Red Blood Cell (RBC):- Part 4 – Red Blood cell Indices

Sample

1. For Blood indices, the best sample is EDTA blood.
2. Collect the blood in the lavender top tubes.
3. Transport the blood to the lab where blood is run in the hematology analyzer for the calculation of blood indices.
4. Blood is stable for 6 hours at 25 °C and for 24 hours at 4 °C.
5. Fetal blood is collected percutaneous from the umbilical area.

Purpose of the test (Indications)

• These tests are useful for the diagnosis of the various types of Anemia.

Precautions

1. The abnormal size of RBC may affect indices.
2. Increased count of WBC will affect the indices.
3. Increased reticulocytes count leads to abnormally high MCV.
4. The presence of cold agglutinins gives false increased values of MCH, MCHC, and MCV.

Definition

• Red cell indices define the size and contents of hemoglobin in Red cells.

Mean corpuscular volume (MCV): 

Definition:

This is the best index for classifying anemia. This is the average volume of red blood cells and measured in cubic micrometers (µ³, femtoliter fL). This indicates the cell size of RBCs.

• Calculation:
• MCV is calculated by dividing hematocrit by total RBC count.
  

  MCV formula and calculation

Normal MCV

• Adult (all ages) = 80 to 95 fL
• Newborn = 96 to 108 fL

1. On the basis of MCV:
   • Macrocytes when MCV value is high, e.g. in Megaloblastic anemia, due to vit B and folic acid deficiency.
   • Microcytes when the MCV is decreased seen in iron deficiency anemia and thalassemia.
2. In microcytic anemia, MCV is 50 to 82 fL.
3. In normochromic normocytic anemia, MCV is 82 to 98 fL.
4. In macrocytic anemia, MCV is 100 to 150 fL (>100 fL).

Mean corpuscular hemoglobin (MCH):

Definition:

• This is the mean of the average amount of hemoglobin in red blood cells or this is the average weight of hemoglobin, in absolute units, in the RBCs.
• The result gives the average content of the hemoglobin per RBC in picograms (pg).
• The MCH value is usually higher in the newborns and infants because their MCV is higher than the adults.

Calculation :

 

• Generally, macrocytes will have more hemoglobin and microcytes will have less hemoglobin. So the values resemble those of MCV.
• Normal MCH
  • Adult ( all ages ) = 27 to 31 pg
  • Newborn = 32 to 34 pg

Mean corpuscular hemoglobin concentration (MCHC):

Definition:

• • This is the average concentration of or percentage of hemoglobin in each individual red blood cells.
    • It is the ratio of the weight of hemoglobin to the volume of the RBCs.
  • MCHC is the most useful for monitoring the treatment of anemia.
  • Calculation:
    • This is calculated by dividing the hemoglobin concentration by hematocrit.
      

      MCHC formula and calculation

• Interpretations:
  1. Hypochromic When MCHC is decreased and then there is a deficiency of hemoglobin (in iron deficiency anemia and thalassemia).
  2. Normochromic when the values are normal (In hemolytic anemia).
  3. Hyperchromic when MCHC value is increased and RBC cannot accommodate more than 37 g/dl (seen in spherocytosis, newborn and infants).
• Normal MCHC
  • Adult all ages = 32 to 36 g /dl (32 to 36%)
  • Newborn = 32 to 33 g /dl (32 to 33%)

Red blood cell distribution width (RDW):

1. Definition:
   1. This is the coefficient of the RBC volume distribution.
   2. This indicates variation in the size of RBC.
2. This is calculated by the machine using MCV and RBC values.
   1. This is an indicator of anisocytosis.
   2. This is helpful for the diagnosis of hematological disorders and monitoring the response to therapy.
   3. This is also helpful in distinguishing iron-deficiency anemia (RDW increased), from the hemoglobinopathies (RDW normal).
3. Calculation: 
   

   RDW formula and calculation

• Normal RDW
  • Adult = 11% to 14.5%

Anemias are defined based on cell size (MCV), amount of Hb, and (MCH):

Parameter		Diagnosis
MCV fL	Less than the lower limit of normal	Microcytic  anemia
	Within normal range	Normocytic anemia
	Greater than the normal	Macrocytic anemia
MCH pg	Less than the lower limit of normal	Hypochromic anemia
	Within the normal limit	Normochromic anemia
	Greater than the upper limit of normal	Macrocytic anemia

Classification of anemia on the basis of MCV and MCHC:

Type of anemia	MCHC%	MCV fL	Causes
Normocytic/normochromic	32 to 36	80 to 100	From blood loss, sepsis, tumors, aplastic anemia, and prosthetic heart valve
Microcytic/hypochromic	<32	<80	Iron deficiency, lead poisoning, and thalassemia
Microcytic/normochromic	32 to 36	<80	Due to deficiency of erythropoietin from kidney failure
Macrocytic/normochromic	32 to 36	>100	Chemotherapy, folate deficiency or vitamin B12 deficiency, hydantoin therapy

MCV:

1. Increased in:
   1. Pernicious anemia (vit B12 deficiency).
   2. Folic acid deficiency.
   3. Antimetabolite treatment.
   4. Chronic liver disease.
   5. Alcoholism.
2. Decreased in:
   1. Iron deficiency anemia.
   2. Thalassemia.
   3. Chronic diseases.

MCH:

1. Increased in:
   1. Macrocytic anemias.
   2. Newborn.
2. Decreased in:
   1. Microcytic anemias.
   2. Hypochromic anemia.

MCHC:

1. Increased in:
   1. Spherocytosis.
   2. Newborn and infants.
2. Decreased in:
   1. Iron deficiency anemia.
   2. Thalassemia.
   3. Microcytic anemia with chronic blood loss.

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