CBC Blood Test: Complete Blood Count Results Explained

RDW-CV Normal Range: High, Low & What Your Blood Test Result Means

Sample type: Whole Blood

Other names: RDW-CV, RDW CV, RDW-CV Blood Test, RDW-CV Low, RDW-CV High, RDW-CV Normal Range, RDW, RDW %, RDW Blood Test, Red Cell Distribution Width, Red Cell Distribution Width CV, Red Cell Distribution Width Coefficient of Variation, RBC Distribution Width, RBC Distribution Width CV, RBC Distrib Width, RED DISTRIB. WIDTH, RDW Coefficient of Variation, RDW-CV Low Meaning, RDW-CV Blood Test Low, RDW-CV Blood Test High, RDW-CV Normal Range Female, RDW-CV Normal Range Male, What Is RDW In Blood Test, RDW Blood Test Low, RDW Blood Test High, Low RDW Blood Test, RDW Standard Deviation (see also RDW-SD page), Erythrocyte Distribution Width, Red Blood Cell Distribution Width, RDW-CD, RDW Low, RDW High, RDW Low Blood Test, RDW Normal Range, RDW Low Meaning, RDW High Meaning, RDW-CV Bajo (Spanish), RDW-CV Alto (Spanish), RDW-SD (fL version — see dedicated page)

Optimal result: 11.7 – 15.4 %

Labcorp

Written May 19, 2026

Updated May 19, 2026

By Healthmatters Editorial Team

Peer-reviewed sources

A high RDW-CV means your red blood cells vary more in size than expected — a condition called anisocytosis. This is one of the most common mild abnormalities found on a CBC and is usually caused by a nutritional deficiency rather than a serious disease.

Most common causes: Iron deficiency (most common), vitamin B12 deficiency, folate deficiency, mixed deficiencies, recent blood loss, chronic inflammation, liver disease, and recovery from illness.

Mild elevation (14.5–17%) with normal haemoglobin: Very common. Often represents early iron or B12/folate deficiency before anaemia develops. Doctors typically order iron studies and B12/folate levels as a next step. No urgent action is usually required.

Moderate to marked elevation (above 17–20%) with other CBC abnormalities warrants clinical evaluation to identify the underlying cause and guide treatment.

High RDW-CV is not dangerous by itself. It becomes clinically significant when combined with a drop in haemoglobin, abnormal MCV, or symptoms of anaemia.

A low RDW-CV means your red blood cells are very uniform in size. In most cases this is a normal finding and does not require treatment.

Low RDW-CV is clinically significant only when it accompanies other CBC abnormalities. The combination of low RDW-CV, low MCV, and low haemoglobin may suggest thalassaemia trait or iron deficiency anaemia — both of which warrant further evaluation with iron studies.

If your RDW-CV is low but haemoglobin, MCV, and other CBC markers are all normal, this is not a cause for concern and does not require follow-up in most cases.

RDW-CV (Red Cell Distribution Width – Coefficient of Variation) measures how much your red blood cells vary in size, expressed as a percentage. The normal range is approximately 11.5–14.5%. A high RDW-CV indicates anisocytosis — greater variation in cell size — most commonly from iron, B12, or folate deficiency. A low RDW-CV means cells are unusually uniform and is usually not clinically significant. RDW-CV is always interpreted alongside MCV and haemoglobin, not in isolation.

If your result is in fL (femtoliters) rather than %, it is RDW-SD — see our dedicated RDW-SD page.

QUICK ANSWER

RDW-CV measures how much your red blood cells vary in size, as a percentage. A mildly abnormal RDW-CV is extremely common and usually does not indicate anything serious by itself. Most people with a slightly high or low RDW-CV do not require urgent treatment.

RDW-CV is always interpreted alongside MCV and haemoglobin — never in isolation.

⚠️ Is your result in fL (femtoliters) rather than %? If your lab report shows a value like 42 fL, 47 fL, or 38 fL — that is RDW-SD, not RDW-CV. RDW-SD and RDW-CV are different measurements with different units and different reference ranges. → See our dedicated RDW-SD page for fL results

MOST COMMON RESULTS AT A GLANCE

Your RDW-CV	What it usually means
< 11.5%	Low — usually not clinically significant
11.5–14.5%	Normal
14.5–16%	Mildly elevated — common; correlate with haemoglobin and MCV
16–20%	Moderately elevated — evaluate with iron, B12, and folate
> 20%	Significant variation — clinical evaluation appropriate

Values just above or below the reference range are extremely common and often reflect normal biological variation. RDW-CV is never interpreted in isolation.

