Red Cell Distribution Width (RDW)
About Red Cell Distribution Width (RDW) Test
| Field | Value |
|---|---|
| Also Known As | RDW-CV (Coefficient of Variation), RDW-SD (Standard Deviation), Erythrocyte Distribution Width |
| Sample Type | Whole blood |
| Fasting Required | No fasting required |
| Report Time | Within 1 day |
| Recommended For | All genders and ages |
| Price | Starting at ₹120 |
What Is a Red Cell Distribution Width (RDW) Test?
The Red Cell Distribution Width (RDW) test measures how much red blood cells vary in size. Red blood cells carry oxygen throughout your body, and significant variation in their size can signal certain health conditions.
Doctors often order the RDW test or the RDW-SD test as part of a Complete Blood Count (CBC) or when investigating symptoms related to anemia or blood disorders. A small blood sample drawn from a vein in your arm is all that is needed.
What Does a Red Cell Distribution Width (RDW) Test Measure?
The RDW test reports two values that describe the degree of size variation among your red blood cells. Here is what each one tells you:
| Parameter | What It Measures | Unit |
|---|---|---|
| RDW-CV (Coefficient of Variation) | Size variation of red cells relative to their average size | % |
| RDW-SD (Standard Deviation) | Absolute spread in red cell size; useful for spotting mixed cell populations | fL (femtolitres) |
Together, these two values give doctors a clearer picture of red blood cell health than either figure alone.
Why Is a Red Cell Distribution Width (RDW) Test Done?
Doctors request an RDW blood test when they want to investigate symptoms that may point to anemia or related conditions. Below are the situations in which this test is most commonly ordered.
Common Symptoms That May Require This Test
The following symptoms are typical reasons a doctor may recommend this test:
- Persistent tiredness or fatigue with no obvious cause
- Unusual weakness or lack of energy
- Pale skin or pale inner eyelids
- Shortness of breath during light activity
- Dizziness or light-headedness
- Cold hands and feet
- Brittle or fragile nails
Conditions This Test Can Help Detect
The RDW test helps identify a range of blood and systemic conditions, including:
- Iron deficiency anemia (a raised RDW distinguishes it from thalassaemia, which typically shows a normal RDW)
- Megaloblastic anemia caused by vitamin B12 or folate deficiency
- Chronic inflammation and liver disease
- Mixed anemia and bone marrow disorders
- Cardiovascular conditions, chronic kidney disease, and chronic obstructive pulmonary disease
Red Cell Distribution Width (RDW) During Pregnancy
Iron deficiency anemia is common during pregnancy and can develop before hemoglobin levels fall noticeably. Because red blood cell size changes earlier than other markers, the RDW can flag early iron deficiency before other tests turn positive. Monitoring hemoglobin, red cell indices, including RDW, and serum ferritin usually starts at the first prenatal visit or during the first trimester.
Red Cell Distribution Width (RDW) for Chronic Disease Monitoring
In patients with chronic conditions such as rheumatoid arthritis, an elevated RDW may reflect ongoing disease activity and can help track how well treatment is working. Doctors also use repeated RDW measurements to monitor patients on hemodialysis receiving erythropoietin therapy, where shortages of iron, vitamin B12, or folate are common. Tracking changes in RDW over time gives useful information about a response to their treatment plan.
How to Prepare and What to Expect
No special preparation is needed for the RDW test procedure. The sections below cover what to keep in mind before and during sample collection.
Do You Need to Fast?
No, fasting is not required for this test. You can eat and drink as normal before your appointment. If your doctor has ordered additional tests alongside the RDW, check whether any of those require fasting.
Practical Tips Before Your Test
Keeping these points in mind will help ensure a smooth experience:
- Drink water as you normally would; being well-hydrated makes vein access easier.
- Tell your doctor or phlebotomist about any medicines or supplements you are currently taking.
- Wear a short-sleeved or loose-sleeved top for easy access to your arm.
- Avoid strenuous exercise or high stress immediately before the test, as these can influence results.
Step-by-Step Procedure
The blood collection process is quick and straightforward. Here is what to expect:
- The phlebotomist selects a suitable vein, usually at the crook of your arm or the back of your hand, and cleans the area.
- An elastic band is placed above the site to slow blood flow, making the vein easier to locate.
- A small needle is gently inserted and approximately 2 ml of blood is collected into a lavender-top EDTA tube.
- Once enough blood is drawn, the needle is removed and a small bandage is placed over the spot.
- The entire process usually takes less than five minutes and causes minimal discomfort.
- Your sample is labelled and sent to the laboratory, where it is stored and processed under controlled conditions.
