Have you ever taken your blood test report, that is, the 'Full Blood Count' (FBC) report that is usually written by the doctor, and got confused by the letters and numbers on it? There are names like MCV, MCH, PLT, RDW, one after another. You may not be able to figure out what these mean. Don't worry, many people feel that way. Today, let's understand in a very simple and conversational way what one important value in this report is, that is, what RDW is.
What does RDW simply mean?
Simply put, RDW stands for Red Blood Cell Distribution Width . In Sinhala, it means 'Red Blood Cell Distribution Width'. But don't get confused by that name. Let's understand this very easily.
Imagine that the red blood cells in your body are small red balls. These balls carry oxygen from our lungs to every part of the body, every organ. Just like gas cylinders. So, this oxygen is essential for every cell in the body to work and generate energy.
In a healthy person, these red blood cells are mostly the same size and shape . Just like a bunch of lemons from the store. There may be slight differences, but not a big difference.
The RDW test measures how much your red blood cells vary in size. That is, it checks whether all of your red blood cells are roughly the same size, or whether some are small, some are large, or whether they are of different sizes.
Despite the name 'Width', this does not measure the width of a blood cell. Instead, it measures the amount of variation in the size of blood cells.
A high RDW value means that there is a large variation in the size of the red blood cells. Some are very small, some are very large. A normal RDW value means that most of the red blood cells are the same size.
What is the relationship between the RDW test and the complete blood count (CBC)?
Your doctor will not order a test to check just the RDW. This is usually done as part of a complete blood count (CBC) . We also call this an FBC (Full Blood Count).
An FBC report provides information about the three main components of your blood:
- Red Blood Cells
- White Blood Cells
- Platelets
This FBC report has a special section that describes only red blood cells. It is called RBC Indices.RDW is one of those RBC Indices. Let's look at the main values in this section.
| Test name (RBC Index) | What is simply measured? |
|---|---|
| RDW (Red Cell Distribution Width) | Measures the size variation of red blood cells. |
| MCV (Mean Corpuscular Volume) | The average size of a red blood cell is measured. |
| MCH (Mean Corpuscular Hemoglobin) | It measures the amount of hemoglobin normally contained in a single red blood cell. |
| MCHC (Mean Corpuscular Hemoglobin Concentration) | How is the concentration of hemoglobin inside a red blood cell measured? |
When a doctor examines your medical condition, especially a condition like anemia, they look at all of these values together. They don't make a decision based on just one value.
When is an RDW test needed?
If you have symptoms that suggest you have anemia, your doctor may order an FBC test. This will also check your RDW value. Anemia is when you don't have enough healthy red blood cells to carry oxygen around your body.
Symptoms that may suggest anemia
If you have symptoms like these, it is important to seek medical advice:
- Constant feeling of extreme fatigue
- Shortness of breath even when walking a little
- Feeling cold all the time
- Dizziness or lightheadedness
- Pale or dry skin
- FrequentHeadache
Medical conditions that can cause an elevated RDW value
The RDW test, along with other RBC indices, can help determine the cause of anemia. There are many different causes of anemia.
- Vitamin and mineral deficiencies: Anemia, especially caused by iron, vitamin B12, and folate deficiencies, can cause an elevated RDW value.
- Thalassemia: This is a genetic condition.
- Chronic illnesses: Long-term conditions such as diabetes, Crohn's disease, and HIV.
- Kidney or Liver disease
- Cancer
- Cardiovascular disease
- Severe bleeding from an accident or surgery.
How is this RDW test done? Is it something to be afraid of?
Not at all. This is just a very simple, routine blood test. It takes just a few minutes.
There is nothing special you need to prepare for before your blood draw. However, if your doctor has ordered another test, such as a fasting blood sugar test, along with the FBC, you will need to fast for a specific number of hours. Your doctor will advise you on this.
This is what happens when blood is drawn:
1. A nurse or doctor will find a good vein near your elbow or on the back of your hand.
2. Clean the needle insertion site thoroughly with an alcohol swab.
3. A rubber band (like a tourniquet) is tightened slightly above the needle insertion point to help the vein emerge better.
4. The needle is then inserted into the vein and the required amount of blood is collected in a small vial. You may feel a slight stinging sensation as the needle is inserted.
5. Once the blood is drawn, the needle is removed, a piece of cotton is placed on the site, and a small plaster is applied.
You can usually leave immediately after giving blood. Sometimes you may feel a little dizzy, but you will be asked to sit for a few minutes. The area where the needle was inserted may be slightly blue, but this will go away on its own in two to three days. This is a very safe test.
How to understand RDW results?
Your RDW value is shown as a percentage (%). Let's see if that value is normal, high, or low.
| Result | Meaning |
|---|---|
| Normal RDW | This means that your red blood cells are mostly the same size. The RDW value is usually between 12% and 15% . However, these values can vary slightly depending on the lab that performs the test. The normal range for that lab is mentioned on your report. Important: If the RDW is normal, but another value (such as MCV) is abnormal, it may also indicate a medical condition. |
| High RDW | This means that there is a wide variation in the size of red blood cells. Some are small, some are large. This can be a sign of anemia or another related condition. The RDW value is especially high in anemia caused by iron deficiency. The doctor will compare the RDW value with the MCV value to reach a conclusion. |
| Low RDW | An RDW value that is lower than the normal range is usually nothing to be concerned about. It is not associated with any specific medical condition. |
Very important: Do not assume that you have a disease based on whether your RDW is high or normal. RDW is only one piece of a larger puzzle. Your doctor will use the other values in the FBC report, your symptoms, and other tests, if necessary, to make an accurate diagnosis.
Once you receive the blood report, take it to your treating doctor and discuss it clearly. Ask him or her any questions or concerns you may have.
Take-Home Message
- RDW (Red Blood Cell Distribution Width) is a test that measures the variation in the size of your red blood cells.
- This is usually done as part of a complete blood count (FBC/CBC).
- An elevated RDW value may be a sign of anemia, but it alone is not sufficient for a diagnosis.
- A decrease in RDW value is usually not a cause for concern.
- Once you receive your blood test report, always discuss the results with your doctor, rather than jumping to conclusions on your own.
👩🏽⚕️ Additional questions (FAQs)
💬 What is the 'MCH Blood Test' in the blood report (FBC/CBC)? How is it related to RDW?
The 'MCH (Mean Corpuscular Hemoglobin)' in your Full Blood Count (FBC) is the 'amount of Hemoglobin' (the iron protein that gives blood its red color and carries oxygen) inside one of your red blood cells (RBC). The 'RDW' in your article is the 'variability of size/dimensions' of blood cells. It is by taking these two values (MCH and RDW) together that doctors can determine exactly what type of anemia you have!
💬 Why is my MCH value abnormally low (Low MCH) in my report? Is it dangerous?
A 'low MCH' value (usually less than 27 picograms) means that your blood cells are lacking iron (the blood cells are pale). The main and number 1 cause of this is 'Iron Deficiency Anemia' - not enough iron in the body to produce blood properly! In addition, genetic blood diseases like Thalassemia can also show a very low MCH value.
💬 If the MCH/Hemoglobin in the blood report is low, what are the fatal cases that require immediate hospitalization/blood transfusion?
This can be corrected in a few months by taking iron pills. But the biggest danger! 1) If this blood loss causes you to have 'Chest pain / Angina', 2) If you are constantly dizzy and lose consciousness, 3) If your heart rate is abnormally fast, your heart may not get enough oxygen and your heart may stop (Heart failure)! You need to be hospitalized immediately!
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