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Diabetic Home Care and Monitoring (cont.)

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Tests for urinary ketones

Ketone testing is an important part of monitoring in type 1 diabetes. It is a tool that is often also used in pregnancies that are complicated by diabetes.

Ketones are formed when one fasts (for example, sleeping overnight) or when there is a profound lack of insulin. When the body produces an insufficient amount of insulin, the cells are unable to remove glucose from the blood, and the level of glucose in the blood rises. The cells respond to what appears to be a lack of glucose by stimulating the body to produce larger amounts of glucose. Rising blood glucose level causes more urination and dehydration. In addition, ketones are produced by the liver due to low insulin levels. The presence of ketones signals a condition in diabetics called ketoacidosis. Ketoacidosis signifies that the cells are not getting enough insulin.

Severe diabetic ketoacidosis is a medical emergency, since it can result in loss of consciousness and even death. There is a correlation between high blood glucose levels, dehydration, and ketones. The higher the glucose level, the more likely that ketones will be made. Therefore, patients with diabetes with blood glucose levels over 240 mg/dL should test promptly for urinary ketones. Patients with type 1 diabetes should test for ketones during any acute illness and during severe stress. Also, urinary ketones should be checked if any symptoms of ketoacidosis occur (such as nausea, vomiting, abdominal pain).

Ketones can normally be found in the urine. For example, after an overnight fast, ketones can be seen in up to 30% of people without diabetes. However, these levels of ketone production are usually below the threshold of measurement by the ketone test strips. The strips can also give false positive results when patients are on drugs such as captopril (Capoten). False-negative readings may be seen if the test strips are old, exposed to air, or if the urine is very acidic (such as after drinking a lot of orange juice, which is also high in vitamin C).

These tests are based on the color change that occurs when ketones react with sodium nitroprusside or similar compounds. The tests are performed in a manner similar to that of urinary glucose testing. Different tests detect the three types of ketones (acetoacetic acid, acetone, and ß-hydroxybutyric acid). For example, Acetest only detects acetoacetic acid and acetone, but not ß-hydroxybutyric acid. Ketostix detects only acetoacetic acid, which can produce false-negative results if only acetone and ß-hydroxybutyric acid are present in the urine. Ketone tests are supplied as strips or tablets.

The American Diabetes Association advises that ketone testing materials be available in the office setting and that physicians should prefer using blood ketone measurements over urine ketone measurements if possible. Home testing for blood ketones is also available, though not often used due to higher cost of the test strips.

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