The diagnosis of HI is based on history, physical exam and lab testing, and may also include genetic testing and special radiologic testing to distinguish between focal and diffuse. The following is a list of current methods for diagnosing the various types of HI.
The history of the child is an important piece of the puzzle. This includes information such as when the low blood sugars started, the timing of the low blood sugar and whether the hypoglycemia responds to diazoxide.
Based on obtaining samples at the time of a low blood glucose, these include insulin and other lab tests. In addition to an increased insulin level, other findings include low levels of blood ketones and fatty acids, and an inappropriately large response to an injection of glucagon.
Unfortunately, traditional methods of identifying a tumor or focus of cells, such as CT scan, MRI, and ultrasound, have not been successful in identifying Focal KATP HI. A research test to image focal lesions is being evaluated at CHOP: the 18F-DOPA PET scan. This uses a radioactive drug, 18F-DOPA, that is injected intravenously and concentrates in insulin cells for detection in a PET scanner (positron emission tomography). 18F-DOPA is not yet FDA approved, so the test is being done under a research protocol.
The pathology of the pancreas can be used to differentiate between normal pancreas tissue and hyperinsulinism tissue. Pathology refers to the study of tissue and cells under a microscope. During and after surgery, pathologists can identify whether the pancreas has areas of normal tissue and areas of hyperinsulinism tissue, or whether the entire pancreas has hyperinsulinism tissue. This information assists in the diagnosis of Focal KATP HI versus Diffuse KATP HI.
The DNA from a blood sample from the child and each parent can be analyzed for the mutations that cause the four most common types of HI. This process can take two weeks or longer. The results usually take too long to obtain to assist in immediate decisions about treatment. However, the information can confirm the specific type of HI and inform families about the risk of the same mutation occurring in future children. It is important to remember there are children with HI who have had no mutation found. It is likely that there are additional mutations which cause HI that have not yet been identified.
Genetic mutation analysis is for the four most common is available through several commercial laboratories.