Physiology

PresentationRoll No.#

218, 224, 230, 236, 242, 248

Muhammad Mohsin Ali Dynamo

Topic: Red Blood Cells

Indices and their Interpretation in different types of anemias.

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

(μm ). 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 Coefficient of variation in size distribution of RBCs

o Displayed as a percentageo Normal value: 1 3 ± 1 .5%.o Usual size of RBC is 6-8 µmo Measured as : RDW = (Standard deviation of

MCV ÷ mean MCV) × 100 o Normal Value: Heterozygous Thalassemia (in

case of anemia)o Increased Value: Anisocystosis (RBCs of

unequal sizes)

Practically Determining Blood Indices

Peripheral Blood Smear: 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 examined microscopically. 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:

ANEMIAAnemia 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 Anemia1. Morphologically Classified2. Etiologically Classified

Morphological Characteristics of

RBCs

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:

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.

RBC index Value Normal Value

MCV 70 fl 80-100 fl

MCH 20 pg 27-31 pg

MCHC 28 g/dl 30-36 g/dl

EtiologicalClassification

Type of Anemia Cause Morphological Characteristics of

RBCS

Red Blood Cell Indices

Hemorrhagic Anemia

Acute Blood Loss—after accident Chronic Blood Loss—due to peptic ulcer, hemophilia, prolonged external and internal bleeding

Normocytic, Normochromic  Microcytic, Hypochromic (due to iron deficiency)

MCV, MCHC: within normal range  MCV and MCHC less than normal

Hemolytic Anemia (destruction of RBCS)

Extrinsic (due to external factors)1. Liver Failure2. Renal disorder3. Hyperspleenism4. Burns5. Infections

(hepatitis, malaria)

6. Drugs (penicillin)7. Lead Poisoning Intrinsic (abnormal RBC shape)8. Sickle Cell

Anemia9. Thalassemia

     Normocytic Normochromic       Sickle Shape, normocyticMicrocytic, Hypochromic

     MCV and MCHC values within normal range       MCV values are normalMCV and MCHC values are less

Aplastic Anemia Bone marrow aplasia due toi. Radiationii. Toxic Chemicalsiii. Autoimmune

disorders ()iv. Unknown cause

(idiopathic)

Normocytic, normochromic

MCV and MCHC normal, RBC count less

Anemia of Chronic Diseases

a. Noninfectious inflammatory diseases—rheumatoid arthritis

b. Chronic infectionsc. Chronic Renal

failured. Neoplastic

disorders—Hodgkin’s disease

Microcytic, normochromic

Decreased MCV, MCHC normal

Nutrition Deficiency Anemia (due to deficiency of substance necessary for erythropoiesis)

Iron Deficiency

Vitamin B-12 (Pernicious Anemia) Folic Acid (Megaloblastic anemia) 

Microcytic, hypochromicMacrocytic, hypochromic Macrocytic, normochromic

MCV and MCHC lessMCV more, MCHC lessMCV more, MCHC lessMCV more, MCHC within normal range

Refe

rence

s

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

Questions?