alter the production of RBCs and lead to elevated RDW.

9. Can dehydration cause high RDW?

Dehydration affects blood circulation and plasma concentration which can indirectly alter the production of RBCs and cause high RDW.

10. Can you have normal hemoglobin with a high RDW?

Yes, it is possible to have a normal hemoglobin with a high RDW.

11. Is high RDW genetic?

Yes, a large(29%) number of patients have inherited high RDW genetically.

12. Is 17.1% high for RDW?

Yes, an RDW count over 14.5% is considered to be a high RDW.