This randomized, crossover study evaluates the feasibility and accuracy of a self-administered oral glucose tolerance test (OGTT) at home using continuous glucose monitoring (CGM) compared to a standard clinic-based OGTT. Participants with prediabetes will undergo both home-based and clinic-based OGTTs, with glucose levels measured via CGM and venous plasma glucose. The primary outcome is the correlation between CGM-based glucose values and standard OGTT results. Secondary outcomes include diagnostic agreement, metabolic hormone associations, and feasibility of home-based testing as a diagnostic tool for dysglycemia.

This study aims to evaluate the feasibility, accuracy, and diagnostic utility of a self-administered oral glucose tolerance test (OGTT) at home using continuous glucose monitoring (CGM) compared to a standard clinic-based OGTT.

Study Design Type: Randomized, crossover study Participants: 75 adults with prediabetes Intervention: Each participant will complete both a home-based OGTT with CGM and a clinic-based OGTT with venous plasma glucose measurement.

Primary Objective To assess the correlation between glucose values obtained from a CGM-based home OGTT and a standard venous OGTT performed in the clinic.

Secondary Objectives Evaluate diagnostic agreement between CGM-derived and venous glucose measurements.

Assess variability in glucose responses between the two methods. Investigate associations between OGTT results and metabolic/sex hormones. Determine feasibility and patient adherence to home-based testing.

Methods Participants will be randomized into two groups: one starting with a clinic-based OGTT, the other with a home-based OGTT, followed by a crossover period. CGM will continuously monitor glucose responses, and standard venous plasma glucose measurements will serve as the reference method.

Clinical Relevance A validated home-based OGTT using CGM could improve access to glucose tolerance testing, reduce patient burden, and enhance early detection of dysglycemia.

Inclusion Criteria:

• Prediabetes indicated by ≥2 of the following values, measured at separate occasions or through different analyses during the past 2 years:
• - Fasting venous plasma glucose ≥6.1 but ≤6.9 mmol/L
• - Non-fasting venous plasma glucose ≥7.8 but ≤11.0 mmol/L
• - HbA1c ≥39 but ≤47 mmol/mol
• Access to a smart phone which is compatible with the CGM application and has working Bluetooth connectivity
• Ability to read and respond to online instructions and questionnaires in Swedish.

Exclusion Criteria:

• T2D indicated by ≥2 of the following values, measured at different occasions or through different analyses:
• - Fasting venous plasma glucose ≥7.0 mmol/L
• - Non-fasting venous plasma glucose value ≥11.1 mmol/L
• - HbA1c ≥48 mmol/mol
• Previous bariatric surgery e.g., gastric by-pass or gastric sleeve surgery
• Body mass index <20 kg/m2
• Body weight <43 kg
• Current pregnancy
• Need of regular use of GLP-1 receptor agonists, SGLT-2 inhibitors, acetaminophen or ascorbic acid supplements during the study period
• Fear of needle sticks
• Shift work during the study period
• Involvement in the study design, data collection, analysis, or participant recruitment.

If suitable according to ethical guidelines.