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The Theory Behind Complete Blood Count!

Written and reviewed by
Dr. Jagdish Prasad Mehrotra 91% (1750 ratings)
MBBS, D.P.H
General Physician, Gurgaon  •  44 years experience
The Theory Behind Complete Blood Count!

Complete blood count (CBC):

CBC provides information of the circulating blood & Screen for a wide range of conditions and diseases

  • Help diagnose various conditions, such as anaemia, infection, inflammation, bleeding disorder or leukaemia
  • Monitor the condition and/or effectiveness of treatment after a diagnosis has been established
  • Monitor treatment that is known to affect blood cells, such as chemotherapy or radiation therapy

 Human body is made up of cells and water. Many of the cells group together and form the skin, muscle, bones and organs like Heart, Lungs & Kidney.

Some very special and important cells move throughout the body by circulating in the blood which provides Oxygen to all these stationary cells in the body. These help them to fight against the infection, stop bleeding after an injury.

EVALUATION:  Three types of cells circulate in our body.

  1. WHITE BLOOD CELLS
  2. REDBLOOD CELLS.
  3. PLATLETS.

A. WHITE BLOOD CELLS (WBC):

These cells represent the defence system of body i.e. fight infection and cancer. It also plays role in allergies and inflammation. 

Types of WBC:

  1. NEUTROPHIL: Neutrophils are cells that protect the body from bacterial infections. They move toward bacteria and then swallow them up so the bacteria cannot harm the body.
  2. LYMPHOCYTE: Lymphocytes are cells that protect the body against viruses, bacteria, and fungi. One type of lymphocyte (B-cell) produces antibodies that attack and destroy the bacteria and viruses. Another type of lymphocyte (T-cell) can directly attack viruses and bacteria and can stimulate the B-cells to produce antibodies
  3. MONOCYTES: Monocytes are cells that consume dead or damaged cells. They are the “clean-up crew”.
  4. EOSINOPHIL: Eosinophils are cells that kill parasites and contribute to allergic reactions.
  5. BASOPHIL: Basophils are cells that release histamines during allergic reactions.
  6. OTHERS: Promyelocytes, Metamyelocytes, Blasts, etc. are not normally appear in the blood. In the presence of any of these cells indicates a need for follow-up .

EVALUATION OF WBC:

Low count of WBC is called Leukopenia. The causes of low count are -

  1. Dietary deficiency.
  2. Autoimmune condition.
  3. Sever infection
  4. Lymphoma or other cancer that spread in bone marrow
  5. Bone marrow disorders or damage
  6. Disease of immune system

High count of WBC called Leucocytosis. The causes of high count are-

  1. Infection most commonly bacterial or viral
  2. Inflammation
  3. Leukaemia
  4. Allergy
  5. Tissue death
  6. Intense exercise or sever stress.

 

B. RED BLOOD CELLS (RBC)

These cells transport oxygen from the lungs to the rest of body. These oval shaped cells contain haemoglobin, the protein that binds oxygen while it is carried to all stationary cells in the body i.e., cells in the skin, muscle, bone and organ. The chemical process converts the nutrients found in food into energy requires oxygen. All stationary cells require energy to function; thus, they need oxygen and dependent on the RBCs to transport it.

Haemoglobin: It is an iron rich protein.

  • It carries oxygen.
  • It makes the blood red.
  • Normal range in Male: 13.5 to 17.5 grams per decilitre
  • Normal range in Female: 12.0 to 15.5 gram per decilitre

Low Haemoglobin: This can occur due to

  • Body produces fewer RBC’s than usual
  • Body destroys RBC’s faster than they can produce
  • Blood loss.

Following conditions produce fewer RBC’s -

  1. Aplastic anaemia
  2. Cancer
  3. Drugs like Anti-retroviral used in HIV infection, Chemotherapy of cancer
  4. Chronic kidney disease
  5. Cirrhosis of liver
  6. Hodgkin’s lymphoma
  7. Hypothyroidism
  8. Iron deficiency anaemia
  9. Leukaemia
  10. 10. lead poisoning
  11. 11.Multiple myeloma
  12. 12. Myelodysplastic syndrome
  13. 13.Non-Hodgkin’s lymphoma
  14. 14. Vitamin deficiency anaemia
  15. Following conditions destroy RBC’s faster
  16. Splenomegaly
  17. Haemolysis
  18. Porphyria
  19. Sickle cell anaemia
  20. Thalassemia
  21. Vasculitis (Blood vessels inflammation)

