MedlinePlus Medical Encyclopedia: RBC indices

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RBC indices

Contents of this page:
Alternative names Definition How the test is performed How to prepare for the test How the test will feel	Why the test is performed Normal Values What abnormal results mean What the risks are Special considerations

Alternative names

Erythrocyte indices; Blood indices; Red cell mass measurement; MCH (mean corpuscular hemoglobin); MCHC (mean corpuscular hemoglobin concentration); MCV (mean corpuscular volume)

Definition Return to top

Red blood cell (RBC) indices are part of the complete blood count (CBC) test. The indices include:

Average red blood cell size (MCV)
Hemoglobin amount per red blood cell (MCH)
Hemoglobin concentration (hemoglobin amount relative to the size of the cell) per red blood cell (MCHC)

Red blood cells transport hemoglobin which, in turn, transports oxygen. The amount of oxygen received by tissue depends on the amount and function of RBCs and hemoglobin. The MCV, MCH, and MCHC reflect the size and hemoglobin content of individual red blood cells.

See also RBC count.

How the test is performed Return to top

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to swell with blood.

A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

The values for MCHC, and MCH are derived from the hemoglobin (Hgb), hematocrit (Hct), and red blood cell count (RBC) by mathematical calculations:

MCHC = Hgb/Hct
MCH = Hgb/RBC

The MCV is measured directly.

How to prepare for the test Return to top

No special preparation is necessary.

For infants and children, the preparation you can provide for this test depends on your child's age and previous experience. For general information regarding how you can prepare your child, see the following topics:

infant test or procedure preparation (birth to 1 year)
toddler test or procedure preparation (1 to 3 years)
preschooler test or procedure preparation (3 to 6 years)
schoolage test or procedure preparation (6 to 12 years)
adolescent test or procedure preparation (12 to 18 years)

How the test will feel Return to top

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 Return to top

MCV values reflect the size, and MCH and MCHC reflect the hemoglobin concentration of individual cells. These RBC indices are useful in the diagnosis of types of anemia.

Anemias are classified on the basis of cell size (MCV) and amount of Hgb (MCH).

MCV less than lower limit of normal: microcytic
MCV within normal range: normocytic
MCV greater than upper limit of normal: macrocytic
MCH less than lower limit of normal: hypochromic
MCH within normal range: normochromic
MCH greater than upper limit of normal: hyperchromic

Normal Values Return to top

MCV: 80 to 100 femtoliter
MCH: 27 to 31 picograms/cell
MCHC: 32 to 36 grams/deciliter

What abnormal results mean Return to top

Anemias have been classified as follows:

Normocytic/normochromic (NC/NC) anemia -- from blood loss, prosthetic heart valves, Sepsis, tumor, or aplastic anemia (for example, due to chloramphenicol toxicity)
Microcytic/hypochromic anemia -- from iron deficiency, lead poisoning, or thalassemia
Microcytic/normochromic anemia -- an erythropoietin deficiency from kidney failure
Macrocytic/normochromic anemia -- from chemotherapy, folate deficiency, or vitamin B-12 deficiency

What the risks are Return to top

Excessive bleeding
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Multiple punctures to locate veins

Special considerations Return to top

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.

Update Date: 9/14/2003

Updated by: Corey Cutler, M.D., M.P.H., F.R.C.P.C., Department of Medical Oncology, Dana-Farber Cancer Institute; Instructor in Medicine, Harvard University, Boston, MA. Review provided by VeriMed Healthcare Network.

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