This book gives the practitioner a practical approach for diagnosing blood sugar disorders. The tests recommended in this volume separate disorders of blood sugar into their four main types. These categories, in turn, dictate the appropriate medications which should be chosen for each. Patient case examples are provided. It is important to note that hyperglycemia does not define diabetes mellitus. Hyperglycemia may be constant, or may fellow hypoglycemia (the Somogyi phenomenon). Somogyi rebounds occur not only after excess use of hypoglycemic agents but also after hypoglycemia resulting from endogenous hyperinsulinemia (e.g. Nesidioblastosis, insulinoma) or defects in hypothalamic regulatory function. Evidence is presented for the existence of a disease of hypothalamic regulation, which results in spontaneous recurrent hypoglycemia. It is shown that this disorder along with Nesidioblastosis often produces white matter lesions on the non-contrast T2 Flair MRI. These lesions are commonly misdiagnosed as multiple sclerosis or ascribed to “small vessel disease”. In fact they can either be the result of severe hypoglycemia or hypoxia. The processes of recurrent hypoxia (e.g. from sleep apnea) or recurrent hypoglycemia are the likely causes of dementia. Diabetes mellitus is defined as due to impaired production or impaired release of insulin by the pancreas. In Nesidioblastosis the overproduction of insulin can be measured by a modified glucose tolerance test (with insulin levels added). Both these entities can present with hyperglycemia but are 180 degree opposites. Treating a Nesidioblastosis patient with insulin on the basis of a few elevated blood sugar measurements can result in severe injury or death of the patient. The same applies to a patient with rebound hyperglycemia (Hypothalamic Hypoglycemia). They may also present with several elevated blood sugar readings. Illustrative cases are presented in this book. The use of the nuclear ligands (TZD’s. GLP-1) in combination improves renal function. Cases are presented of this finding. Both pancreatic and cognitive function may be improved by these agent. HgbA1c testing should never be used to estimate the adequacy or appropriateness of treatment for a patient with a blood sugar disorder. Since it is simply an index to the three month average of blood sugars it cannot detect the most dangerous outcome of treatment or of the disease process, i.e. hypoglycemia. The homeostatic range of blood sugar for humans is 70 mg% to 140 mg%. In the healthy individual the blood glucose should never fall outside of these limits. If such a deviation is observed that patient is suffering from one of the four major diseases of blood sugar described in this book. The continuous glucose meter should be employed in all patients suspected of having a disorder of blood sugar. Since human blood sugar may fluctuate every 60 seconds even this monitor may miss clinically significant hypoglycemic events, as it only averages one minute blood sugars over five minutes. Many patients will experience hypoglycemia during sleep, and not wake. Continuous blood sugar monitoring is therefore indispensable. The notion of “insulin resistance” is fallacious. With the exception of those dying in infancy because of abnormally formed and dysfunctional insulin, no one develops resistance to insulin in later life. This mistaken viewpoint has prevented physicians from recognizing the injury to brain, pancreas and kidney caused by hypoglycemia.