Other cause of low Haemoglobin count

Bleeding from a wound, digestive tract, ulcers, cancer, Haemorrhoids and menorrhagia (heavy menstrual bleeding)

High Haemoglobin count: It occurs when your body requires increased oxygen -carrying capacity

  • Smoking
  • High altitude
  • Poor heart and lung function ( low blood oxygen levels increase RBC’s production)
  • Bone marrow produces too many RBC’s
  • Consumption of drugs or Hormones e.g. Erythropoietin (EPO) stimulates RBC’s production; injection used for athletic performance

Other cause of high hemoglobin in which the body requires an increased oxygen-carrying capacity.

  • Congenital heart disease in adults
  • COPD (chronic obstructive pulmonary disease)
  • Dehydration
  • Emphysema
  • Heart failure
  • Kidney cancer
  • Liver cancer
  • Polycythemia vera

 

HAEMATOCRIT / Packed cell volume (PCV): It is the measurement by centrifugation of blood. It reflects the ratio of the volume of red blood cells to the total volume of blood or Space occupied by the RBCs.

Normal range in Male: 40 .7% to 50.3%

Normal range in Female: 36.1% to 44.3%

Cause of Low PCV/ Haematocrit or anaemia

  • Bleeding (Ulcers, Trauma, Colon Cancer, Internal bleeding)
  • Destruction of RBCs (Sickle Cell Anaemia, Splenomegaly)
  • Decreased Production of RBCs (Bone marrow suppression, Cancer, Drugs)
  • Nutritional Problems (Low Iron, B12, Folate and Malnutrition)
  • Overhydration (Polydypsia, Intravenous overhydration)

           Cause of High PCV/ Haematocrit or anaemia

  • Dehydration (Heat exhaustion, No available source of fluids)
  • Low availability of Oxygen (Smoking, High altitude , Pulmonary fibrosis)
  • Genetic (Congenital Heart disease)
  • Erythrocytosis (Overproduction of RBCs by bone marrow or Polycythemia vera)

 

  • MEAN CORPUSCLE VOLUME (MCV): It reflects the average size of RBCs.

Low MCV reflect small sized RBCs

High MCV reflect Large sized RBCs

  • MEAN CORPUSCULAR HAEMOGLOBIN (MCH): It reflects the average concentration of haemoglobin in a single red blood cell.

Low MCH reflect low haemoglobin concentration

High MCV reflect high haemoglobin concentration

  • MEAN CORPUSCULAR HAEMOGLOBIN CONCENTRATION (MCHC): It reflects the ratio of MCH AND MCV

Low MCHC shows the Thalassemia (Inherited Blood Disorder) microcytic hypochromic anaemia i.e. RBCs are smaller than usual and have decreased level of haemoglobin. It can be caused by

  • Lack of iron
  • Poor absorption of iron due to disease like CELIAC DISEASE, CHRON’S DISEASE AND GASTRIC BYPASS SURGERY
  • CHRONIC LOW-GRADE BLOOD LOSS LIKE IN PEPTIC ULCER OR LONG MENSTURAL CYCLE.
  • HAEMOLYSIS OR PREMATURE DESTRUCTION OF RBCs OVER TIME
  • CANCER CAUSING INTERNAL BLOOD LOSS.
  • HOOKWORM INFECTIONS
  • LEAD POISOINING.

High MCHC reflects more concentrated haemoglobin in red blood cells. It can occur in conditions where red blood cells are fragile or destroyed leading to haemoglobin being present outside te red blood cells. it can be caused by

  • Autoimmune haemolytic anaemia. In which body develops an antibody that attack your red blood cells. It can be idiopathic autoimmune haemolytic anaemia / Lupus lymphoma/ penicillin reaction.
  • Hereditary spherocytosis. It is a genetic disease in which mutation affects the red blood cell membrane and make it more fragile and prone to destruction.
  • Severe burns often have haemolytic anaemia.

 

1. RED CELL DISTRIBUTION WIDTH (RDW): It reflects the degree of variation in size of the RBCs. Normal red blood cells maintain a standard size of 6-8 micrometres. If cells are larger RDW values will have higher numbers. This test is indicated if one has following problem.

