Her Majesty Queen Sirikit has undergone medical tests and has "insufficient blood in the brain", the Royal Household Bureau said in a statement on her health.
"An x-ray showed that there is still a trace of a former illness of insufficient blood in the brain as per in 2012 but the check found no new abnormalities," the palace said in the statement.
Her Majesty went for a health check on Wednesday, it said.
The palace last released a statement on the Queen's health in 2014.