Normal reference range: approximately 11.5–14.5% (Some labs use 11.7–15.4% or 11.5–15.0% — always use the range on your specific lab report)

Result (%)	Interpretation
< 11.5%	Low — uniformly small or large cells; usually not clinically significant
11.5–14.5%	Normal
14.6–16%	Mildly elevated — correlate with MCV and haemoglobin
16–20%	Moderately elevated — evaluate for nutritional deficiency or chronic disease
> 20%	Higher elevation — medical evaluation appropriate

Reference ranges vary by laboratory. Always compare your result to the range on your specific report.

WHAT IS RDW-CV? (AND HOW IT DIFFERS FROM RDW-SD)

RDW-CV is the most commonly reported form of RDW in the United States (used by LabCorp and Quest as the default CBC measurement). It expresses red cell size variation as a percentage of the average cell size (MCV).

The two forms of RDW:

	RDW-CV	RDW-SD
Units	% (percentage)	fL (femtoliters)
What it measures	Size variation relative to average cell size	Actual width of the red cell size distribution curve
Influenced by MCV	Yes — elevated MCV can raise RDW-CV artificially	No — more independent
Normal range	~11.5–14.5%	~37–54 fL
More commonly reported	Yes — US labs (LabCorp, Quest)	International and hospital labs

Simple rule: if your result shows %, it is RDW-CV. If it shows fL, it is RDW-SD.

If your report shows fL, visit our RDW-SD page for the correct reference ranges and interpretation.

WHAT DOES HIGH RDW-CV MEAN?

A high RDW-CV indicates anisocytosis — your red blood cells are varying more in size than expected. Most mildly elevated RDW-CV results are caused by common and treatable nutritional deficiencies — not serious blood disorders.

Most common causes:

Iron deficiency (most common)
Vitamin B12 deficiency
Folate deficiency
Mixed nutritional deficiency (iron + B12, or iron + folate)
Recent blood loss or transfusion
Recovery phase after anaemia treatment — new reticulocytes temporarily increase variation
Chronic disease or inflammation
Liver disease

RDW-CV often changes before anaemia develops. In early iron, B12, or folate deficiency, haemoglobin may still be completely normal while RDW-CV is already elevated — because red cell size variation develops before haemoglobin concentration drops. This makes RDW-CV one of the most sensitive early signals of nutritional deficiency. A mildly elevated RDW-CV with normal haemoglobin is very common, treatable, and not an emergency.

High RDW-CV with normal haemoglobin: Very common. Usually represents early nutritional deficiency. Doctors frequently monitor this pattern or order iron, B12, and folate testing as a next step before initiating treatment.

WHAT DOES LOW RDW-CV MEAN?

A low RDW-CV means red blood cells are very uniform in size. Low RDW-CV by itself is rarely clinically important. In most cases, it is a normal finding and does not require treatment.

Low RDW-CV may appear when:

Red blood cells are consistently small (microcytic) — as in thalassaemia trait or early iron deficiency
Red blood cells are consistently large (macrocytic)
Bone marrow production is stable and uniform
Other CBC markers are normal

Is low RDW-CV dangerous? Usually no. Low RDW-CV without other CBC abnormalities or symptoms does not require treatment. If low RDW-CV accompanies low MCV and low haemoglobin, the combination warrants evaluation for thalassaemia trait or iron deficiency. Thalassaemia trait is a common genetic carrier state — most carriers live completely normal lives.

RDW-CV AND MCV PATTERNS

Interpreting RDW-CV alongside MCV is the standard approach to anaemia classification:

RDW-CV	MCV	Most likely cause
High	Low (< 80 fL)	Iron deficiency anaemia
High	Normal (80–100 fL)	Early/mixed deficiency, chronic disease
High	High (> 100 fL)	B12 or folate deficiency
Normal/Low	Low	Thalassaemia minor, anaemia of chronic disease
Normal	Normal	Normal CBC

WHAT LEVEL OF RDW-CV IS DANGEROUS?

No single RDW-CV percentage is inherently dangerous. Clinical significance depends on context.

RDW-CV becomes more concerning when:

High RDW-CV accompanies low haemoglobin
High RDW-CV accompanies abnormal MCV
Symptoms of anaemia are present (fatigue, pallor, shortness of breath, dizziness)
The elevation is persistent on repeat testing

Reassurance: Most mildly elevated RDW-CV results reflect common nutritional deficiencies — iron, B12, or folate — which are treatable. A single mildly elevated RDW-CV in an otherwise normal CBC with no symptoms is very common and rarely urgent.

