High blood glucose levels can lead to the formation of Ketones (poisonous chemicals) in the blood. Untreated, these chemicals become progressively more acidic - hence the term 'ketoacidosis' Ketones can lead to 'ketosis' or diabetic coma and it is therefore important to be aware that they may be present in your system from time to time and what to do about it if they are.
Ketoacidosis usually takes 24 hours to develop but can worsen unless you take action. The first signs are likely to be thirst, increased urination, tiredness, evidence of ketones in the urine and blood sugar levels above 15 mmol/l. It may be possible to bring things under control by taking extra short-acting insulin, but if there are moderate to large amounts of ketones in the urine and/or you are vomiting, feel drowsy or start breathing deeply, you need immediate medical assistance. Hospital treatment is sometimes necessary to stabilize the condition.
If you are ill, vomiting or your blood glucose level is high (15mmol/l or more) you should test your urine for ketones. You should have a supply of urine testing strips such as 'ketostix' - if you haven't - contact your GP and get some. (They can be added to your repeat prescription) If the test does prove positive, seek medical advice immediately.
Ketones smell like rotten apples or pear drops and may be detected on the breath. The over breathing is a result of the body trying to blow out the acid. Other symptoms include confusion, weakness, increased urination, excessive thirst, nausea, vomiting and abdominal upsets. This site also contains a section about coping with your diabetes during illness.