Complete Blood Count (CBC)

It includes:  White blood cell (WBC, leukocyte) count  White blood cell types (WBC differential)  Red blood cell (RBC) count       Hematocrit (HCT, packed cell volume, PCV) Hemoglobin (Hgb) Red blood cell indices Mean Corpuscular Volume Mean Corpuscular Hemoglobin Mean Corpuscular Hemoglobin Concentration Platelet (thrombocyte) count Mean platelet volume (MPV) Red Blood Cell Distribution Width (RDW)

So what are Red Blood Cells Indices?

An index is a quantitative measurement of anything. Therefore a Red Blood Cell Index would mean a quantitative measurement of Red Blood Cells, the amount and the concentration of Hemoglobin in them. Red Blood Cell Indices include: 1. Mean Corpuscular Volume (MCV) 2. Mean Corpuscular Hemoglobin (MCH) 3. Mean Corpuscular Hemoglobin Concentration (MCHC) They were first introduced by Wintrobe in 1929 to define the size (MCV) and hemoglobin content (MCH, MCHC) of red blood cells.

 Red cell indices can be calculated if the values of hemoglobin, hematocrit (packed cell volume), and red blood cell count are known .

MEAN CORPUSCULAR VOLUME (MCV)

 It is the measure of average size or volume of RBCs.

 Expressed in femtoliters (fl; 10^-15 liter) or as cubic microns ( μ m ).

  Normal Value: 87± 7 fl (80-100 fl) Calculated by:    Normal MCV—Normocyte High MCV—Macrocyte (Pernicious and megaloblastic anemia) Low MCV—Microcyte (Iron deficiency anemia)

MCV VALUES AND DIFFERENT TYPES OF ANEMIA

MEAN CORPUSCULAR HEMOGLOBIN (MCH)

 MCH quantifies the amount or weight of hemoglobin per RBC.

 Measured in picograms (pg)  Normal Value: 29 ± 2 picograms (pg) per cell.

 Calculated by:

MEAN CORPUSCULAR HEMOGLOBIN CONCENTRATION (MCHC)

 MCHC indicates the amount of hemoglobin per unit volume.  In contrast to MCH, MCHC correlates the hemoglobin content with the volume of the cell.  Expressed as g/dl of red blood cells or as a percentage value.  Normal values: 34 ± 2 g/dl.

 Calculated by

RBC Distribution Width (RDW)

o o o o o o o Coefficient of variation in size distribution of RBCs Displayed as a percentage Normal value: 1 3 ± 1 .5%.

Usual size of RBC is 6-8 µm Measured as : RDW = (Standard deviation of MCV ÷ mean MCV) × 100 Normal Value: Heterozygous Thalassemia (in case of anemia) Increased Value: Anisocystosis (RBCs of unequal sizes)

Practically Determining Blood Indices

Peripheral Blood Smear:

examined microscopically.  A blood film or peripheral blood smear is a thin layer of blood smeared on a microscope slide and then stained in such a way to allow the various blood cells to be Examination of a blood film stained with Wright’s stain provides information about various types of anemias.  RBCs are 7-8 µm in diameter   Peripheral concentration of Hb, central pallor. Used to determine type of anemia that is present in the patient.

  For instance, the occurrence of hypochromic, microcytic RBCs indicates iron deficiency anemia, that may occur due to chronic blood loss. The presence of macrocytes is often found in patients of megaloblastic anemia due to deficiency of Vitamin B-12 and Folic acid.

Automated Hematology Analyzers:

 A Beckman Coulter counter, using electrical analysis based on Coulter’s principle, is used to perform CBC.

     In this process, a suspension of blood cells is passed through a small orifice or aperture simultaneously with an electrical current. This is known as the sensing zone. In this zone, each particle displaces its own volume of electrolyte. The counter measures this volume change as a pulse, with the height of each pulse being proportional to the volume of the particle.

