The human body's blood sugar levels are tightly controlled by the hormone insulin, produced by the pancreas. If the pancreas produces too much insulin, then the blood sugar will fall to low levels (hypoglycaemia). Insulin overproduction can happen as a result of the body misreading a change in blood sugar levels after eating (such as after obesity surgery) or through tumours of the pancreas which overproduce insulin (insulinomas).

Hypoglycaemia can cause subtle symptoms such as tiredness, poor concentration, or dizziness and if untreated more severe symptoms including fits, coma and death. Low blood sugars can go unnoticed at night and if levels fall frequently, people can lose their ability to notice subtle symptoms.

People suspected of having hypoglycaemia require a series of investigations to try and reproduce a low blood sugar under controlled conditions. This often requires an admission to hospital for a few days and multiple finger pricks to test the blood sugar - which patients often find painful. If low blood sugars caused by too much insulin are confirmed then medical treatment is started in the first instance, with surgery possibly following later. The only way to check whether these medications are working is by home fingerprick glucose measurements. If people have low sugars at night or have lost their ability to notice symptoms of low blood sugar, it is very difficult to be sure that the medical treatment is working.

The investigators plan to use continuous glucose monitoring probes to measure patient's blood sugar prior to and during admission for formal investigation for hypoglycaemia (alongside conventional fingerprick and blood testing). This might allow us to exclude hypoglycaemia as a cause of their symptoms, avoiding lengthy admissions.

The investigators will also use this technology (alongside fingerprick testing) to test how well medical treatment is working in patients with proven hypoglycaemia.