It's just a little prick but it can be the difference between life and death.
One small donation of blood could save the lives of up to three people. But the sight of needles and the red sticky stuff is too much for some people to bear.
Only 3.6 per cent of the New Zealanders eligible to donate blood do so and of those only 2 per cent are Polynesian and 6.6 per cent Maori.
Mangere's Neighbourhood Policing Teams have put their own bodies on the line to highlight the need for blood from people in those communities.
Tongan Constable Pat Mofoakifolau says once he realised there was a big demand for blood to help his people he was happy to give in an effort to encourage others.
"It's about the groups that aren't donating. There's very little awareness out there in the community that we can help our own people by just doing simple things like donating blood."
Mangere police showed up in force to roll up their sleeves but even some of the most hardened coppers were squeamish when it came to their turn.
Samoan Constable Jamie Tavake-Tovi was "really nervous" when he lay back in his chair. He couldn't look at the needle as the New Zealand Blood Service nurse eased it into his vein.
"It's ironic because my family are all working in hospitals with needles."
But after his initial apprehension Mr Tavake-Tovi reckons it wasn't as bad as he thought it was going to be. He just looked away during the short time it took to give his donation.
Constable Anne Napara was terrified. The Cook Islander says she had to be talked into donating.
"But it's for a good purpose. I know it's to save people's lives so that's why I've put my fears aside."
At the end of the procedure she was glad she did it and proud of herself for overcoming her fears. Her arm was a little bit sore at the start but it was nowhere near as bad as she thought it would be, she says.
- © Fairfax NZ News