From this Automated Analyzer, we get the values of RBC indices, which can be interpreted for different kinds of anemias:

ANEMIA

Anemia means deficiency of hemoglobin in the blood, which can be caused by either too few red blood cells or too little hemoglobin in the cells.

Types of Anemia 1. Morphologically Classified 2. Etiologically Classified

1. Normocytic Normochromic:

The MCV and MCHC values of RBCs are normal. But the number of RBCs are less.

2. Macrocytic Hypochromic:

The MCV values are large. The MCHC values are low. Therefore the RBCs appear to be of large size with pale coloration.

3. Macrocytic Normochromic:

The MCV values are again large. However, the MCHC values are normal, so that the RBCs appear large with normal coloration.

4. Microcytic Hypochromic:

The MCV values are less. The MCHC values are also less. As a consequence, the RBCs appear smaller with pale coloration (central pallor is more than 50% of diameter; normally it is 30 40%).

There are NO hyperchromic anemias. In spherocytosis, the MCHC is increased due to loss of membrane and the consequent spherical shape assumed by the cell.

Normocytic Normochromic Macrocytic Normochromic Microcytic Hypochromic Macrocytic Hypochromic

But these were the characteristics of RBCS as they occur in different types of anemias! What are the common types of anemias that show these characteristics?

Why we need to assess Anemias based on red blood cell indices?

Suppose a patient, after undergoing a CBC, comes to a clinician, with the results of MCV, MCHC and MHC as under:

RBC index

MCV MCH MCHC

Value

70 fl 20 pg 28 g/dl

Normal Value

80-100 fl 27-31 pg 30-36 g/dl We evaluate him as being Microcytic and Hypochromic.

Now we wish to identify the cause to administer proper treatment. This is done by carefully planning the clinical causes and morphological characteristics of anemias, as we will be doing next.

Type of Anemia Cause Morphological Characteristics of RBCS Red Blood Cell Indices Hemorrhagic Anemia

Acute Blood Loss—after accident Normocytic, Normochromic MCV, MCHC: within normal range Chronic Blood Loss— due to peptic ulcer, hemophilia, prolonged external and internal bleeding Microcytic, Hypochromic (due to iron deficiency) MCV and MCHC less than normal

Hemolytic Anemia (destruction of RBCS)

Extrinsic (due to external factors) 1.

Liver Failure 2.

Renal disorder 3.

4.

5.

6.

7.

Hyperspleenism Burns Infections (hepatitis, malaria) Drugs (penicillin) Lead Poisoning Normocytic Normochromic MCV and MCHC values within normal range Intrinsic (abnormal RBC shape) 1.

Sickle Cell Anemia 2.

Thalassemia Sickle Shape, normocytic Microcytic, Hypochromic MCV values are normal MCV and MCHC values are less

Nutrition Deficiency Anemia (due to deficiency of substance necessary for erythropoiesis) Iron Deficiency Vitamin B-12 (Pernicious Anemia) Folic Acid (Megaloblastic anemia) Microcytic, hypochromic Macrocytic, hypochromic Macrocytic, normochromic Aplastic Anemia Bone marrow aplasia due to i.

Radiation ii.

Toxic Chemicals iii. Autoimmune disorders () iv. Unknown cause (idiopathic) Normocytic, normochromic MCV and MCHC less MCV more, MCHC less MCV more, MCHC less MCV more, MCHC within normal range MCV and MCHC normal, RBC count less Anemia of Chronic Diseases

a.

b.

c.

d.

Noninfectious inflammatory diseases— rheumatoid arthritis Chronic infections Chronic Renal failure Neoplastic disorders— Microcytic, normochromic Decreased MCV, MCHC normal

1. N Engl J Med 2005;352:1011-23 2. Guyton and Hall, Textbook of Medical Physiology 3. Sembulingam, Essentials of Medical Physiology 4. Walker et al, Clinical Methods: The History , Physical, and Laboratory Examinations.

5. Perkins S., Diagnosis of Anemia