This clinical study has been launched to collect spectral Raman data and reference measurements to establish and validate a calibration model for the device during daily glycemic fluctuations and evaluate analytical performance of device in the hypoglycemic range. The study is a combined home-based and in-clinic study where subjects will attend the clinic two times.

Inclusion Criteria:

• Male and female subjects between 18 and 40 years of age.
• Diagnosed with type 1 diabetes mellitus.
• Uses an insulin pen or pump.
• Hb1Ac > 55 mmol/mol at baseline visit.
• Skin phototype 1-4 according to Fitzpatrick skin tone scale.
• Willing to perform a minimum of 8 finger sticks per day during the study for the home-based study and approximately 16 finger sticks for the in-clinic study days.
• Willing to have a peripheral venous catheter inserted.
• Willing to provide written signed and dated informed consent.

Exclusion Criteria:

• Breastfeeding, pregnant, attempting to conceive or not willing and able to practice birth control according to approved contraceptives from NCA during the study execution (applicable to female subjects only).
• Subjects not able to understand and read Danish.
• Inability to comply with the study procedures as described by the study protocol, according to the opinion of the investigator.
• Subject is not able to hold hand/arm steadily (including tremors and Parkinson's Disease).
• Reduced circulation in hand. "Allen's test" is used for assessing hand circulation to evaluate occurrence of reduced blood.
• Extensive skin changes, tattoos or diseases on probe application site (thenar) that could interfere with the accuracy of the interstitial glucose measurements.
• Known allergy to medical grade alcohol.
• Having active cancer treatment and/or use tetracyclines and other medication / topical agents known to increase photosensitivity in skin.
• Medical history or any condition that may, in the opinion of the Investigator, compromise the subject's ability to participate
• Concomitant medical condition which could present a risk to the safety or welfare of the subject or study staff.
• Diagnosed with cardiovascular diseases.
• Subjects currently enrolled in another study.
• Radiotherapy for the past six months.