Anemia is a state of reduced red blood cell mass leading to reduced body oxygen carrying capacity.Red cell indexes are useful in the classification of anemia.Anemias are etiologically and morphologically classified.In this article,we will discuss about red cell indices as well as anemia classification.Anemia is defined as the state in which the red blood cell mass decreases below the normal level for the patient’s age and sex.As a result, the oxygen carrying capacity of blood is reduced.It is characterized by reduced hemoglobin, packed red cell volume( PCV) and red blood cell count( RBC).
What are Red cell indices
Red cell indices play a crucial role in anemia classification.These parameters are provided by automated analyzers in well- equipped laboratories.Manual cell counting and further calculation of the indices based on them is not accurate and obsolete.The important red cell indices are:
- Mean Corpuscular Volume (MCV)
MCV is defined as the average red blood cell volume expressed in femtoliters.It is calculated by using the formula:
MCV is determined by the pulse height analysis in the electronic counters.
|Men||92 ± 9 fL|
|Women||92 ± 9 fL|
B. Mean Corpuscular Haemoglobin (MCH)
MCH is the average mass of haemoglobin per erythrocyte expressed in picograms. It is calculated using the formula:
In electronic counters, the MCH is a derivative value based on hemoglobin and RBC count.
|Men||29.5 ± 2.5 pg|
|Women||29.5 ± 2.5 pg|
C. Mean Corpuscular Haemoglobin (MCHC)
MCHC is a measure of hemoglobin concentration in a given volume of packed red cells and expressed as g / L
|Men||330 ± 15 g/L|
|Women||330 ± 15 g/L|
This is a derivative value of Hb and PCV in electronic counters( or MCV and RBC).
D. Red Cell Width or RDW distribution
The RDW is a measure of red cell size or anisocytosis variation. It is derived from the pulse height analysis in electronic counters and can be expressed either as a coefficient of variation
( CV) of the RBC volume or as a standard deviation( in fL).
The normal RDW as variation coefficient( CV) is 12.8 ± 1.2 percent and the standard deviation SD is 42.5 ± 3.5 fl.
Below are the normal values for all red cell indices mcv mch
|XXX||Hb (g/dL)||PCV (L/L)||RBC (x1012/L)||MCV (fL)||MCHC (pg)||RDW (g/L)||MCH (%)|
|Male||14.5±1.5||0.45±0.0||5 5±0.5||87±5||29±2||330±15|| 12.8±1.2|
1.Classification based on Red Cell morphology and Red Cell indices
A. Normocytic Normochromic Anemia
- Here,there is a decrease in hemoglobin concentrations, PCV and RBC.
- MCV, MCH, MCHC, and RDW are normal.
- The blood film shows reduced RBCs appearing in normal size and color.
- Examples include anaemia due to acute blood loss (anemia blood disease), haemodilution, reduced secretion of erythropoietin, and anaemia associated with impaired marrow response.
B. Microcytic Hypochromic Anemia
- The number of hemoglobin, PCV and RBC decreases
- The MCV, MCH and MCHC are reduced. RDW may or may not be raised
- The blood film shows small RBCs( microcytic) with central pallor increase( hypochromic)
- Examples are iron deficiency anemia, chronic anemia, globin synthesis disorders( beta thalassemia minor), sideroblastic anemia, and lead poisoning.
C. Macrocytic Anemia
- Here,there is a decrease in Hemoglobin, PCV and RBC count
- The MCV and MCH increase, the MCHC is normal and the RDW increases. The blood film shows a large number of well hemoglobinized macrocytes.
- Macrocytic anaemia is further subdivided into megaloblastic and non- megaloblastic anaemia.
- Examples of megaloblastic anemia are folic acid or vitamin B12 deficiency, hereditary disorders of DNA synthesis and drug- induced disorders of DNA synthesis.
- Non Megaloblastic anemia may occur because of hypothyroidism, liver disease, alcoholism and aplastic anemia.
2. Classification Based on the Cause of Anemia
A. Due to deficiency of building materials essential for blood production
|Type of Anemia||Cause of Anemia|
|Iron deficiency anemia||red cells are unable to make normal amount of hemoglobin|
|Vitamin B12 and folic acid deficiency||Results in abnormal DNA synthesis leading to megaloblastic anemia.|
|Anemia of protein calorie malnutrition(nutritional anemia)||red cells are unable to make globin chains|
B. Bone marrow disease interfering with normal haematopoiesis(bone marrow anemia)
- Aplastic and hypoplastic anemia
- Leukemia/lymphoma caused by abnormal proliferating cells infiltrating marrow
- Fibrosis of the marrow which could be primary or secondary
- Inflammatory conditions caused by tuberculosis, granuloma formation
C. Anemia due to excessive blood loss(anemia caused by blood loss)
|Acute blood loss||accidents, trauma, surgery, hematemesis|
|Chronic blood loss||gastrointestinal bleeding due to ulcers, cancer, piles, hookworm infestation, genitourinary due to repeated pregnancies, excessive periods.|
D. Anemia due to Increased red cell destruction (Haemolytic anemias)
It could be due to the following
1.RBC defects( Intracorpuscular Defects)
- Red cell membrane defects example Hereditary spherocytosis, elliptocytosis
- Abnormalities of red cell enzymes example G6PD deficiency
- Abnormalities of hemoglobin synthesis
|Decreased globin synthesis||quantitative defect (Example Thalassemias)|
|Abnormal globin synthesis||qualitative defects.Example Sickle cell anemia|
2. Defects outside the RBC (Extracorpuscular defects)
- Immune haemolytic anemias due to alloimmune, autoimmune hemolytic anemia, drug induced
- Parasites – eg malaria
- Bacterial – eg Clostridia
- Venoms – eg snake venoms
- Red cell fragmentation seen in disseminated intravascular coagulation, haemolytic uremic syndrome, march haemoglobinuria, prosthetic heart valves etc.
- Drug induced