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Red Cell Indices

Using the results of the red blood cell (RBC) count, hematocrit, and total hemoglobin tests, red cell indices (erythrocyte indices) provide important information about the size, hemoglobin concentration, and hemoglobin weight of an average RBC.

Purpose

• To aid diagnosis and classification of anemias.

Patient preparation

• Explain to the patient that this test helps determine if he has anemia.
• Tell him that a blood sample will be taken. Explain who will perform the venipuncture and when.
• Reassure him that drawing a blood sample will take less than 3 minutes.
• Explain that he may feel slight discomfort from the tourniquet pressure and the needle puncture.

Procedure and posttest care

• Perform a venipuncture, and collect the sample in a 7-ml lavender-top tube.
• If a hematoma develops at the venipuncture site, apply warm soaks.

Precautions

• Completely fill the collection tube, and invert it gently several times to adequately mix the sample and the anticoagulant.
• Handle the sample gently to prevent hemolysis.

Reference values

The indices tested include mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC).

MCV, the ratio of hematocrit (packed cell volume) to the RBC count, ex­presses the average size of the erythrocytes and indicates whether they are undersized (microcytic), oversized (macrocytic), or normal (normocytic). MCH, the hemoglobin-RBC ratio, gives the weight of hemoglobin in an average red cell. MCHC, the ratio of hemoglobin weight to hematocrit, defines the concentration of hemoglobin in 100 ml of packed RBCs. It helps to distinguish normally colored (normochromic) RBCs from paler (hypochromic) RBCs.

The range of normal red cell indices is as follows:

• MCV: 82 to 98 um3
• MCH: 26 to 34 pg/cell
• MCHC: 31 to 37 g/dl

Key:

MCV = Mean corpuscular volume

MCH = Mean corpuscular hemoglobin

MCHC = Mean corpuscular hemoglobin concentration

Abnormal findings

Low MCV and MCHC indicate microcytic, hypochromic anemias caused by iron deficiency anemia, pyridoxine­responsive anemia, or thalassemia. A high MCV suggests macrocytic anemias caused by megaloblastic anemias, due to folic acid or vitamin B12 deficiency, inherited disorders of deoxyribonucleic acid synthesis, or reticulocytosis. Because MCV reflects the average volume of many cells, a value within the normal range can encompass RBCs of varying size, from microcytic to macrocytic.

Interfering factors

• Failure to use the proper anticoagulant or to adequately mix the sample and the anticoagulant.
• Hemolysis due to rough handling of the sample.
• Hemoconcentration due to prolonged tourniquet constriction.
• High white blood cell count (false­high RBC count in semiautomated and automated counters, invalidating MCV and MCHC results).
• Diseases that cause RBCs to agglutinate or form rouleaux (false-low RBC count).

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