Complete Blood Count (CBC)
- A complete blood count (CBC) is a test that gives information about the cells in a patient's blood.
It is one of the most ordered lab tests.
- In the past, the number of cells in the patient's blood was manually counted.
- Nowadays, the use of an automated analyzer.
Automated blood analyzer
- The blood is well mixed and put on a rack in the analyzer.
- The instrument has many different components and can analyze different elements in the blood.
- The cell counting component counts the number and types of different cells in the blood.
- The results are printed out or dispatched to a computer for review.
Component of the CBC:
▪ Red Blood Cells (RBCs).
- RBCs counts
- Hematocrit (Hct)
- Hemoglobin (Hb)
- Blood indices (MCV, MCH, MCHC)
- Red cell distribution width (RDW)
- Reticulocytic count
▪ White Blood Cells (WBCs)and differential.
▪ Platelet count & MPV.
Normal red blood cells values at different ages are:
- Adults:
(males): 4.5 – 5.5 106/mm3
(Females): 3.8-4.8 106/mm3
- Pregnancy: slightly lower than normal adult values
- Newborns: 4.8 - 7.2 106/mm3
- Children: 3.8 – 5.5 106/mm3
Hemoglobin Estimation
The amount of hemoglobin in the blood expressed in gm/dl.
Different methods can be used to estimate hemoglobin concentration, these methods include:
1. Cyanmet Hb (stable, non-oxygen Hb) method using Drabkin’s solution.
2. Sahli’s method.
3. Direct reading using haemoglobinometer
Normal Values for hemoglobin
— Male: 13 to 17 g/dl
— Female: 12 to 16 g/dl
— Pregnancy: 11 - 12 g/dl
— Child: 11.5 to 13.5 gm/dl
— Newborns: 17 to 22 gm/dl (77% of this value is fetal hemoglobin, which drops to approximately 23% of the total at 4 months of age).
Hematocrit (packed cell volume, P.C.V)
- It is the volume of packed RBCs in 100 ml blood expressed in percent.
- Hematocrit can be used as a simple screening test for anemia.
Normal Values for hematocrits:
Male 40-50%
Female 35-45%
Infant 45-65%
RED BLOOD CELL INDICES
Definition
- Red blood cell indices are measurements that describe the size and hemoglobin content of red blood cells.
The indices are used to assist in the differential diagnosis of anemia.
- They have also named red cell absolute values or erythrocyte indices.
- The indices include these measurements:
Mean Corpuscular Volume (MCV)
Mean Corpuscular Haemoglobin (MCH)
Mean Corpuscular Haemoglobin Concentration (MCHC)
- They are usually measured by an automated instrument as part of a Complete Blood Count (CBC).
Mean Corpuscular Volume (MCV)
MCV is the index most often used.
It calculates the average volume of a red blood cell.
Normal value: 80-96 fl.
MCV = Haematocrit (PCV) X 10 / RBC in millions/mm3.
Under a microscope, stained red blood cells with a high MCV look larger than cells with a normal or low MCV.
The MCV categorizes red blood cells by size which is used to classify anemias.
Normal size is normocytic,
Smaller cells are microcytic.
Larger cells are macrocytic.
Mean Corpuscular Hemoglobin (MCH)
The average weight of hemoglobin in red blood cells is measured by the MCH.
The MCH value usually increases or decreases with the increase or decrease of MCV.
Normal value: 27-32 pg
MCH = Hb (g/dl) X 10 / RBC in millions/mm3.
Mean Corpuscular Hemoglobin Concentration (MCHC)
The MCHC determine the average concentration of hemoglobin in a red blood cell.
Normal value: 32-36 g/dl.
MCHC= Hb (g/dl) X 100 / Haematocrit (%)
Cells with too little haemoglobin are lighter in colour with a larger pale area in the centre.
Since there is a physical limit on the amount of hemoglobin that can be contained in a cell, there is no hyperchromic classification.
MCHC is normal in normochromic anemia.
MCHC is decreased in hypochromic anemia.
Normal results for red blood cell indices
MCV 80-96 fl (femtolitres)
MCH 27-32pg (picograms)
MCHC 32-36 g/dl
Red cell Distribution Width (RDW)
The RDW measures the variation in the size of the RBCs (Anisocytosis).
Higher RDW indicates a great variation in size.
Iron-deficiency anemia initially manifests as a difference in red blood cell size distribution, thus showing an increase in RDW.
The normal value of RDW is 11.5-14.5%.
Reticulocytes
- Reticulocytes are immature red blood cells produced by bone marrow and released into the blood flow.
- Reticulocytes are larger than fully mature RBCs and more spherical.
- It circulates in the bloodstream for about 2 days before developing into mature red blood cells.
- Its count provides information about the rate at which the bone marrow is producing red cells.
Reticulocyte count
- Reticulocytes are counted manually with a microscope.
- The reticulocyte count may be expressed as a percentage of total RBCs or as an absolute number of reticulocytes in a given volume of blood.
- The reticulocyte count indicates the presence of a disease or condition but is not directly diagnostic of any one particular disease.
The normal value of reticulocyte:
Adults and children: 0.5-2.5%.
Infants: 2-5%.
Absolute Reticulocytic count: 30,000-130,000 per microliter
Abnormal results:
A low reticulocyte count indicates a defect in bone marrow production.
The increase in reticulocyte count indicates that bone marrow makes more red cells in response to bleeding or hemolysis.
White Blood Cells
Leucocytic count and differential
- It determines the number of white blood cells and the percentage of each type of white blood cell in a person's blood.
- These tests help investigate a variety of illnesses, including infection, allergy, and leukemia.
The total leucocytic count
It varies normally with age, exercise, relationship to a meal, hot bath, high altitudes, and dehydration.
Normal Values:
Adults: 4,000 to 11,000/ mm3.
Children: 8,000 to 11,000/ mm3.
infants: 10,000 to 26,000 /mm3
Differential or "diff" leucocytic count
It is reported in percentages.
1- Neutrophils: 40 - 75% (2,000-7.000/ mm3)
2- Lymphocytes: 20 - 40% (1.500-3.500/ mm3)
3- Monocytes: 2 - 10% (200-1000/ mm3)
4- Eosinophils: 1 - 6% (20-500/ mm3)
5- Basophils: < 2% (20-100/ mm3)
Absolute blood count
By multiplying the percentage of differential leucocytic count with the total number of white blood cells, the absolute number of each type of white cell can be obtained.
Absolute values= total leucocytic count X % / 100
It is more important for diagnosis of diseases.
Platelets (Thrombocytes)
Platelets are the blood cell fragments that are involved in the cellular mechanisms that lead to the formation of blood clots.
Normal platelet Count: 150.000-400.000 /mm3
Mean platelet volume (MPV):
A measurement of the average size of platelets.
Pancytopenia
Pancytopenia is an abnormally low level of all blood cells made by the bone marrow.
This includes a low level of red blood cells (RBCs), white blood cells (WBCs), and platelets.
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