She said hospitals need a regular supply of blood from donors to meet the needs of the number of patients who need transfusions each day.
About 40% of the donors donated regularly, or once every three to four months. The remaining 60% may donate once a year and many of them wrongly believed they should give only when an urgent demand for blood was publicly announced.
The blood centre had to find ways to motivate them to donate regularly, Dr Soisang said.
The centre urged young people to donate blood more often because they are generally more physically ready.
Rapee Noppakhun, a blood donor, aged about 40, said she wanted to donate because she "simply wanted to give and no further explanation is needed".
Mrs Rapee said she felt happy when giving blood even though she was too scared to look at the blood packs around her.
"I plan to give my blood until I'm 60, as donors should be people aged between 17 and 60 years old.
"I encourage everyone to donate blood because your blood can help prolong the lives of others," she said.
The National Blood Centre is organising a campaign at its head office on Henri Dunant Road from 8am to 4pm on July 14, which is World Blood Donation Day.
Blood donating campaigns will also be held at the National Blood Centre's provincial offices in Chiang Mai, Nakhon Sawan, Ubon Ratchathani, Khon Kaen, Nakhon Ratchasima, Chon Buri, Ratchaburi, Songkhla, Phuket and Prachuap Khiri Khan on Saturday.
For further information, please contact the National Blood Centre at 02-256-4300.