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 RBC Indices


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: 01/08/2008

: RBC Indices    24 - 3:35


RBC Indices


Red blood cell indices are measurements that describe the size and oxygen-
carrying protein (hemoglobin) content of red blood cells. The indices are used to help in the differential diagnosis of anemia. They are also called red cell absolute values or erythrocyte indices


Anemia includes a variety of conditions with the same outcome: a person's blood cannot carry as much oxygen as it should. A healthy person has an adequate number of correctly sized red blood cells that contain enough hemoglobin to carry sufficient oxygen to all the body's tissues

An anemic person has red blood cells that are either too small or too few in number. As a result, the heart and lungs must work harder to make up for the lack of oxygen delivered to the tissues by the blood

Anemia is caused by many different diseases or disorders. The first step in finding the cause is to determine what type of anemia the person has. Red blood cell indices help to classify the anemias


Certain prescription medications may affect the test results. These drugs include zidovudine (Retrovir), phenytoin (Dilantin), and azathioprine (Imuran)



Anemia has several general causes: blood loss; a drop in production of red blood cells; or a rise in the number of red blood cells destroyed. Blood loss can result from severe hemorrhage or a chronic slow bleed, such as the result of an accident or an ulcer. Lack of iron, vitamin B12, or folic acid in the diet, as well as certain chronic diseases, lower the number of red blood cells produced by the bone marrow. Inherited disorders affecting hemoglobin, severe reactions to blood transfusions, prescription medications, or poisons can cause red blood cells to burst (hemolyze) well before the end of their usual 120-day lifespan

Anemia of any type affects the results of one or more of the common blood tests. These tests are the hematocrit, hemoglobin, and red blood cell count. The hematocrit is a measure of red blood cell mass, or how much space in the blood is occupied by red blood cells. The hemoglobin test is a measure of how much hemoglobin protein is in the blood. The red blood cell count (RBC) measures the number of red blood cells present in the blood. Red blood cell indices are additional measurements of red blood cells based on the relationship of these three test results

The relationships between the hematocrit, the hemoglobin level, and the RBC are converted to red blood cell indices through mathematical formulas. These formulas were worked out and first applied to the classification of anemias by Maxwell Wintrobe in 1934

The indices include these measurements: mean corpuscular volume (MCV); mean corpuscular hemoglobin (MCH); mean corpuscular hemoglobin concentration (MCHC); and red cell distribution width (RDW). They are usually calculated by an automated instrument as part of a complete blood count (CBC). Indices are covered by insurance when medically necessary. Results are available the same day that the blood is drawn or the following day

Mean corpuscular volume (MCV)

MCV is the index most often used. It measures the average volume of a red blood cell by dividing the hematocrit by the RBC. The MCV categorizes red blood cells by size. Cells of normal size are called normocytic, smaller cells are microcytic, and larger cells are macrocytic. These size categories are used to classify anemias

Normocytic anemias have normal-sized cells and a normal MCV; microcytic anemias have small cells and a decreased MCV; and macrocytic anemias have large cells and an increased MCV. Under a microscope, stained red blood cells with a high MCV appear larger than cells with a normal or low MCV

Mean corpuscular hemoglobin concentration (MCHC)

The MCHC measures the average concentration of hemoglobin in a red blood cell. This index is calculated by dividing the hemoglobin by the hematocrit. The MCHC categorizes red blood cells according to their concentration of hemoglobin

Cells with a normal concentration of hemoglobin are called normochromic; cells with a lower than normal concentration are called hypochromic. Because there is a physical limit to the amount of hemoglobin that can fit in a cell, there is no hyperchromic category

Just as MCV relates to the size of the cells, MCHC relates to the color of the cells. Hemoglobin contains iron, which gives blood its characteristic red color. When examined under a microscope, normal red blood cells that contain a normal amount of hemoglobin stain pinkish red with a paler area in the center. These normochromic cells have a normal MCHC. Cells with too little hemoglobin are lighter in color with a larger pale area in the center

These hypochromic cells have a low MCHC. Anemias are categorized as hypochromic or normochromic according to the MCHC index

Mean corpuscular hemoglobin (MCH)

The average weight of hemoglobin in a red blood cell is measured by the MCH. The formula for this index is the sum of the hemoglobin multiplied by 10 and divided by the RBC. MCH values usually rise or fall as the MCV is increased or decreased

Red cell distribution width (RDW)

The RDW measures the variation in size of the red blood cells. Usually red blood cells are a standard size. Certain disorders, however, cause a significant variation in cell size

Obtaining the blood sample

The RBC indices test requires 0.17-24 oz (5-7 ml) of blood. A healthcare worker ties a tourniquet on the person's upper arm, locates a vein in the inner elbow region, and inserts a needle into that vein. Vacuum action draws the blood through the needle into an attached tube. Collection of the sample takes only a few minutes


The doctor should check to see if the patient is taking any medications that may affect test results. The patient does not need to fast before the test


Aftercare consists of routine care of the area around the puncture mark. Pressure is applied for a few seconds and the wound is covered with a bandage.


