High levels of ketones are not a long term complication, they are an acute one
Since ketones are formed when fats are broken down. Some people who are dieting like to be 'in ketosis.' See Patch's posting. It is a very different matter if the ketones are produced because the cells haven't sufficient insulin to access the available glucose. They can build up very quickly making the blood acidic... diabetic ketoacidosis which can lead to a diabetic coma.
People who have frequent incidences of DKA, may also have higher than desired average blood glucose levels. Its these high averages or wildly fluctuating levels that over time, can lead to other complications.( ketones
may be dangerous during pregnancy though this is disputed by some)
I don't know if you wanted more on ketones, DKA and type 1 but this is quite a good article, its addressed to young people who pump, but most is applicable to all type 1s.
(nb American levels so divide by 18 ie 150mg = 8.3mmol)
http://www.netwellness.org/question.cfm/35485.htm
You should ask your doctor what to do if you have ketones present.(best to do it before you need the advice, you may never need it but its best to be prepared). You would need to take larger amounts of insulin than would be necessary just to bring blood glucose levels down. Drinking lots of fluids also helps.
When should you check for ketones? (my doctors protocol)
Anytime blood glucose is over 13.8mmol
When ill. Often illness, infections, or injuries increase the need for insulin and can cause sudden high blood glucose and this is an especially important time to check for ketones.
If planning to exercise and the blood glucose is over 13.8mmol.