Blood is the fluid connective tissue of the blood. On an average there are about 5 - 6 litres of blood present. To be more precise it is 66ml/kg body weight in females and 70 ml/kg body weight in males.

Blood contains mainly a fluid called plasma in which are suspended cellular elements. Three types of cells - Red Blood Cells or RBC's, White Blood Cells or WBC's and tiny platelets form the cellular element.

 On an average, in a healthy male it should be between 14 - 16 gm % and in a female it should be about 12 - 14 gm %.

Every individual has two types of blood groups. The first is called the ABO - grouping and the second type is called Rh - grouping.

In the ABO - group there are four categories namely A Group, B Group, O Group and AB Group.

In the Rh - Group either the individual is Rh-positive, or Rh-negative.

Thus each and very human being will fall in one of the following groups.
A positive or A negative
B positive or B negative
O positive or O negative
AB positive or AB negative
There are also some sub groups as well as a few other classifications. 

 There are many situations in which patients need blood to stay alive:

• A patient needs blood after a major accident in which there is loss of blood.
• No major surgery is performed without blood as there is bound to be blood loss.
• For surgeries like open heart surgery
• In miscarriage or childbirth, cases the patient may need large amount of blood to be transfused for saving her life and also the child's.
• For patients with blood diseases like severe Anaemias especially Aplastic Anaemias, Leucaemias (blood cancer), Haemophilia (bleeding disorder), Thalassemia etc. repeated blood transfusions are the only solution.
• In many other situations like poisoning, drug reactions, shock, burns, blood transfusion is the only way to save precious human life.

There are three types of blood donors: -

(1) PROFESSIONAL DONORS - They sell their blood, which is of very poor quality and can transmit very dangerous diseases to the recipient. It is illegal to take blood from any professional donor.

(2) REPLACEMENT DONATION - Healthy relatives and friends of the patient give their blood, of any group, to the blood bank. In exchange, the required number of units in the required blood group is given.

(3) VOLUNTARY DONATION- Here a donor donates blood voluntarily. The blood can be used for any patient even without divulging the identity of the donor. This is the best type of blood donation where a motivated human being gives blood in an act of selfless service.

 Any person within the age group of 18 - 60 years with a body weight as minimum 45 kgs, and having hemoglobin content as minimum 12.5 gm%.

Donating blood is a safe process. Needles and bags used to collect blood are used only once and then discarded, making spread of infection to the donor not possible.

The whole process takes about half an hour. It starts with registration, a health history and a mini-physical. Then comes the actual donation, which usually takes less than 10-12 minutes. Afterward, you will be asked to spend a few minutes in the refreshment area where you can have a light refreshment before returning to your normal activities.

 A blood donation equals approximately one pint of blood. The average adult body has 10-12 pints. The vast majority of people will not feel any different because of the donation. A very small percentage may experience temporary dizziness, but some rest and fluids will help you feel better quickly. Your body will replace the lost fluid within 24 hours.