The primary risk is mild dizziness and the possibility of a bruise or swelling in the area where the blood was drawn. The patient can apply moist warm compresses

Normal results

Normal results for red blood cell indices are as follows:
MCV 82-98 fl (femtoliters)
MCHC 31-37 g/dl
MCH 26-34 pg (picograms)
RDW 11.5-14.5%.

Abnormal results

The category into which a person's anemia is placed based on the indices provides a significant clue as to the cause of the anemia, but further testing is needed to confirm a specific diagnosis

The most common causes of macrocytic anemia (high MCV) are vitamin B12 and folic acid deficiencies. Lack of iron in the diet, thalassemia (a type of hereditary anemia), and chronic illness are the most common causes of microcytic anemia (low MCV). Normocytic anemia (normal MCV) can be caused by kidney and liver disease, bone marrow disorders, or excessive bleeding or hemolysis of the red blood cells

Lack of iron in the diet and thalassemia are the most common causes of hypochromic anemia (low MCHC). Normocytic anemias are usually also normochromic and share the same causes (normal MCHC)

The RDW is increased in anemias caused by deficiencies of iron, vitamin B12, or folic acid. Abnormal hemoglobins, such as in sickle cell anemia, can change the shape of red blood cells as well as cause them to hemolyze. The abnormal shape and the cell fragments resulting from hemolysis increase the RDW. Conditions that cause more immature cells to be released into the bloodstream, such as severe blood loss, will increase the RDW. The larger size of immature cells creates a distinct size variation

Key Terms


A variety of conditions in which a person's blood can't carry as much oxygen as it should due to a decreased number or size of red blood cells


A descriptive term applied to a red blood cell with a decreased concentration of hemoglobin


A descriptive term applied to a larger than normal red blood cell

Mean corpuscular hemoglobin (MCH)

A measurement of the average weight of hemoglobin in a red blood cell.
Mean corpuscular hemoglobin concentration (MCHC)
The measurement of the average concentration of hemoglobin in a red blood cell

Mean corpuscular volume (MCV)

A measure of the average volume of a red blood cell


A descriptive term applied to a smaller than normal red blood cell


A descriptive term applied to a red blood cell with a normal concentration of hemoglobin


A descriptive term applied to a red blood cell of normal size

Red blood cell indices

Measurements that describe the size and hemoglobin content of red blood cells

Red cell distribution width (RDW)

A measure of the variation in size of red blood cells




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Mean Corpuscular Volume (MCV)

1-Normal (Units in femtoliters = 10^-15 liters)


1.MCV cutoffs vary from age to age
2.MCV cutoffs also vary per reference

B.MCV Normal Range

1.Newborn: 95 to 121 fl
2.Ages 6 months to 2 years: 70 to 86 fl
3.Ages 12 to 18 years

a.Boys: 78 - 98
b.Girls: 78 - 102

4.Age over 18 years: 78 to 98 fl

C.MCV Cutoffs for Microcytic Anemia

1.Age 1-2 years: <77 fl (CDC)
2.Age 3-5 years: <79 fl (CDC)
3Age 6-11 years: <80 fl (CDC)
4.Age 12-15 years: <82 fl (CDC)
5.Age >15 years: <85 fl (CDC)

a.Recommended adult microcytic MCV cutoff varies
b.Some sources advocate MCV <78 and others <82

2- Calculations

D.MCV = 10 x (Hematocrit / Red Blood Cell Count)

E.Mentzer Index = MCV / RBC Count

1.Ratio <13: Thalassemia
2.Ratio >13: Iron Deficiency Anemia, Hemoglobinopathy
II.Increased (Macrocytic: implies RBC Maturation defect)

A.Vitamin B12 Deficiency
B.Folic Acid deficiency
C.Alcohol Liver disease
E.Marrow aplasia

III.Decreased (Microcytic: implies Abnormal Hgb Synthesis)

A.Iron Deficiency Anemia
D.Anemia of Chronic Disease
E.Sideroblastic Anemia
F.Chronic Renal Failure
G.Lead Poisoning