  • Anaemia
  • Iron and vitamin deficiency
  • Family history of blood disorder such as sickle cell anaemia
  • Significant blood loss
  • Disease that affects the red blood cells
  • Chronic illness such as HIV / AIDS.

                RDW test diagnose

  • Types of anaemia
  • Thalassemia
  • Diabetes mellitus
  • Heart disease
  • Liver disease
  • Cancer

Normal Range of RDW: 10.2% - 14.5% (39.0 – 46.0)

Low RDW: Body is not producing enough RBC  It indicate

  • Macrocytic Anaemia: Red blood cells are larger than average. Indicate deficiency of folate or vitamin B12.
  • Microcytic Anaemia: Red Blood Cells are smaller than average. It indicates deficiency of Iron. It also suggests Thalassemia.

High RDW:

The possible cause can be asses by comparison with MCV

  1. High RDW and MCV: Haemolytic anaemia, Megaloblastic anaemia, Lack of vitamin B12. Indicate chronic Liver Disease
  2. High RDW and low MCV: Iron deficiency anaemia or Microcytic anaemia, Thalassemia intermedia.
  3. High RDW and Normal MCV: Beginning stages of Vitamin B12 or Folate Deficiency, Beginning stage of Iron deficiency Anaemia. Indicate Chronic Liver Disease.

 

2. Platelets: Platelet is vital for the normal clotting.

EVALUATION OF Platelet:

Low count of Platelet is called Thrombocytopenia. The causes of low count are –

  1. Viral infection including Dengue.
  2. Platelet autoantibody
  3. Drugs
  4. Cirrhosis
  5. Autoimmune disease
  6. Sepsis
  7. Leukaemia
  8. Myelodysplasia (production of blood cells disturbs)

High count of Platelet is called Thrombocytosis. The causes of high count are-

  1. Cancer
  2. Rheumatoid arthritis
  3. Iron deficiency anaemia
  4. Myeloproliferative disorder (Disease of bone marrow and blood)

Mean Platelet Width (MPV): It is calculation of average size of Platelets. Platelets are produced in the Bone marrow and released into the blood stream. Larger Platelets are usually young and more recently released from the bone marrow. smaller platelets are more likely to have been in circulation for few days. Low Platelet count and high MPV level suggests that that the bone marrow is rapidly producing platelets this is because older platelets are being destroyed so the bone marrow compensate.

High MPV may be associated (Depends on other CBC result):

Cancer

Several types of cancer e.g. Lung, ovarian, endometrial, colon, kidney, stomach, pancreatic, and breast cancer

Warning signs of cancer are:

  1. Skin changes
  2. Breast changes
  3. Thickening skin or lump on or under your skin
  4. Hoarseness or cough that doesn’t go away
  5. Changes in bowel habit
  6. Trouble swallowing
  7. Weight gain or loss for no reason
  8. Abdominal pain
  9. Unexplained night sweats
  10. Unusual bleeding or discharge in urine or stool
  11. Feeling weak or tired
  12. Hyperthyroidism
  13. Heart disease
  14. Diabetes
  15. Vitamin D deficiency
  16. High blood pressure
  17. Stroke
  18. Atrial fibrillation

Low MPV may be associated (Depends on other CBC result):

  • Inflammatory bowel disease, Crohn’s disease or ulcerative colitis
  • Cytotoxic medication
  • Aplastic anaemia.

Platelet Distribution Width (PDW): It reflects how uniform platelets ars in size.

  • Reference range of platelet distribution width is: 10%-18%

Low value of PDW:

A low value indicates uniformity in size of platelets. This may also be an indication that there is a disorder present which is affecting the bone marrow and how it is able to produce platelets. Viral infections will typically produce this result, such as measles, hepatitis, or mononucleosis. Certain drugs and cancers can also cause this result.

High value of PDW:

  • A high value indicates increased variation in the size of the platelets, which may mean that a condition is present that is affecting platelets. There are numerous younger platelets and numerous older platelets in the same sample. This may be an indication that some sort of disorder has affected the bone marrow or the platelets and further testing may be required. Certain cancers, anaemia, and inflammatory conditions typically cause this result, as will some infectious diseases or the use of birth control pills.
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