Understanding the RDW Blood Test

Red cell distribution width (RDW) is a measure included in a standard complete blood count (CBC). It reflects the variation in size of your red blood cells. A higher RDW indicates more variation—and can point to underlying health issues.

Key points about RDW:

• Normal RDW range: roughly 11.5 %–14.5 % (may vary slightly by lab)
• High RDW means red blood cells differ more in size than usual
• Often used alongside other CBC values (hemoglobin, MCV) to help diagnose anemia

Common Causes of High RDW

An elevated RDW alone doesn’t diagnose a specific disease. Instead, it serves as a clue that prompts further investigation. Common non-serious causes include:

• Nutrient deficiencies
  • Iron, vitamin B12 or folate deficiency
• Recent blood loss or hemolysis
• Recovery from anemia (new cells differ in size)
• Chronic inflammation or infection

High RDW and Heart Disease

What the research shows

Several large observational studies (for example, published in journals like Circulation and endorsed by the American Heart Association) have found that elevated RDW correlates with a higher risk of:

• Heart failure
• Coronary artery disease
• Increased mortality after a heart attack

Possible explanations

• Inflammation: Chronic inflammation can impair red blood cell maturation, raising RDW.
• Oxidative stress: Damages red blood cells, increasing size variation.
• Nutrient deficiency: Common in heart disease; poor iron or B12 status affects both heart health and RDW.

What it means for you

• A high RDW by itself does not confirm heart disease.
• It’s one piece of the puzzle—doctors consider it along with symptoms (chest pain, shortness of breath), risk factors (high blood pressure, smoking), imaging and other blood tests (troponin, cholesterol).
• If you have cardiovascular risk factors, a high RDW may prompt closer monitoring and lifestyle optimization.

High RDW and Cancer

Observational links

Researchers have noted that some cancers are associated with elevated RDW:

• Solid tumors (lung, colon)
• Hematologic malignancies (leukemia, lymphoma)

Some studies suggest high RDW may predict poorer outcomes, possibly because cancer-related inflammation alters red cell production.

Important caveats

• Not diagnostic: A high RDW is not a cancer test.
• Non-specific: Many benign conditions raise RDW more commonly than cancer.
• Context matters: Weight loss, unexplained fatigue, night sweats or abnormal imaging would raise suspicion—RDW alone won’t.

How Your Doctor Interprets High RDW

When your RDW blood test comes back high, your clinician will:

1. Review symptoms
   • Fatigue, dizziness, bleeding, chest discomfort
2. Examine other CBC values
   • Mean corpuscular volume (MCV)
   • Hemoglobin and hematocrit
3. Order additional tests as needed
   • Iron studies, vitamin B12/folate levels
   • Inflammatory markers (CRP, ESR)
   • Cardiac biomarkers or imaging
   • Cancer screening tests when indicated
4. Consider your medical history
   • Chronic diseases (kidney, liver, autoimmune)
   • Family history of anemia, heart disease, cancer
5. Plan further evaluation or treatment
   • Dietary changes, supplements for deficiencies
   • Adjustments to heart medications or anticoagulants
   • Referrals to specialists if a serious condition is suspected

When to Seek Medical Attention

Even though a slightly elevated RDW often has a benign cause, you should speak to a doctor if you experience:

• Chest pain, palpitations or shortness of breath
• Unexplained weight loss or night sweats
• Persistent fatigue or dizziness
• Unusual bleeding or bruising

If any symptom feels severe or life threatening, seek emergency care immediately.

Tools to Help You Decide

Not sure whether your symptoms warrant an in-person visit? Try a free, online symptom check, using the doctor approved Ubie Symptom Checker. It can help you understand possible causes and next steps, and guide you on when to see a healthcare professional.

Take-Home Messages

• A high RDW on your CBC is a warning sign, not a diagnosis.
• It can be elevated due to:
  • Nutrient deficiencies
  • Chronic inflammation or infection
  • Recent blood loss or recovery from anemia
  • Rarely, bone marrow disorders, cancer or heart disease
• In heart disease, high RDW often reflects inflammation and worse outcomes, but it’s only one factor.
• In cancer, high RDW correlates with prognosis but is not a screening tool.
• Always interpret RDW in the context of symptoms, other lab values and medical history.
• Follow up with your doctor for a thorough evaluation.

Speak to a doctor about any serious or life-threatening concerns. Your healthcare provider can interpret your RDW blood test in full context and recommend appropriate next steps.