Undiagnosed diabetes in Wales has been described as a hidden epidemic by campaigners.
The type 2 form of the condition is the cause of most concern. It is affected by lifestyle, whereas type 1 is genetic. Type 2 diabetes, if left untreated, could lead to amputated limbs, blindness, kidney disease, heart attack and stroke.
Josh James from Diabetes UK Cymru said: "There are currently over 194,000 in Wales living with a diagnosis of diabetes.
"We estimate that 90% of those are type 2 - so that's around 175,000. We also estimate that there's about 61,000 people who have type 2 diabetes but haven't yet been diagnosed, which would put the total number of people in Wales with diabetes at over a quarter of a million, and it's growing.
"It is a hidden epidemic and a lot of the people out there aren't aware of how serious the condition is and they aren't aware of the risks and their own risk of developing it."
John Landon was undiagnosed for years until an experience on a work trip prompted him to see a doctor.
He said: "I had a tremendous thirst, you couldn't believe how thirsty I felt. Between here and Oxford I called in every service station to get a bottle of coke, regular coke, not diet coke. I keep a carrier bag in the car when I go away. When I come back I'd drunk 28 bottles of full strength coke."
GP Dr David Bailey, says John was essentially pouring fuel on the fire.