Over the past few years, Elizabeth's father needed blood transfusions regularly to manage myeloma, blood cancer. Before he died last month, he was receiving up to two units of blood every week.

"We decided we would put deposits back into the blood bank because we were making quite significant withdrawals," Mr Taarnby said.

"After seeing the impact on a family member, and with the ability to have the same impact on other people, we couldn't look at each other and say we're going to be selfish and not do it anymore. Even though dad passed away last month, we will still continue to do it," he said.

The Red Cross Blood Service is experiencing a shortage of donors which could become critical if appointments are not filled.

In Canberra, 50 people or more need to put up their hand to donate in the coming week, to help fill the places of those sick with colds or flu.

The critical call out is for people with O-type blood groups.

Mr Taarnby is one of very few people with the blood type of O-negative. His donations can be used universally - anyone in an emergency situation.

Mrs Taarnby is blood type O-positive. Her blood is the most common, and therefore the most needed.

The Taarnbys have been donating blood for about two years now.

For the first time on Friday, Mr Taarnby was asked to donate platelets and plasma, rather than whole blood.

"My one donation of platelets is worth the equivalent of eight whole blood units, because of my O-negative they can combine it with other products," Mr Taarnby said.

"That pays back a lot from what dad had over the last couple of years, so I'll probably do that a few more times," he said.

Canberra Red Cross Blood Service community relations officer Sally Gavin said it was important people realised it could be them or their family member who needs blood next.

"You never know, it might be somebody you love," Ms Gavin said.

She said the Taarnbys story of wanting to give back was a great response.

"They have become very regular donors and for them it is because they want to give back.

"It's nice to know they respect that others were there for their family, and now they're donating to be there for others."

Critical days in the next two weeks for appointments to be filled are Wednesday and Thursday at the mobile unit at Brindabella Business Park, Friday June 2 at the mobile unit at Fairbairn and the Canberra Donor Centre, and Saturday June 3 at the donor centre.

Visit www.donateblood.com.au to find out more or book an appointment.