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RBC indices
Definition
Red blood cell (RBC) indices are part of the complete blood count (CBC) test. They are used to help diagnose the cause of anemia, a condition in which there are too few red blood cells.
The indices include:
- Average red blood cell size (MCV)
- Hemoglobin amount per red blood cell (MCH)
- The amount of hemoglobin relative to the size of the cell (hemoglobin concentration) per red blood cell (MCHC)
See also: RBC count
Alternative Names
Erythrocyte indices; Blood indices; Mean corpuscular hemoglobin (MCH); Mean corpuscular hemoglobin concentration (MCHC); Mean corpuscular volume (MCV); Red blood cell indices
How the Test is Performed
A blood sample is needed. For information on how this is done, see: Venipuncture
The values for MCHC, and MCH are calculated from the hemoglobin (Hgb), hematocrit (Hct), and RBC count:
- MCHC = Hgb/Hct
- MCH = Hgb/RBC count
The MCV is measured directly by a machine.
How to Prepare for the Test
No special preparation is necessary.
How the Test Will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
RBCs transport hemoglobin which, in turn, transports oxygen. The amount of oxygen tissues receive depends on the amount and function of RBCs and hemoglobin.
The MCV reflects the size of red blood cells. The MCH and MCHC reflect the hemoglobin content of red blood cells. These RBC measures are used to diagnose types of anemia.
Anemias are defined based on cell size (MCV) and amount of Hgb (MCH).
- MCV less than lower limit of normal: microcytic anemia
- MCV within normal range: normocytic anemia
- MCV greater than upper limit of normal: macrocytic anemia
- MCH less than lower limit of normal: hypochromic anemia
- MCH within normal range: normochromic anemia
- MCH greater than upper limit of normal: hyperchromic anemia
Normal Results
- MCV: 80 - 100 femtoliter
- MCH: 27 - 31 picograms/cell
- MCHC: 32 - 36 grams/deciliter
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 samples.
What Abnormal Results Mean
This test is used to diagnose the cause of anemia. The following are the types of anemia and their causes:
- Normocytic/normochromic (NC/NC) anemia is caused by sudden blood loss, prosthetic heart valves, sepsis, tumor, long-term disease or aplastic anemia.
- Microcytic/hypochromic anemia is caused by iron deficiency, lead poisoning, or thalassemia.
- Microcytic/normochromic anemia results from a deficiency of the hormone erythropoietin from kidney failure.
- Macrocytic/normochromic anemia results from chemotherapy, folate deficiency, or vitamin B-12 deficiency.
Risks
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample 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)
References
Bunn HF. Approach to the anemias. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 161.Reviewed By: Todd Gersten, MD, Hematology/Oncology, Palm Beach Cancer Institute, West Palm Beach, FL. Review provided by VeriMed Healthcare Network. Also reviewed by Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington; David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.
