Red Blood Cell Count
Also written as: RBC, erythrocyte count
The number of red blood cells in a set volume of blood - the cells that carry oxygen.
What it measures
The number of red blood cells in a fixed volume of blood, counted by an automated analyzer. Red blood cells carry oxygen from the lungs to the rest of the body using the protein hemoglobin.
Why a doctor orders it
It is a standard part of every complete blood count rather than a test ordered on its own. Clinicians review it alongside hemoglobin and hematocrit when considering anemia, blood loss, or an unusually high red cell count.
What is generally associated with a higher result
Broadly associated with dehydration, which concentrates the blood, and with smoking, living at high altitude, and lung or heart conditions that reduce oxygen levels. Less commonly it reflects conditions in which the bone marrow makes extra red cells.
What is generally associated with a lower result
Broadly associated with the many forms of anemia, including blood loss, low iron or vitamin stores, and chronic illness. It also runs lower in pregnancy, when extra fluid in the blood dilutes the cells without anything being wrong.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Hydration on the day of the draw - dehydration raises it, lots of fluids lower it
- Pregnancy, which dilutes the blood normally
- Recent blood donation
- Smoking and living at altitude
- How long the tourniquet was on during the draw
Questions to take to your appointment
- Are my hemoglobin and hematocrit telling the same story as this count?
- Could my hydration on the day of the draw have shifted this?
- Do the red cell size measurements on the same panel point to a particular pattern?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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