General practitioners have been advised about the situation in a newsletter which advises patients sent on routine referrals will not be able to be seen and will be returned to the referrer.
The service will continue to see new patients with malignant blood conditions such as myeloma and leukaemia, but patients with lymphoma will be referred to oncologists.
Service clinical leader Dr Blair McLaren and manager Gary Reed advised the doctors they understood the substantial reduction in the service, which they hoped would be temporary, was likely to cause some anxiety for affected patients.
"However, in order to maintain a safe service at all, these changes are required."
The Southern District Health Board's Dunedin-based chief operating officer, Vivian Blake, said the departures of the two haematologists were not related. One of the specialists was on maternity leave.
The difficulty the service faced was that there was a "dearth of haematologists" and vacant positions were hard to fill.
The board was seeking the help of other district health boards, had assigned an extra registrar to the service to help and was also looking for locums.
GPs were generally very understanding and supportive when such events occurred and knew that "we're all in this together", she said.
In the newsletter, the service advises that where diagnosis is uncertain, referrals should be made to other hospital services.
Haematologists at Southern Community Laboratories had advised they were happy to discuss abnormal blood test results and advise on additional tests, the newsletter says.
Only urgent calls can be taken by the Southern Blood and Cancer Service haematologist.
Non-urgent questions can be sent by fax, to be reviewed as time allows.
The reduced service will also affect patients requiring follow-up.
Those not receiving active treatment may be referred back to GPs' care and lists are being reviewed to determine those who might be appropriate for discharge.
GPs have been asked to do what they can to help reduce the volume of blood results coming in to the service by determining whether it is still necessary to send the information.
"We continue to receive copies of results of some patients who have previously been discharged from the service," the newsletter said.
