RBC indicesDefinition: 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.
Alternative Names: Erythrocyte indices; Blood indices; Red cell mass measurement; MCH (mean corpuscular hemoglobin); MCHC (mean corpuscular hemoglobin concentration); MCV (mean corpuscular volume)
How the test is performed: 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: 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:
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: 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: - MCV: 80 to 100 femtoliter
- MCH: 27 to 31 picograms/cell
- MCHC: 32 to 36 grams/deciliter
What abnormal results mean: Anemias have been classified as follows:
What the risks are: - 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: 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.
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