Aneurin Bevan University Health Board (ABUHB) has spent £18.9 million on agency and bank staff for registered nursing so far in the current financial year.
And a further £9.5m has been spent so far on bank and agency healthcare support workers.
The health board runs the likes of The Grange and Nevill Hall hospitals.
Sarah Simmonds, the health board’s executive director for workforce and organisational development, said ABUHB was taking new measures “to reduce our reliance on bank and agency [staff]”.
The figures were announced at the health board’s annual general meeting, after the health board reported ongoing financial pressures and overspends on running services.
Agency costs, along with rising bills for prescription drugs and energy, had contributed to a £36.3m overspend on running the health board’s services, Rob Holcombe, the executive director of finance, said at the meeting.
Caerphilly councillor Kevin Etheridge asked what the health board was doing to reduce its reliance on agency staff.
Ms Simmonds said work over the past 12 months had already started to show “some impact”.
“Primarily, we have focused on reducing agency in the first instance, and for our monthly average costs for this financial year our healthcare support worker agency costs have been around £240,000 compared to being over £880,000 [in the] last financial year,” she said.
“Our registered nursing agency costs have been around £1.4m per month, compared to last year an average of £1.8m a month.”
Ms Simmonds said the health board was reviewing its processes to make sure the health board was being “as efficient as possible with our deployment of the workforce”.
The organisation had also “worked hard to recruit and enlarge our healthcare support worker substantive workforce”, and had also been “recruiting overseas and locally for registered nursing”, she added.
Another priority for the health board was worker retention and “making sure we support the staff that we currently have to stay with us and develop”, Ms Simmonds said.
These aims were “underpinned” by the health board’s new “nursing workforce strategy”, which seeks to retain and develop staff by “widening access and creating more opportunities through nurse cadets, apprenticeships and flexible training”, Ms Simmonds added.