Skip to content

Maximum Diameter of Blood Red Blood Cells (RBCs) in Serum/Plasma

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

This test measures the largest diameter of red blood cells (RBCs) in your blood sample. It helps assess overall RBC size distribution, which can be important for diagnosing conditions affecting red blood cells.

Quick summary

["This test helps doctors evaluate red blood cell health and identify potential blood disorders."]

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

Key facts at a glance

LOINC
111891-8
Short code
Max diameter Blry tr Endscpy
Synonyms
Max 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

What Does This Test Measure?

The test specifically looks at the largest red blood cell diameter in your blood, often used alongside other RBC measurements like mean corpuscular volume (MCV). This can help determine if RBCs are consistently small (microcytic), large (macrocytic), or of normal size (normocytic).

Why Might You Need This Test?

Doctors may order this test if they suspect conditions like anemia, blood disorders, or other health issues that affect RBC size. It can also be part of a broader evaluation when symptoms such as fatigue, pale skin, or unusual bleeding occur.

Sample and Testing Process

A blood sample is drawn, and the serum or plasma is analyzed to measure the largest RBC diameter. This is typically done using automated blood cell analyzers that calculate RBC dimensions.

Common Conditions Monitored

While maximum RBC diameter alone isn’t always definitive, it’s often used in conjunction with other tests to diagnose or monitor conditions such as pernicious anemia, thalassemia, or other inherited blood disorders that can cause RBCs to vary in size.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

RBC Size Measurement

Frequently asked questions

Why was this test ordered?
Your doctor may have ordered this test to investigate symptoms like fatigue, pale skin, unusual bruising, or unexplained anemia. It can also be part of routine blood work or monitoring for conditions affecting red blood cells.
How does this test differ from other RBC tests?
Unlike tests that measure average RBC size (like MCV), this test specifically looks at the largest RBC in your sample. It’s often used alongside other RBC measurements to get a fuller picture of your blood health.
What do my results mean?
Results are usually compared to your baseline or other relevant tests. If your largest RBC diameter is unusually large or small, it may indicate a blood disorder. Your doctor will discuss the results in the context of your symptoms and other test findings.
  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