Factors That Can Affect Accuracy
A few factors can influence the reliability of your RDW test result:
- Very high white blood cell counts, which can interfere with red blood cell measurements
- The presence of large immature red blood cells (reticulocytes)
- A recent blood transfusion, which introduces donor cells of different sizes
- Poor sample handling or storage conditions
- Ongoing infections or acute inflammatory states
Understanding Your Red Cell Distribution Width (RDW) Results
Your doctor will review your RDW result alongside other red cell indices and your overall clinical picture. The table below shows the general reference ranges used by most laboratories.
| Parameter | Normal Range | Possible Concern If High | Low Value |
|---|---|---|---|
| RDW-CV | 11.5% to 14.5% | Greater than 14.5% | Below 11.5% (rarely significant) |
| RDW-SD | 39 to 46 fL | Above 46 fL | Below 39 fL (rarely significant) |
A low RDW simply means your red blood cells are very uniform in size. This is not a sign of anemia and is considered clinically insignificant in most cases. A high RDW suggests greater variation in cell size, which can point to nutritional deficiencies, mixed anemia, or other conditions described above.
These ranges are general guidelines. Your doctor will interpret your results based on your age, health history, and other factors. Always consult a qualified healthcare professional for personalised medical advice.
Results During Special Conditions
Several factors beyond anemia can push RDW values outside the normal range. Older age, diabetes, cardiovascular disease, gastrointestinal disorders, and a range of inflammatory conditions are all associated with elevated RDW. Additionally, pregnancy causes physiological changes in blood volume that may alter RDW readings, and recent blood transfusions can temporarily shift values by introducing donor red blood cells of varying sizes.
How to Maintain Healthy Levels
Supporting red blood cell health through everyday habits is straightforward:
- Eat a diet rich in iron (leafy greens, legumes, lean meat), vitamin B12 (eggs, dairy, fish), and folate (beans, lentils, dark vegetables) to avoid nutritional deficiencies that can raise RDW.
- Reduce or avoid smoking and alcohol, both of which are linked to increased red blood cell size variation.
- Aim for regular physical activity and adequate sleep to support overall blood health.
Lupin Diagnostics Red Cell Distribution Width (RDW) Price and Home Collection
The RDW test cost at Lupin Diagnostics starts at ₹120, and home sample collection is available across cities in India. The indicative city-wise prices are listed below.
| City | Approximate Price (₹) |
|---|---|
| BHOPAL | 120 |
| CHENNAI | 150 |
| HYDERABAD | 120 |
| KOLKATA | 150 |
| NAVI MUMBAI | 120 |
| PUNE | 120 |
Prices are indicative and may vary by location. Please confirm the current price at the time of booking.
How to Book
Booking your RDW test online is simple:
- Select the Red Cell Distribution Width (RDW) test on the Lupin Diagnostics website.
- Choose your city and preferred time slot.
- Opt for home sample collection by a certified phlebotomist, or visit your nearest Lupin Diagnostics centre.
- Receive your report via email or WhatsApp within 1 day.
Home Collection
RDW test home collection is available across cities through Lupin Diagnostics. A certified phlebotomist visits your home at your chosen time to collect the blood sample. All samples are processed in NABL-accredited laboratories, and your digital report is accessible via email or WhatsApp once ready.
Frequently Asked Questions
The Red Cell Distribution Width (RDW) test measures how much red blood cells differ in size. Doctors use it alongside other red cell indices, particularly mean corpuscular volume (MCV), to investigate the possible causes of anemia and other blood disorders. It is often part of a routine Complete Blood Count (CBC).
No fasting is needed before this test. You can eat and drink as normal before your appointment. If your doctor has ordered other tests at the same time, check whether those have any specific preparation requirements.
A high RDW means your red blood cells vary considerably in size. This is often linked to iron, vitamin B12, or folate deficiency, mixed anemia, or recovery after blood loss. Your doctor will look at the result alongside other parameters to identify the underlying cause.
No. A low RDW simply means your red blood cells are very similar in size. It is not considered a sign of anemia or any underlying condition, and doctors do not usually use a low RDW alone to diagnose any illness.
Yes, it can provide early signals. In iron deficiency anemia, red blood cell size variation tends to increase before hemoglobin levels fall outside the normal range. An elevated RDW can therefore prompt further investigation before other markers become abnormal.
Results are typically available within 1 day of sample collection at Lupin Diagnostics. You will receive your report digitally via email or WhatsApp.
Yes, RDW test home collection is available. A trained phlebotomist will visit your home at your selected time to collect a small blood sample. The sample is then transported to a NABL-accredited Lupin Diagnostics laboratory for testing.
Red Cell Distribution Width (RDW)
