Introduction
When your doctor orders a blood test, one of the values often reported is the RDW, short for Red Cell Distribution Width. It measures the variation in size of your red blood cells. For many people, RDW is just another confusing number in a long list of results, but in fact, it can be an important clue about your overall health.
A common question that arises is: what level of RDW is dangerous? The answer isn’t always straightforward. RDW by itself doesn’t give a complete picture, but extremely high or low levels can indicate underlying health problems ranging from anaemia to more serious conditions like cardiovascular disease.
In this article, we’ll break down everything you need to know about RDW levels: what’s normal, when it becomes concerning, and how it links to your health. By the end, you’ll know not only what your blood test means, but also when you should follow up with your doctor.
What Is RDW?
RDW stands for Red Cell Distribution Width. It measures the range of sizes and volume of your red blood cells. Ideally, your red blood cells should be relatively uniform in size because that ensures efficient oxygen transport.
- Low variation = healthier red blood cells.
- High variation = possible problem with production or destruction of red blood cells.
A standard RDW value is usually reported as a percentage. Most laboratories consider a normal RDW range to be between 11.5% and 14.5%.
What Level of RDW Is Considered Dangerous?
The real concern begins when your RDW falls outside the standard range.
- Mildly elevated RDW (15–16%) → may suggest iron deficiency or vitamin deficiency.
- Moderately high RDW (16–18%) → often linked to anaemia, chronic illness, or inflammation.
- Severely high RDW (above 18%) → could point to serious issues such as advanced anaemia, bone marrow disorders, or cardiovascular risk.
In short, a RDW above 18% is generally considered potentially What Level of RDW Is Dangerous and should prompt medical investigation. However, the interpretation always depends on other blood parameters like haemoglobin, MCV (mean corpuscular volume), and overall clinical symptoms.
Why High RDW Can Be a Warning Sign
A high What Level of RDW Is Dangerous indicates a big difference in the size of red blood cells, which often suggests an underlying imbalance in production. Some potential causes include:
- Iron deficiency anaemia
- Vitamin B12 or folate deficiency
- Liver disease
- Bone marrow disorders
- Chronic inflammation or infection
- Cardiovascular disease risk
Studies show that a high RDW has even been linked to higher mortality risk in older adults, making it a useful marker beyond anaemia alone.
Symptoms That May Appear With High RDW
A slightly elevated RDW on its own might not cause symptoms. But if the underlying issue progresses, you may notice:
- Fatigue and weakness
- Pale or yellowish skin
- Shortness of breath
- Dizziness or fainting
- Heart palpitations
- Cold hands and feet
If you have any of these symptoms alongside an abnormal RDW result, it’s wise to seek medical advice promptly.
Can Low RDW Be Dangerous Too?
While high RDW is more commonly associated with health risks, low RDW values (below 11%) are less common but can still raise concerns. A very low RDW may suggest:
- A rare bone marrow disorder
- Certain chronic illnesses
- Technical errors in blood testing
Low RDW is generally not as clinically significant as high RDW, but persistent abnormalities should always be reviewed by a doctor.
RDW and Anaemia: The Strongest Connection
Anaemia is the most common condition linked to abnormal RDW. By looking at What Level of RDW Is Dangerous together with MCV (the average size of red blood cells), doctors can determine the likely type of anaemia:
- High RDW + Low MCV → Iron deficiency anaemia.
- High RDW + High MCV → Vitamin B12 or folate deficiency.
- Normal RDW + Low MCV → Thalassemia trait (genetic).
This pairing helps pinpoint treatment quickly and accurately.
When to Seek Medical Help
You should consult your GP or a haematologist if your blood test shows:
- RDW above 16–18%, especially with symptoms.
- RDW persistently outside the normal range.
- Abnormal RDW combined with low haemoglobin.
- Any signs of unexplained fatigue, weakness, or breathlessness.
In some cases, further tests such as iron studies, vitamin levels, or bone marrow biopsies may be required.
How to Improve Abnormal RDW Levels
Improving your What Level of RDW Is Dangerous depends on treating the underlying cause. Common strategies include:
- Iron supplements for iron deficiency.
- Vitamin B12 or folate supplementation.
- Dietary adjustments: leafy greens, red meat, legumes, fortified cereals.
- Managing chronic conditions like kidney or liver disease.
- Regular exercise and healthy lifestyle to improve cardiovascular outcomes.
Myths and Misconceptions About RDW
Many people panic after seeing an abnormal What Level of RDW Is Dangerous result, but here are a few myths to clear up:
- “A high RDW always means cancer.”
False — while bone marrow disorders can raise RDW, most cases are due to nutritional deficiencies. - “Normal RDW means perfect health.”
Not necessarily — you can still have anaemia or other issues with normal RDW if other blood values are off. - “RDW doesn’t matter.”
Wrong — RDW has been proven in research to predict cardiovascular risk and mortality.
FAQs About RDW
What level of RDW is considered critical?
An RDW above 18% is often considered critical and should be investigated immediately.
Can dehydration affect RDW?
Mildly, yes. Severe dehydration may cause temporary changes in red blood cell volume.
Does high RDW always mean anaemia?
No. RDW can be high due to vitamin deficiencies, liver disease, or inflammation without anaemia.
Is RDW a reliable predictor of heart disease?
Research suggests high RDW is linked to increased cardiovascular risk, but it must be interpreted with other factors.
Can diet improve RDW naturally?
Yes. A diet rich in iron, folate, and vitamin B12 can improve red blood cell health and reduce abnormal RDW.
Conclusion
So, what level of RDW is dangerous? Generally, values above 18% raise red flags and should never be ignored. While RDW alone cannot diagnose a condition, it’s a powerful indicator when paired with other blood results. High RDW often points to anaemia, nutritional deficiencies, or chronic disease, and in some cases it may predict cardiovascular risk.
If your RDW is abnormal, don’t panic — but do follow up with your GP. With proper diagnosis and treatment, RDW levels can usually be corrected.
