An RBC count is a blood test that tells how many red blood cells (RBCs) you have.
RBCs contain hemoglobin, which carries oxygen. How much oxygen your body tissues get depends on how many RBCs you have and how well they work.
Erythrocyte count; Red blood cell count
How the test is performed
A blood sample is needed. For information on how this is done, see: Venipuncture
How to prepare for the test
No special preparation is necessary for adults.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
The RBC count is almost always part of the CBC (complete blood count) test.
The test can help diagnose anemia and other conditions affecting red blood cells.
Additional conditions under which an RBC count may be performed:
- Alport syndrome
- Drug-induced immune hemolytic anemia
- Hemolytic anemia due to G6PD deficiency
- Hereditary anemias, such as thalassemia
- Idiopathic autoimmune hemolytic anemia
- Immune hemolytic anemia
- Macroglobulinemia of Waldenstrom
- Paroxysmal nocturnal hemoglobinuria (PNH)
- Primary myelofibrosis
The general the range is as follows:
- Male: 4.7 to 6.1 million cells per microliter (cells/mcL)
- Female: 4.2 to 5.4 million cells/mcL
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What abnormal results mean
Higher-than-normal numbers of RBCs may be due to:
- Cigarette smoking
- Congenital heart disease
- Cor pulmonale
- Dehydration (such as from severe diarrhea)
- Kidney tumor (renal cell carcinoma)
- Low blood oxygen levels (hypoxia)
- Pulmonary fibrosis
- Polycythemia vera
Your RBC count will increase for several weeks when you move to a higher altitude.
Drugs that can increase the RBC count include:
Lower-than-normal numbers of RBCs may be due to:
- Bone marrow failure (for example, from radiation, toxins, or tumor)
- Erythropoietin deficiency (secondary to kidney disease)
- Hemolysis (RBC destruction) due to transfusion, blood vessel injury, or other cause
- Hemorrhage (bleeding)
- Multiple myeloma
- Nutritional deficiencies of:
- Vitamin B-12
- Vitamin B-6
Drugs that can decrease the RBC count include:
- Chemotherapy drugs
What the risks are
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Bunn HF. Approach to the anemias. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 161.