When to see a doctor about an abnormal RDW-CV:

RDW-CV persistently elevated above 16% on repeat testing
Elevated RDW-CV alongside low haemoglobin or abnormal MCV
Fatigue, weakness, shortness of breath, dizziness, or pale skin
RDW-CV worsening over successive tests
Any CBC abnormality alongside the elevated RDW-CV

COMMON PHRASES SEEN ON LAB REPORTS

RDW-CV / RDW CV
RDW-CV BLOOD TEST
RDW / RDW %
RDW BLOOD TEST
RED CELL DISTRIBUTION WIDTH
RED CELL DISTRIBUTION WIDTH CV
RBC DISTRIBUTION WIDTH / RBC DISTRIB WIDTH
RED DISTRIB. WIDTH
RDW COEFFICIENT OF VARIATION
ERYTHROCYTE DISTRIBUTION WIDTH
RDW LOW / RDW HIGH
RDW-CV LOW / RDW-CV HIGH
RDW BLOOD TEST LOW / RDW BLOOD TEST HIGH
LOW RDW BLOOD TEST
RDW-CV BAJO / RDW-CV ALTO (Spanish)

Organize and understand all your lab results

Start organizing — $15/mo →

For Health Professionals Healthmatters Pro Multiple clients’ results in one dashboard. See Pro plans →

RDW-CV (Red Cell Distribution Width) in %

Every lab result you’ve ever had, charted and explained.

Healthmatters is a tracker for your lab results. Upload a report from any lab, any country — every marker charted and explained.

Start with my report →

Frequently Asked Questions

What does RDW-CV mean in a blood test?

RDW-CV (Red Cell Distribution Width – Coefficient of Variation) measures how much your red blood cells vary in size, expressed as a percentage. A normal RDW-CV is approximately 11.5–14.5%. High RDW-CV means more size variation (anisocytosis), most commonly from iron, B12, or folate deficiency. Low RDW-CV means cells are more uniform and is usually not clinically significant. Always interpreted alongside MCV and haemoglobin.

What is the normal range for RDW-CV?

The normal range is approximately 11.5–14.5%, though some labs use 11.7–15.4% or 11.5–15.0%. Values just above or below this range are common and not always clinically meaningful. Always use the reference range on your specific lab report.

What does high RDW-CV mean?

High RDW-CV means your red blood cells vary significantly in size (anisocytosis). The most common causes are iron deficiency, vitamin B12 deficiency, and folate deficiency. It often rises before haemoglobin drops, providing an early signal. Mild elevation with normal haemoglobin is common and usually prompts iron and B12/folate testing rather than immediate treatment.

What does low RDW-CV mean?

Low RDW-CV means red blood cells are more uniform in size than expected. This is usually not clinically significant. If accompanied by low MCV and low haemoglobin, it may indicate thalassaemia trait or iron deficiency — warranting further evaluation. Low RDW-CV alone with a normal CBC typically requires no action.

What does low RDW blood test mean?

A low RDW on a blood test means red blood cells are very uniform in size. In most cases this is not a health problem. If the rest of the CBC is normal — haemoglobin, MCV, and other markers — a low RDW typically requires no follow-up. It becomes more clinically relevant when accompanied by a low MCV or low haemoglobin.

What level of RDW-CV is dangerous?

No single percentage is inherently dangerous. RDW-CV becomes clinically concerning when it is persistently elevated alongside low haemoglobin, abnormal MCV, or symptoms of anaemia (fatigue, shortness of breath, dizziness). Mildly elevated RDW-CV with a normal CBC and no symptoms is very common and rarely requires urgent action.

What is the difference between RDW-CV and RDW-SD?

RDW-CV is expressed as a percentage and reflects size variation relative to average cell size (MCV). RDW-SD is expressed in femtoliters (fL) and reflects the actual spread of red cell sizes. If your result shows %, it is RDW-CV; if it shows fL, it is RDW-SD. RDW-CV is the standard form reported by US labs (LabCorp, Quest). For fL results, see our RDW-SD page.

What does RDW-CV low mean?

RDW-CV low means your red blood cells are very similar in size — more uniform than the reference range suggests is typical. This is usually a benign finding. It may be seen in thalassaemia trait or early iron deficiency where all cells are uniformly small. If haemoglobin and MCV are normal, low RDW-CV alone is not clinically actionable.

Can iron deficiency cause high RDW-CV with normal haemoglobin?

Yes — iron deficiency can raise RDW-CV before haemoglobin drops. The earliest effect of iron depletion is on red cell size variation, not haemoglobin concentration. A mildly elevated RDW-CV with normal haemoglobin is one of the earliest laboratory signs of iron deficiency and commonly prompts iron studies as a next step.

What does RDW mean on a blood test?

RDW (Red Cell Distribution Width) measures variation in red blood cell size. It is reported in two forms: RDW-CV (as a percentage, normal ~11.5–14.5%) and RDW-SD (in femtoliters, normal ~37–54 fL). Both are part of the CBC. High RDW in either form suggests anisocytosis — uneven red cell sizes — most commonly from nutritional deficiency. Low RDW is usually not significant.

Can dehydration affect RDW-CV?

Dehydration itself does not directly change RDW-CV, but it can affect other CBC markers (haemoglobin may appear falsely elevated, for example). A one-time mildly elevated RDW-CV measured during or after an illness — which often involves dehydration — is not clinically significant on its own.

