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RBC blood test

Red blood cell count

In short

A typical adult RBC result is 3.92 to 5.13 x10^6/µL for women and 4.35 to 5.65 x10^6/µL for men. A slightly high count most often comes from dehydration, smoking or living at high altitude. A high count of small cells can also come from a harmless inherited trait. Always read your result against the range printed on your own report.

The number of red blood cells, which carry oxygen around the body.

Red blood cells carry oxygen from the lungs to the rest of the body. Doctors rarely read this count alone. They read it with hemoglobin, the protein that carries the oxygen, and with MCV, the average cell size.

Is my RBC high or low?

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Typical range

ForRangeUnit
Female3.92–5.13x10^6/µL
Male4.35–5.65x10^6/µL

Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.

If your RBC is high

A slightly high count most often comes from dehydration, smoking or living at high altitude. A high count of small cells can also come from a harmless inherited trait.

Common reasons

  • Not drinking enough before the test (dehydration)
  • Smoking, which pushes the body to make more red cells
  • Living at high altitude
  • Thalassemia trait, a usually harmless inherited difference that makes many small cells
  • Sleep apnea (breathing pauses in sleep) or a long-term lung condition
  • Some hormone treatments, especially male hormone therapy
  • Less often: polycythemia vera, a bone marrow condition making too many red cells

If your RBC is low

A low count usually comes with low hemoglobin, which is called anemia. Anemia is common, and the size of the cells helps show the likely reason.

Common reasons

  • Low iron, often from heavy periods or pregnancy
  • Pregnancy, when extra fluid naturally thins the blood
  • Low vitamin B12 or folate
  • Long-term kidney disease or ongoing inflammation
  • Recent bleeding, surgery or blood donation
  • Less often: slow, hidden bleeding from the stomach or bowel
  • Less often: red cells breaking down early, or a bone marrow problem

What can throw it off

Dehydration, recent bleeding, pregnancy and living at high altitude can all shift the count.

Questions to take to your appointment

  1. 1Do my hemoglobin and hematocrit point the same way?
  2. 2Should my iron, vitamin B12 or folate be checked?
  3. 3Is this small enough to just repeat the test?

Read together with

Doctors rarely read RBC alone. These usually sit next to it.

Quick answers

What is the RBC blood test?

RBC (Red blood cell count): The number of red blood cells, which carry oxygen around the body. Red blood cells carry oxygen from the lungs to the rest of the body. Doctors rarely read this count alone. They read it with hemoglobin, the protein that carries the oxygen, and with MCV, the average cell size.

What is a normal RBC level?

For most adults, RBC is typically 3.92 to 5.13 x10^6/µL for women and 4.35 to 5.65 x10^6/µL for men. Labs differ a little, so the range printed next to your result is the one to go by.

What does a high RBC mean?

A slightly high count most often comes from dehydration, smoking or living at high altitude. A high count of small cells can also come from a harmless inherited trait. Common reasons include not drinking enough before the test (dehydration); smoking, which pushes the body to make more red cells; living at high altitude; and thalassemia trait, a usually harmless inherited difference that makes many small cells. A doctor reads it together with your other results and how you feel.

What does a low RBC mean?

A low count usually comes with low hemoglobin, which is called anemia. Anemia is common, and the size of the cells helps show the likely reason. Common reasons include low iron, often from heavy periods or pregnancy; pregnancy, when extra fluid naturally thins the blood; low vitamin B12 or folate; and long-term kidney disease or ongoing inflammation.

What can affect my RBC result?

Dehydration, recent bleeding, pregnancy and living at high altitude can all shift the count.

What should I ask my doctor about my RBC?

Questions worth taking to the appointment: Do my hemoglobin and hematocrit point the same way? Should my iron, vitamin B12 or folate be checked? Is this small enough to just repeat the test?

What this page can’t do

It reads each number on its own.

Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.

It doesn't know you.

Your age, your medicines, how you feel and your last result all change what a number means.

It doesn't remember.

Close this page and your results are gone. That's on purpose: nothing was ever sent to us.

We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.

Vita: Health Coach on the App Store

Sources

Stuck on a word? See the medical words. How we choose our sources. More about Vita Health Coach.