RDW 18.6 %
- Below typical range
- Normal
- Borderline high
- High
- Very high
At a glance
- Your band
- High · 16–20 %
- Distance from typical range
- 4.1 % above 14.5
What 18.6 % means
An RDW of 18.6 % is clearly above the typical adult range of about 11.5–14.5%. This usually means your body is producing red cells of noticeably different sizes.
An RDW in this range most often points to a nutrient deficiency — iron, vitamin B12, or folate — that is disturbing red cell production, or to recovery after blood loss, when a wave of new, larger cells mixes with older ones. It can also reflect liver disease, ongoing red cell breakdown (hemolysis), or a recent blood transfusion, which literally mixes another person's cells with yours. The RDW itself does not identify which of these is happening; the rest of the CBC and follow-up tests do.
Most US labs consider an adult RDW-CV of roughly 11.5% to 14.5% normal (some labs extend the upper limit to about 15%, and MedlinePlus cites slightly different figures for men and women); this ladder follows the widely used 11.5–14.5% convention.
Common causes
- Iron deficiency anemia — the most common cause
- Vitamin B12 or folate deficiency
- Combined deficiencies (for example, iron plus B12), which can raise RDW while keeping MCV deceptively normal
- Recent significant blood loss, or active recovery from anemia (a surge of new young red cells)
- Recent blood transfusion
- Chronic liver disease or heavy alcohol use
- Hemolysis — red cells breaking down faster than normal
- Chronic kidney disease or ongoing inflammatory illness
Symptoms that can go with it
- Fatigue or low energy
- Shortness of breath with activity
- Pale skin, lips, or nail beds
- Dizziness or lightheadedness
- Rapid or pounding heartbeat
- Cold hands and feet
- Brittle nails or unusual cravings (such as ice) with iron deficiency
Sensible next steps
- Book a non-urgent appointment with your clinician to go over the full CBC — this level warrants an explanation but is not an emergency
- Expect follow-up tests such as ferritin (iron stores), vitamin B12, and folate, which usually identify the cause
- Tell your clinician about any blood loss: heavy periods, dark or bloody stools, recent surgery, or frequent blood donation
- Do not start iron pills on your own — taking iron without a confirmed deficiency can hide the real cause and cause harm
- Follow through on the repeat CBC your clinician schedules to confirm the value is improving with treatment
Frequently asked questions
Is 18.6 % a normal RDW level?
No — 18.6 % is above the typical adult range of about 11.5–14.5%. It most often points to low iron, vitamin B12, or folate, or to recovery from blood loss, and is worth reviewing with your clinician alongside your hemoglobin and MCV.
What does a high RDW mean?
At 18.6 %, there is a clear excess of size variation. The usual explanations are iron deficiency, B12 or folate deficiency, recovery from blood loss, or a recent transfusion. Your clinician will typically order ferritin, B12, and folate tests to pin down the cause.
Can RDW be high when hemoglobin is normal?
Yes. RDW often rises before hemoglobin falls, so a high RDW with normal hemoglobin can be an early warning that iron, vitamin B12, or folate stores are running low. It can also follow recent blood donation or blood loss that your body is already correcting. A simple set of follow-up tests — usually ferritin, B12, and folate — can check for a developing deficiency before it becomes anemia.
Is a low RDW something to worry about?
No. A low RDW simply means your red blood cells are very uniform in size, and no disease is diagnosed from a low RDW alone. If your hemoglobin, MCV, and the rest of your CBC are normal, a low RDW needs no follow-up beyond mentioning it at your next visit.
How can I lower a high RDW?
With 18.6 %, ask your clinician to identify the cause first — usually with ferritin, B12, and folate tests. Treating the confirmed deficiency (or the underlying condition) brings RDW down gradually over two to four months; there is no faster shortcut, and untargeted supplements can hide the real problem.
What is the difference between RDW-CV and RDW-SD?
Both measure the same thing — variation in red cell size — but on different scales. RDW-CV is a percentage (typical adult range about 11.5–14.5%) and is what most US labs report as 'RDW.' RDW-SD is reported in femtoliters (fL), with a typical range of roughly 39–46 fL, and is less affected by the average cell size. If your report shows a number in the 40s with 'fL' next to it, you are looking at RDW-SD, and percentage-based ranges do not apply to it.
Does a high RDW mean cancer?
Almost never. The overwhelming majority of high RDW results are explained by iron, B12, or folate deficiency, blood loss, or chronic illness — not cancer. Research has linked higher RDW to worse outcomes in various diseases, but that makes it a general, non-specific marker of illness and inflammation, not a cancer test. In older adults with a persistently high RDW and other unexplained CBC abnormalities, clinicians may check for bone marrow disorders, which is one reason follow-up matters — but a high RDW by itself is not a reason to fear cancer.
Check a different RDW value
Sources
- RDW (Red Cell Distribution Width) — MedlinePlus (National Library of Medicine)
- RDW Blood Test — Cleveland Clinic
- Complete Blood Count (CBC) — Mayo Clinic
- Complete Blood Count (CBC) — MedlinePlus (National Library of Medicine)
- Anemia (StatPearls) — NCBI Bookshelf
Educational information, not medical advice. Reference ranges vary between labs — always compare with the range printed on your own report and discuss results with your doctor. Full disclaimer