Rachel Paine never meant to settle overseas but coming home risks death.

The former Lynfield College student was in her early 20s and living with a friend in Perth when she started getting dizzy spells. She couldn't get through a quarter of netball without feeling like she'd pass out.

After being hospitalised with a sharp pain in her stomach specialists eventually diagnosed an extremely rare blood and immune condition, called paroxysmal nocturnal haemoglobinuria (PNH).

In simple terms, some of Paine's blood cells were missing a protein and her immune system was attacking them as a result.

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That makes her anaemic - meaning she is constantly fatigued - and at a higher risk of potentially fatal blood clots.

Doctors arranged for her to go on a drug called eculizumab (marketed as Soliris), at the time one of the most expensive in the world. Given through an IV transfusion every two weeks, the drug drastically cuts the risk of blood clots and reduces complications, prolonging survival.

The problem: eculizumab isn't funded in New Zealand, and costs about $600,000 per person, per year.

"[Doctors said] 'if you ever want to go back to New Zealand you are not going to have access to this drug'. And that started a whole different ball game with where my life was going."

With only her friend's family for support in Perth and getting sicker, Paine decided to return home anyway.

"I reached a point where I said, 'I can't do this, I'm living by myself, essentially trying to look after myself'. And I couldn't do basic things."

However, two weeks before her flight home - and before she'd started on eculizumab - Paine ended up in hospital with blood clots throughout her liver, and later in her lung.

"After that point they said, 'You go home and it's a bit of a death sentence'. I would have been 24 at the time. An eight hour flight from New Zealand."

New Zealand's drug-buying agency Pharmac referred the Herald to a statement it made in 2013 declining a funding application for eculizumab. The statement said the price - then about $670,000 per patient per year - sought by Alexion Pharmaceuticals was "extreme", and higher than in other countries.

"Eculizumab could benefit up to 20 people, at a cost of approximately $10 million per year. If funding was committed to the drug, it would mean potentially tens of thousands of New Zealanders missing out on new medicines which offer more health gain overall," Pharmac said at the time.

Dr Collette Bromhead, chief executive of the NZ Organisation for Rare Disorders, told the Herald it was tough to get medicines funded for patients with rare disorders such as PNH.

"New Zealand is slipping further and further behind other countries for access to medicines."

Some Kiwi patients had been given eculizumab at no charge by Alexion, but Paine was unable to get such compassionate assistance. As such, treatment in New Zealand would likely be much less effective blood thinners and transfusions.

She's able to return home for occasional holidays, with her drugs sent over from Australia so they can be given at Auckland City Hospital.

Last year Paine moved to Melbourne, to be closer to home and also because the city is a base for leading specialists. The move was extremely tough, with her low energy levels making it hard to work full-time and get out to make new friends.

Then she met her Australian partner, Tim, which "kind of changed everything".

"Now I have support and somebody there. And a base that I haven't had in a really long time. Which is pretty great."

The Herald met Paine and her parents John and Heather at their Lynfield home, during a short visit home - to introduce Tim, and help turn on the Christmas lights that make the home something of a local landmark.

Wednesday was Paine's 27th birthday. There are other drugs for her condition in the pipeline, which could be much cheaper and even more effective. Her hope is to regain normal energy levels, and to have the option to return permanently to New Zealand.

She is eternally grateful to have been diagnosed in Australia, a country she now feels less alone in and which has "allowed me to keep living, and live a reasonably normal life".

The Paines considered selling their home to help their daughter, but the cost would be ongoing. John Paine said he understood Pharmac had a limited budget, but the lack of support was still hard to accept.

"The toughest thing was knowing she was over there on her own," he said. "She's pretty strong getting through.

"We can't say, 'let's have a cup of coffee'...but we're more concerned about Rachel's happiness and health, and both of those boxes are more ticked now than they were a couple of years ago."

PNH (paroxysmal nocturnal haemoglobinuria)

• Blood and immune system disorder that affects about one in a million people.
• Leads to anaemia, severe stomach pain and potentially fatal blood clots, stroke, organ failure.
• A drug called eculizumab cuts the risk of blood clots and prolongs survival - but is needed life-long and costs upwards of half a million dollars a year, and isn't funded in NZ.
• New drugs are in development.