The purpose of this study is to measure how often low blood sugars occur in people who live with both adrenal insufficiency (AI) and diabetes and need to take insulin. People who live with AI need to take steroid replacement tablets every day, for life. Two of the most common types of steroid replacement tablets are called prednisolone and hydrocortisone.

Low blood sugar (hypoglycemia) is a very common side effect of taking insulin and can often be unpleasant, frightening and dangerous. People who have adrenal failure are also at risk of hypoglycaemia, although this is rare. It is not known whether taking steroids affects how often hypoglycaemia happens.

The study has three aims:

1. To measure how often low blood sugars occur at night in people who live with with both adrenal insufficiency (AI) and insulin-treated diabetes
2. To compare how often low blood sugars occur in people taking prednisolone for their AI versus those taking hydrocortisone.
3. To compare the patterns throughout the day for low blood sugars in those taking prednisolone versus those taking hydrocortisone.

The study will compare this information with results in people who have AI without diabetes.

Participants will be given continuous glucose monitoring systems (Dexcom G6 devices) which are small wearable devices that measure glucose levels throughout the day and night. They will be asked to wear a device for 30 days. Participants will not be asked to make any changes to their usual medications or their diet.

PURPOSE OF THE STUDY

The purpose of this study is to measure how often hypoglycaemia occurs in people who take steroid tablets for adrenal insufficiency and insulin for diabetes compared to individuals with adrenal insufficiency on steroid tablets without diabetes. To do this, participants will be given a continuous glucose monitoring (CGM) system, which is an effective and accurate way of measuring blood sugars throughout the day and night. This study will assess how often hypoglycaemia occurs, especially at night, and whether the type of steroid tablet people take affects how often hypoglycaemia happens.

STUDY AIMS

1. To measure how often low blood sugars occur at night in people with both AI and insulin-treated diabetes using CGM, and in people without diabetes who are matched in age, sex and steroid replacement (hydrocortisone or prednisolone).
2. To compare the frequency of low blood sugars in people taking prednisolone for their AI versus those taking hydrocortisone.
3. To compare the patterns throughout the day for low blood sugars in those taking prednisolone versus those taking hydrocortisone.

STUDY DESIGN

This study will observe 16 adults with both insulin-treated diabetes and adrenal insufficiency and 16 adults without diabetes who are matched for age, sex and steroid replacement. The investigators will aim to recruit 32 participants in total. Participants will spend 30 days in the study.

RECRUITMENT Recruitment will be undertaken in endocrinology and diabetes clinics at Imperial College Healthcare NHS Trust. Participant information sheets will be given to potential participants and following any questions, informed consent will be taken.

Participants will be given as much time as they require (at least 24 hours) to decide whether or not to take part - this can vary on a per participant basis.

Inclusion Criteria:

for test group:

• Confirmed diagnoses of adrenal insufficiency and insulin-treated diabetes for more than one year.
• Adults aged above 18 years

for matched control group:

• Diabetes mellitus excluded on baseline blood review
• Adults aged above 18 years

Exclusion Criteria:

• Measured eGFR ≤ 30
• Acute illness
• Abnormal thyroid function
• Admission to hospital
• Pregnant or planning pregnancy
• Breastfeeding
• Enrolled in other clinical trials, except at the discretion of the chief investigator
• Have active malignancy or under investigation for malignancy
• Severe visual impairment
• Reduced manual dexterity
• Unable to participate due to other factors, as assessed by the Chief Investigators

Adults living with insulin-treated diabetes and adrenal insufficiency.