It only takes a few minutes but giving blood will help to save someone's life.

As Christmas approaches, the National Blood Service (NBS) is asking people to think about giving blood over the next few weeks.

Donations generally go down at this time of year as people are rushing around buying presents, going out for drinks and parties and preparing for Christmas Day.

The NBS says if people can stop and think and take the time to donate blood, stocks will increase dramatically.

Donated blood is mainly used for transfusions, to replace blood lost in surgery and after accidents. But these are not the only circumstances as they can also be used to treat conditions such as anaemia.

All blood donors are unpaid volunteers whose health is carefully checked to avoid any infections being passed on.

Every unit of donated blood is tested for the presence of certain infections such as HIV and Hepatitis B and C. Any unit which fails is discarded.

The risk of catching hepatitis from a transfusion is very low - about one in 200,000 (you are 25 times more likely to die in a road accident).

The chance of HIV infection due to a blood transfusion is about the same as the risk of being struck by lightning - about one in 10,000,000.

Donated blood will be specially selected to match a person's own blood for the most important blood groups but because red blood cells carry more than 100 different blood groups, an exact match is not possible.

Blood is not generally given whole but is divided into red and white blood cells, platelets and plasma.

Red blood cells are widely used to replace blood lost during surgery or when people haemorrhage. Their main function is to carry oxygen to the tissues.

It is essential to replace lost red cells after such things as accidents, surgery and childbirth.

They are also used in the treatment of all kinds of anaemia which can't be medically corrected, such as when rheumatoid arthritis or cancer is involved, when red cells break down in the newborn and for sickle cell disease. Another use is as pre-op "top-ups" for existing anaemic patients and for burn victims.

White blood cells will attack any viruses or infections which threaten a person's system. They can be given to patients suffering from life-threatening infections whose normal defence mechanisms don't seem to be responding to antibiotics.

Platelets are tiny cells which are crucial in helping blood to clot. People whose platelet levels are low probably suffer a lot from bruising and bleeding.

Platelets can be of huge benefit to people suffering bone marrow failure and leukaemia, following transplants and during chemotherapy treatments.

Plasma is the fluid left when the red and white cells and platelets are taken away. It contains products such as albumin, which is useful when treating someone who has been severely shocked or burned.

It also contains clotting factors such as Factor VII which helps people whose blood does not clot properly.

Plasma is used after obstetric loss of blood (usually childbirth) and during during cardiac surgery.

It is also used to replace clotting factors after massive transfusions or when they're not being sufficiently produced, such as liver disease.

Almost anyone between the ages of 17 and 60 can become a new blood donor. Regular donors still in good health can donate up to the age of 70.

Last year, the NBS collected 2.5 million donations from about 1.9 million donors, which sounds a lot but is only six per cent of the population who are giving two or three times a year.

For more details about giving blood or to find your nearest blood donor session, call 08457 711711 or go to www.blood.co.uk