What Level of RDW is Dangerously High? A Friendly Guide to Your Blood Test

Have you ever glanced at your blood test results and noticed the term RDW staring back at you, followed by a percentage? You’re not alone! Red Cell Distribution Width, or RDW, is one of those numbers that many people ignore—until it’s flagged as “high.” But what does a high RDW actually mean, and at what level should you start to worry?

Let’s Start with the Basics: What is RDW?

RDW stands for Red Cell Distribution Width. It’s a measure of the variation in size among your red blood cells. In other words, RDW tells your doctor how much your red blood cells differ from each other in size. Most healthy people have red blood cells that are roughly the same size, but certain health issues can cause them to become more varied.

Your RDW is measured as a percentage. The “normal” range is usually between 11.5% and 14.5%, but it can vary slightly from lab to lab. If your RDW falls outside that range, especially on the higher side, your doctor might want to investigate further.

So, What is Considered a High RDW?

Generally speaking, an RDW above 14.5% is considered high. But here’s where things get interesting: not all “high” RDW results are created equal.

If your RDW is only slightly above the normal range—say, 15%—it might not be cause for alarm, especially if the rest of your bloodwork looks fine. But when RDW levels start climbing significantly—into the 16%, 17%, or higher territory—it could signal that something more serious is going on.

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What Level of RDW is Dangerously High?

This is the million-dollar question. There isn’t a single “dangerously high” number that applies to everyone. However, most doctors start to get concerned when RDW exceeds 15.5%–16%, especially if you’re experiencing symptoms like fatigue, weakness, or unexplained bruising.

Important: A “dangerously high” RDW doesn’t mean you’re in immediate danger. It’s more of a red flag that something needs attention. Always talk to your doctor for personalized advice!

Extremely high RDW values—think 18%, 19%, or above—are rare and usually seen in people with serious health problems, such as advanced anemia, bone marrow disorders, or certain chronic illnesses. If your RDW is in this range, it’s likely your doctor will order more tests to figure out what’s going on.

What Can Cause a High RDW?

There are quite a few reasons your RDW might be elevated. Some are relatively harmless, while others require medical attention. Common causes include:

• Iron deficiency anemia: The most common cause. Your body makes oddly sized red blood cells when it doesn’t get enough iron.
• Vitamin B12 or folate deficiency: Both nutrients are needed for healthy red blood cells.
• Recent blood loss: After a major injury or surgery, your body churns out new cells at different sizes.
• Chronic illnesses: Things like liver disease or certain cancers can also cause RDW to rise.
• Inherited blood disorders: Conditions such as thalassemia or sickle cell anemia can lead to high RDW.

Occasionally, RDW may be temporarily elevated after an infection or during pregnancy, but these usually resolve on their own.

How is RDW Used with Other Blood Tests?

Doctors never look at RDW in isolation. It’s almost always interpreted alongside other blood markers, especially the Mean Corpuscular Volume (MCV). Here’s why:

• If both RDW and MCV are high, it could point toward vitamin B12 or folate deficiency.
• If RDW is high but MCV is low, it’s often a sign of iron deficiency anemia.
• If RDW is high and MCV is normal, things get a bit trickier—sometimes, it’s just an early warning sign that something’s starting to change.

What Should You Do If Your RDW is High?

First of all, don’t panic! A high RDW by itself doesn’t mean you have a serious disease. Here’s what to do:

• Talk to your doctor: They’ll look at the big picture—your symptoms, other test results, and medical history.
• Ask about follow-up tests: Your doctor might want to check your iron, vitamin B12, or folate levels, or look for signs of chronic illness.
• Consider your diet: Eating more iron-rich foods, leafy greens, and lean proteins can help if you’re low on certain nutrients.
• Don’t self-diagnose: Google is great, but it can also make you worry unnecessarily. Use it for information, not diagnosis!

Can You Lower a High RDW?

If your high RDW is due to a correctable cause—like a vitamin deficiency—then yes, you can often bring it back to normal with the right treatment. For example:

• Iron supplements or iron-rich foods for iron deficiency
• B12 or folic acid supplements for those deficiencies
• Treating any underlying chronic condition that’s affecting your blood cells

Sometimes, though, RDW remains high because of a chronic condition that can’t be easily reversed. In these cases, your doctor will help you manage the underlying problem as best as possible.

When Should You Worry About a High RDW?

The key is to pay attention to both your RDW and your symptoms. You should be extra cautious if:

• Your RDW is above 16% and steadily rising
• You’re experiencing symptoms like severe fatigue, shortness of breath, pale skin, or unusual bruising
• You have a family history of blood disorders
• Other blood test results are abnormal (especially your hemoglobin or MCV)

If any of these apply to you, it’s time to follow up with your doctor.

Key Takeaways

• Normal RDW is usually between 11.5% and 14.5%
• Above 15% is considered high; above 16% is cause for closer attention
• Very high RDW (18%+) is rare and often signals serious conditions
• RDW should always be interpreted in the context of other blood tests and your overall health
• If your RDW is high, don’t panic—just talk to your doctor

Remember, a blood test is a snapshot, not the whole story. Your doctor is your best resource for understanding what your numbers mean and what you should do next.