Can stress affect RDW-CV?

Acute physiological stress (illness, surgery, infection) can transiently alter red blood cell production and cause a mildly elevated RDW-CV. Psychological stress alone does not directly change RDW-CV. A single mildly elevated value during or shortly after an illness is not a cause for concern.

Can alcohol raise RDW-CV?

Yes. Chronic or heavy alcohol use can raise RDW-CV through direct toxic effects on bone marrow and secondary folate deficiency (common with high alcohol intake). A mildly elevated RDW-CV in someone who drinks regularly often prompts a check of folate and MCV. This is reversible with reduced alcohol intake and nutritional correction.

Can pregnancy affect RDW-CV?

Pregnancy increases blood volume and iron requirements, which can cause iron deficiency. This commonly raises RDW-CV. Mild RDW-CV elevation in pregnancy is expected and typically managed with iron supplementation. Values normalise postpartum as iron stores recover.

Can RDW-CV return to normal?

Yes — RDW-CV normalises once the underlying cause is treated. However, it returns to normal slowly rather than quickly, because red blood cells live approximately 120 days. When iron, B12, or folate is replenished, new healthy red cells gradually replace the older abnormal ones over several weeks to months. This means RDW-CV may stay mildly elevated for 1–3 months even after treatment begins — this is expected and does not mean treatment is failing.

Clinical Sources & References

All our content is backed by peer-reviewed studies, academic research, and trusted medical sources. We’re committed to accuracy and transparency — see our editorial policy for details.

RDW as an Early Marker of Iron Deficiency

J Liaquat Uni Med Health Sci. 2018;17(03):165-9 · 2018 View source ↗
Clinical Significance of Red Cell Distribution Width

Kidney Res Clin Pract. 2016 Jun;35(2):114-8. doi: 10.1016/j.krcp.2016.03.003. Epub 2016 May 24. PMID: 27366667; PMCID: PMC4919502. · 2016 View source ↗
Beyond anemia: Red cell distribution width as a universal biomarker in contemporary medicine

Department of Medicine, Farukh Hussain Medical College, Agra, Uttar Pradesh, India. · 2025 View source ↗
Clinical and Laboratory Standards Institute (CLSI) Reference Ranges

CLSI. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory. · 2010 View source ↗
Improved classification of anemias by MCV and RDW

Am J Clin Pathol · 1983 View source ↗
Red blood cell distribution width: A simple parameter with multiple clinical applications

Crit Rev Clin Lab Sci · 2015 View source ↗
Complete Blood Count (CBC) With Differential, Reflex to Peripheral Smear Review

Labcorp · 2025 View source ↗

Article Review Log

Last reviewed May 19, 2026

Originally published May 19, 2026

Reviewed by HealthMatters Editorial Team

Written by Healthmatters Editorial Team

Organize and understand all your lab results

Start organizing — $15/mo →

For Health Professionals Healthmatters Pro Multiple clients’ results in one dashboard. See Pro plans →

Healthmatters Lifetime Plan

Pay $250. Track your health forever

One payment. No renewals. Yours for life.

10,000+ biomarkers explained · trends over time

See other plans →

Secure checkout via Stripe · GDPR & HIPAA

We accept results from any lab

LabCorp Quest Diagnostics Genova Diagnostics DUTCH Test Doctor's Data Vibrant America ZRT Laboratory Cyrex Labs + any other lab

What members are saying

★★★★★ 10,000+ happy members

★★★★★

"Watching my numbers move over the years — instead of forgetting last time's results — completely changed how I manage my health."

Daniel

Member since 2022

★★★★★

"Living across several countries made keeping my lab results organized a real challenge. Healthmatters brought my results from the USA, Spain, and Germany together — 20 years of history, with long-term trends instead of scattered reports."

Ben

Member since 2021 · tracks across countries

★★★★★

"Standard lab ranges are too wide for how I practice — 'normal' isn't optimal. I set my own bands, so a client sees yellow before a marker goes officially out of range. That's the conversation I want to be having."

Dr. Alexandra

Functional medicine · 6 yrs on Pro

RDW-CV Normal Range: High, Low & What Your Blood Test Result Means

QUICK ANSWER

MOST COMMON RESULTS AT A GLANCE

WHAT IS RDW-CV? (AND HOW IT DIFFERS FROM RDW-SD)

WHAT DOES HIGH RDW-CV MEAN?

WHAT DOES LOW RDW-CV MEAN?

RDW-CV AND MCV PATTERNS

WHAT LEVEL OF RDW-CV IS DANGEROUS?

COMMON PHRASES SEEN ON LAB REPORTS

Organize and understand all your lab results

Every lab result you’ve ever had, charted and explained.

Frequently Asked Questions

Related Biomarkers

Related Health Conditions

Pay $250. Track your health forever

What members are saying