Planning permission has been granted to build a pathology building on the Truro site of Royal Cornwall Hospitals NHS Trust (RCHT).
It paves the way for bosses to demolish the old department to make way for a new hospital for women and children, the trust said.
Pathology departments support patient care through work such as blood tests.
Pending final NHS approval, work on the new pathology building is due to start in 2024.
Allister Grant, chief medical officer for RCHT, said: "This planning approval is a crucial step forward in our mission to deliver outstanding care for our patients across Cornwall and the Isles of Scilly.
"The advanced technologies and improved infrastructure of the new pathology building will not only enhance diagnostic precision but will also contribute to safer and more efficient healthcare delivery."
The trust said the planning permission marked a "significant milestone" for the new women and children's facility, due for completion by 2028.
Under the plan, the new pathology building will sit next to the current microbiology building and opposite the Trelawny Wing main entrance, the trust added.
It said the existing pathology laboratories and services would eventually be moved out of their location in the "Link Corridor", which will be demolished in 2026 to make way for the new Women and Children's Hospital.
RCHT's Pathology Department supports all parts of patient care including prevention, diagnosis and treatment for RCHT patients and across all GP surgeries and the Community Hospitals in Cornwall, the trust said.
The new "modern facility" would support "improvements in both the patient and staff experience", the trust said.
It would also encourage recruitment and retention of a "high-calibre workforce", it added.