BBC News health reporter
Once a month David Dokelman visits a clinic, rolls up his sleeve and remembers his dearly-loved son.
Andrew Dokelman was just eight when he became ill with a very aggressive cancer of the soft tissue and needed regular blood transfusions.
Andrew lost his batte with cancer but the generosity of others inspired his father to become a donor.
"Andrew was receiving platelets and I wondered where they came from," he said.
"I thought they were made, but then I realised people were donating them - that is why I have been donating since then."
Platelets are tiny fragments of bone marrow cells which circulate in the blood, clumping together to form clots which prevent bleeding following injury.
Platelet transfusions are often a vital part of treatment for many premature babies who can be highly susceptible to brain haemorrhages. Transfusions of just two or three teaspoons can cut their risk of dying.
Platelets are also given to patients whose bone marrow is not working properly.
They include unborn children who need transfusions in the womb and patients with cancer or leukaemia undergoing chemotherapy.
Since February 2002 David, from London, has made a total of 287 donations.
"I am just hoping I am helping other people," he said.
"People were kind enough to help my son when he was ill. I wish more people donated.
"I just want to go out and shout to people about donating.
"Because I am an old git it takes me an hour and 10 minutes to donate, but when I was a bit younger it took under an hour. It doesn't hurt at all."
Demand for platelets is rising and is up by 3% so far this year.
Supplies are particularly needed over the Christmas and New Year period, when donations are down and as platelets only have a five day shelf-life, the National Blood Service (NBS) is desperate for more donors.
Platelets can be donated more frequently than whole blood because no red cells are taken, so iron levels are not affected.
But not everybody who is a blood donor can give platelets.
Men often make more suitable donors as they have a larger volume of blood and generally bigger veins - of current blood donors about 50% of males would be suitable to donate platelets and about 20-25% of females.
During the process donors are linked to a machine which takes their blood and separates the platelets. These are collected while the rest of the blood is returned to the donor.
One donation collected by this method can provide two or three therapeutic platelet doses.
Platelet donors are encouraged to donate regularly, on average ten times a year.
They must be aged between 18 and 60, and have given at least one donation of whole blood.
Over the years David has probably helped save the lives of countless people he has never met - people like 20 month old Ayanna.
When Ayanna, from Croydon, was born at just 23 weeks last March she was tiny and weighed just 1lb 6oz (0.6kg).
She was very ill and in special care for four months. She was on a ventilator for five weeks and needed oxygen for nearly a year.
She was kept alive by regular transfusions and her mother Louise Abbott is grateful for the donations.
"She would not be here today if she did not have others' blood.
"It is essential especially for little ones to have the platelets.
"She needed so many transfusions. At the beginning she was having blood transfusions every couple of days and it seemed normal to see her having one.
"She had chronic lung disease and grade four bleeding in the brain.
"She is good now though. She has developmental delays and has problems with her left side and still has problems with the bleeding in her brain and we are not sure how that will affect her.
"But the blood definitely saved her life."
Dr Sheila MacLennan, Clinical Director, NHS Blood and Transplant, said that over the Christmas and New Year period stocks are desperately needed, particularly of platelets, which have a short life.
"Platelets are a very small blood cell but are a very vital blood cell as they are used for very sick patients. They play a vital part in helping blood to clot.
"The platelets only last five day. Over bank holidays we do have extra sessions, but they do take out the production capacity, and we don't run all the sessions we would.
"So we really need to remind donors to continue to replenish our stock because the patients don't stop needing them because it is a bank holiday."