Blood is the red coloured fluid flowing continuously in our body’s circulatory system. It 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.
The total amount of blood in the human body can vary with several factors, like age, sex, health condition, body type, etc. However, for an average adult, the volume of blood in his/her body is 7-8% of the body weight (The amount of blood would vary between 5 to 6 litres for an average adult).
Most people can give blood. As long as you are fit and healthy, weigh over 7 stone 12 lbs (50kg) and are aged between 17 and 66 (up to 70 if you have given blood before) you should be able to give blood. If you are over 70, you need to have given blood in the last two years to continue donating. However, If you are female, aged under 20 years old and weigh under 65kg (10st 3lb) and are under 168cm in height, we need to estimate your blood volume before donating.
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. Rh is a factor called as Rhesus factor that has come to us from Rhesus monkeys. It refers to a protein on the red blood cells (Protein present: Rh-positive; Protein absent: Rh-negative). Thus, each and every 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 and other classifications which have not been discussed here.
Frequency of Blood Groups
O+ 1 person in 3 O- 1 person in 15
A+ 1 person in 3 A- 1 person in 16
B+ 1 person in 12 B- 1 person in 67
AB+ 1 person in 29 AB- 1 person in 167