David Mulligan says he was finally allowed to take insulin more than seven hours after arriving at Kirkcaldy police station in Fife.
He said police had not learned their lesson following the case of Sheku Bayoh, whose death after being restrained by officers in Kirkcaldy is under investigation by the Police Investigations and Review Commissioner.
“At all times they knew I needed medical assistance and was denied it,” said Mr Mulligan who previously had part of his foot amputated because of complications from type one diabetes.
The 39-year-old from Glenrothes said an officer would be visiting him in the coming days to take a formal complaint.
Police Scotland confirmed it was taking the matter extremely seriously.
Mr Mulligan was detained last week after becoming involved in an argument over his son’s scooter.
He said his blood sugar levels were taken an hour after he was taken into custody and showed a reading of 24 millimoles per litre.
However, he said his syringe for administering insulin had been confiscated.
According to Diabetes UK, high blood sugar, or hyperglycaemia, is anything above 8.5mmol/L two hours after a meal.
“They read 24, which is dangerously high and I told him I would need insulin and food urgently,” he continued.
“Hyperglycaemia affects moods and rational thought, and left untreated can cause a diabetic coma.”
In addition to high blood sugar, Mr Mulligan claims he had wounds which were bleeding.
He added: “After about two hours I was taken to see a nurse, but then pulled out for questioning, so still not having been treated for hyperglycaemia or the bleeding wounds I had.
“I was read my rights and questioned while still not mentally fit. I asked again for insulin and food, and was told this would come.
“After seven hours of being detained I was finally allowed to give myself insulin.”
He added: “This needs to stop and if it ultimately causes a change to take place that prevents this from happening to anyone else then as a community we have done our bit.”
A spokesman for Police Scotland: “At present, no complaint has been made to Police Scotland in relation to this matter however we have been made aware of the allegations published on social media.
“We are making efforts to engage with the male to ascertain the full details.
“We strive to provide the highest standard of service to the public and any reports contrary to this are taken extremely seriously.”