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Middle Diameter of Red Blood Cells (RBC) Measurement

Published: August 9, 2026Updated: August 16, 2026

This test measures the average width of red blood cells (RBCs) to help assess their size distribution, which can be useful in diagnosing certain blood disorders.

Quick summary

["Your RBCs’ size distribution may signal conditions like anemia or blood disorders."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
111893-4
Short code
Mid diameter Blry tr Endscpy
Synonyms
Mid diameter Blry tr Endscpy
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
endoscopy
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Matters in Diagnosis

Red blood cells vary slightly in size, and measuring their average width helps identify if they’re consistently too large (macrocytic) or too small (microcytic), which can point to underlying health issues like vitamin deficiencies, genetic disorders, or other conditions.

What to Expect Before the Test

No special preparation is needed. You’ll likely have a simple blood draw from a vein in your arm, similar to other routine blood tests.

Common Conditions This Test Helps Detect

This test may be part of a broader evaluation for conditions like pernicious anemia, vitamin B12 deficiency, or other blood-related disorders where RBC size abnormalities are common.

How Results Are Interpreted

Results are compared to general reference ranges for RBC width, though individual labs may use slightly different standards. Your healthcare provider will discuss any deviations in context with your overall health.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

RBC Mean Width

Frequently asked questions

What might cause abnormal RBC width?
Changes in RBC width can occur due to genetic factors, chronic illnesses, medications, or nutritional deficiencies. For example, very large RBCs may suggest folate or B12 deficiency, while very small RBCs could indicate iron deficiency or other blood disorders.
How often is this test ordered?
This test is often included as part of a complete blood count (CBC) or when evaluating symptoms like fatigue, weakness, or unusual bleeding. Your doctor may order it periodically if you have a known condition affecting RBCs.
Can lifestyle changes affect RBC width?
Yes, diet (e.g., iron, folate, or B12-rich foods), hydration, and certain medications can influence RBC size. Discuss any changes in your diet or supplements with your healthcare provider if you’re concerned about your test results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy