Hundreds of thousands of regular blood donors could be missing out on handy reminders to donate because their mobile phone numbers have not been recorded.
Australian Red Cross Blood Service spokeswoman Kathy Bowlen said many donors had been supplying blood for decades, before mobile phones became ubiquitous.
"With over half a million blood donors in Australia, many of whom have been donating for years, we know that our records are missing the mobile numbers for a couple of hundred-thousand donors," Ms Bowlen said.
She said some records had never had a mobile number listed while some donors might have switched numbers or providers without notifying the blood service.
Ms Bowlen urged regular donors who had not received a recent call or text message on their mobile from the blood service to call 13 14 95 and add the number to their details.
The blood service routinely texts donors to remind them of upcoming appointments.
Donated blood is crucial for cancer, road trauma victims, emergency surgery and renal dialysis patients, as well as burns victims.
One in three Australians will need blood in their lifetime but only one in 30 currently donates.