RBC indices
Alternative names:
blood indices; erythrocyte indices; MCH (mean corpuscular hemoglobin); MCHC (mean corpuscular hemoglobin concentration); MCV (mean corpuscular volume); red cell mass measurement
How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet 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.
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 MCV, MCHC, and MCH are derived from the hemoglobin (Hgb), hematocrit (Hct) and red blood cell count (RBC) by mathematical calculations: - MCV = Hct/Hgb
- MCHC = Hgb/Hct
- MCH = Hct/RBC
How to prepare for the test:
Adults:
No special preparation is necessary.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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 (color), of individual cells. These RBC indices are useful in the differential diagnosis of types of anemia.
Anemias are classified on the basis of cell size (MCV) and cell color (MCHC). - MCV less than lower limit of normal: microcytic
- MCV within normal range: normocytic
- MCV greater than upper limit of normal: macrocytic
- MCHC less than lower limit of normal: hypochromic
- MCHC with normal range: normochromic
- MCHC greater than upper limit of normal: hyperchromic
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