It will house biochemistry, haematology, blood transfusion and mortuary services.
This is the next step in the £842 million project to build Scotland’s biggest hospital and will create a 1,109-bed adult facility sitting alongside a 256-bed children’s hospital.
It will provide maternity, paediatric and acute services on a single site and should be completed by January 2015.
The laboratory will link to the main hospital via a subterranean tunnel.
Health secretary and Govan MSP Nicola Sturgeon performed a topping-out ceremony at the completion of the lab.
She said: “This is Scotland’s biggest-ever hospital building project and will be entirely publicly funded.
“This major investment shows despite the significant cuts to Scotland’s capital budget the Scottish government is continuing to prioritise spending on our NHS to improve patient care.
“Completion of the lab building is just the first step in this exciting journey for patients across the west of Scotland.
“Centralising services for all ages on a single site will ensure that everyone can access the widest-possible range of specialist services and will also bring with it increased efficiency, shorter waiting times and better continuity of care”.
Robert Calderwood, NHS Greater Glasgow and Clyde chief executive, was delighted with the “major strides forward” in healthcare following the completion of work on the lab.
He said: “The full project will see us complete a programme of investment of more than £1.5 billion in modern healthcare accommodation across both acute and mental health facilities.
“Taken together these major strides forward, with the new South Glasgow Hospital at the centre, (and) we will have the tools for the delivery of sustainable, high quality, cost effective healthcare for NHSGGC residents and beyond”.
The work was carried out by Brookfield Construction UK Ltd.
Project director Mike Sharples said: “We are very pleased to have reached this significant stage of the building works on the labs building to programme.
“Internal fit-out is progressing well and the first phase of the project is on course for completion in spring 2012 as planned”.