RedCell Distribution Width (RDW)

I.Indications: Anemia Evaluation

A.Iron Deficiency Anemia from other Microcytic Anemias
B.May increase before MCV becomes abnormal


A.Measures size variability of Red Blood Cell population

A.Range: 11.5-14.5%

IV.Normal Red Cell Distribution Width (RDW)

A.Mean Corpuscular Volume (MCV) Increased

1.Aplastic Anemia

B.Mean Corpuscular Volume (MCV) Normal

1.Anemia of Chronic Disease
2.Acute blood loss
4.Chronic Lymphocytic Leukemia (CLL)
5.Chronic Myelogenous Leukemia (CML)
7.Normal variant

C.Mean Corpuscular Volume (MCV) Decreased

1.Anemia of Chronic Disease
2.Thalassemia (heterozygous)

V.Increased Red Cell Distribution Width (RDW)

A.Mean Corpuscular Volume (MCV) Increased

1.Vitamin B12 Deficiency
2.Folate Deficiency
3.Immune Hemolytic Anemia
4.Liver disease

B.Mean Corpuscular Volume (MCV) Normal

1.RDW increases before MCV becomes abnormal
a.Early Iron Deficiency Anemia
b.Early Vitamin B12 Deficiency
c.Early Folate Deficiency

2.Anemic globinopathy

C.Mean Corpuscular Volume (MCV) Decreased

1.Iron Deficiency Anemia
2.RBC fragmentation
4.Thalassemia intermedia
5.Hematocrit (HCT)


A.Hct = Mean Corpuscular Volume x Red Blood Cell Count
II.Normal Values per age (-2 SD to +2 SD)
A.Birth: 42 to 64% (mean 51%)
B.Age <1 month: 31 to 67% (mean 44%)
C.Age 1-2 months: 28 to 55% (mean 35%)
D.Age 2-6 months: 28 to 42% (mean 36%)
E.Age 0.5 - 2 years: 33 to 40% (mean 36%)
F.Age 2 to 6 years: 34 to 40% (mean 37%)
G.Age 6-12 years: 35 to 45% (mean 40%)


1.Age 12-18 years: 36 to 46% (mean 41%)
2.Age >18 years: 36 to 44% (mean 41%)
1.Age 12-18 years: 37 to 49% (mean 43%)
2.Age >18 years: 41 to 50% (mean 47%)

III.Anemia Cutoffs


1.Age 12-14 years: <37.3%
2.Age 15-17 years: <39.7%
3.Age >17 years: <38% (WHO) or <39.9% (CDC)

B.Women (Non-pregnant, non-lactating)

1.Age 12-14 years: <35.7%
2.Age 15-17 years: <35.9%
3.Age >17 years <35% (WHO) or <35.7% (CDC)

C.Women in Pregnancy (CDC Guidelines <5th percentile)

1.First Trimester: <33.0%
2.Second Trimester: <32.0%
3.Third Trimester: <33.0%

D.Children (CDC Guidelines <5th percentile)

1.Age 1-2 years: <32.9%
2.Age 2-5 years: <33.0%
3.Age 5-8 years: <34.5%
4.Age 8-11 years: <35.4%

IV.Increased Hematocrit


B.Profound diuresis

1.Burn Injury

D.Polycythemia Vera

E.High Altitude

V.Decreased Hematocrit

A.See Anemia

B.Plasma Volume expansion with constant RBC mass


C.Recovery stage after Acute Hemorrhage

1.Hematocrit lags blood loss (not reliable indicator)

Mean Corpuscular Hemoglobin (MCH)

Mean Corpuscular Hemoglobin concentration (MCHC)


A.Not as useful as other indices for Anemia Evaluation

B.More useful indices

1.Hemoglobin or Hematocrit
2.Mean Corpuscular Volume (MCV)
3.Red Cell Distribution Width (RDW)


A.Mean Corpuscular Hemoglobin (MCH)
1.MCH = (10 x Hemoglobin) / (Red Blood Cell Count)
B.Mean Corpuscular Hemoglobin Concentration (MCHC)
1.MCHC = (Hemoglobin x 100) / (Hematocrit)


A.Mean Corpuscular Hemoglobin (MCH)
1.Normal: >30 pg/cell
2.Abnormal: <30 pg/cell

a.Suggests abnormal Hemoglobin synthesis
B.Mean Corpuscular Hemoglobin Concentration (MCHC)

1.Normal: 28 - 33%
2.Low (< 28%): Iron Deficiency Anemia
3.High (> 33%): Spherocytosis or unstable Hemoglobin



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