WE HAVE all seen the National Blood Service adverts on TV.

Give blood and you could save car crash victims, prolong a cancer patient's life or help someone recover from an operation - they are all well-known facts.

Making a donation only takes 15 minutes, and about 60 per cent of the population say they want to start giving blood.

So it is surprising to know that only six per cent of us actually get round to doing it.

Brian Shackleton, of Sinnington, near Pickering, regularly donates blood in memory of his late wife Alwyn, who received at least 307 units while she battled leukaemia.

Brian, 69, said aims to donate a total of 100 units while he remains fit.

"The number of people who say they intend to give blood is amazing," he said.

"If only one day they will turn their good intentions into practice, it would make such a difference."

Hospitals in York need over 50 units of blood a day, while hospitals throughout Yorkshire require 800.

Donation sessions are held regularly throughout the region, and no appointments are needed.

Vicki Hutchinson, of the National Blood Service (NBS), said people often found it interesting to know what happened to their blood once it left their body.

She said: "Before any donation can be taken, a donor completes a health check form and completes a finger prick test to make sure they're not anaemic. They then give 470ml of blood and a few cubic centimetres are drawn off in the beginning and put in three test tubes as samples for testing."

While potential donors are given tea and biscuits, the blood is transported to processing laboratories while the health check forms are sent to the donor records department.

Lab staff take delivery of the blood and a data stick containing the day's donor and donation information.

Donations needed for platelets are processed immediately because of their short shelf life, while bar-coded blood packs are scanned into the computers.

"Tracing donations back to donors is vital and tracing a donation at any part of its journey is equally vital," said Vicki.

"If a donor calls the NBS to say they are feeling unwell or for example has caught measles since donating, their donation can then be found and removed."

The blood is entered onto the system, but by this time the processing has already begun.

White cells are removed from the blood to reduces the risk of vCJD.

The blood is separated into three distinct layers using a spinning machine.

The plasma rises to the top and the red cells settle at the bottom.

The platelets and any remaining white cells are in the middle; a layer known as the buffy coat.

Meanwhile, blood samples are tested for type, rare blood group antibodies, and diseases such as hepatitis B, hepatitis C, HIV and syphilis.

The results are automatically downloaded onto a computer and entered onto the donor's individual record.

Blood, arranged by its group, is stored in vast walk-in cold rooms. Red cells can be kept for 35 days at this temperature.

Platelets only last for five days and at 22 degrees centigrade.

The platelets are kept on special moving shelves to stop the sticky cells from bunching together.

After storage, the blood is sent to hospitals to treat the thousands of patients who need blood every day.

If you are aged between 17 and 60 years of age (17 to 70 for regular donors), in general good health and weigh more than 50kg, you could donate. For more information go to www.blood.co.uk, or for details of local blood donor sessions phone 0845 7711 711.

:: What is your donation used for?

Whole blood

This is mainly used in instances of severe blood loss. It is almost always separated into individual components.

Plasma

Fresh frozen plasma is used after obstetric loss of blood (which is usually childbirth), during cardiac surgery, and to reverse anti-coagulant treatment. It is also used after massive transfusions.

Processed plasma

Factor VIII is used in the treatment of haemophilia and to help produce stronger antibodies against diseases like tetanus, hepatitis, chickenpox and rabies. It also helps generate anti-D which is used for Rh negative pregnant women carrying Rh positive babies. The albumin contained in plasma is extremely beneficial for burn victims.

Red cells

These are used in the treatment of anaemia which cannot be medically corrected. Incidences include when rheumatoid arthritis or cancer is involved, when red cells break down in a newborn baby, or for sickle cell disease. They are also essential to replace lost red cells after accidents, surgery and after childbirth.

Platelets

Bone marrow failure, post transplant, chemotherapy treatments, and leukaemia.

:: Facts about blood

It was only discovered that blood came in different types in 1900 - the National Blood Service was set up 46 years later

Blood comes in four main types, O, A, B and AB. Group O is the most common. Blood can also be subdivided into its main components - red cells, white cells, platelets and plasma

Blood groups are different in different countries. Almost all South American Indians are group O, while about 25 per cent of Asians are group B. In Norway, most people are group A

The best place to find group O blood is in the north of England

The south of England has a greater proportion of group A blood donations

Last year 2.1 million donations were collected from about 1.6 million donors - about five per cent of the population giving two or three times a year

You have about five billion red blood cells in every litre of blood

The first successful blood transfusion was carried out in 1665 by Dr Richard Lower, using animals as subjects.

When surgeons started performing transfusions on humans, initially with animal blood, they could not understand why their recipients kept dying.

It was not until 1900 when Dr Karl Landsteiner of Vienna discovered that blood comes in four different groups.

He got the Nobel Prize for his discovery. He died of a blood clot.

Updated: 11:22 Friday, January 06, 2006