Early detection of (pre)diabetes, including impaired glucose tolerance is currently deficient because the best accepted standard, an oral glucose tolerance test (oGTT), is not feasible in a setting of screening or broad case-finding and other current methods lack in sensitivity. A previously reported study, and analysis of retrospective skin autofluorescence (AF) data, suggests that noninvasive skin AF may offer an alternative for detection of (pre)diabetes. The objective is to test the validity of a decision tree based on skin autofluorescence, and some simple clinical characteristics, as a detection tool for diabetes and impaired glucose tolerance. Sensitivity and specificity, positive and negative predictive value of this skin AF based decision model will be compared to those of fasting plasma glucose (FPG), glycated haemoglobin (HbA1c), and to two short questionnaires (Finnish Findrisk, and Cambridge score).

Study design: Skin AF, HbA1c and an oGTT (including an FPG) will be simultaneously performed in at least 120 persons with the characteristics described in the following paragraph. A Findrisk and Cambridge questionnaire will also be collected.

Inclusion Criteria: -age >20 years

• additionally a priori intermediate risk for IGT/diabetes: by having at least one criterion from the metabolic syndrome, or by at least once having had an increased glucose or glycated hemoglobin value in the preceding two years, but these outside the range of diabetes/IGT

Exclusion Criteria:-known diabetes mellitus

• use of oral antidiabetics for other purposes than diabetes such as hepatic steatosis
• local skin disease of the lower arm obviating skin autofluorescence measurement
• known serious renal insufficiency (s-creatinine > 180 umol/l).
• inability to fill in questionnaires

Subjects identified from an outpatient (vascular, lipid) hospital-based group, with an intermediate risk of (pre)diabetes, as defined by an age >35 years, and additionally at least one criterion from the metabolic syndrome, or at least once an increased glucose or HbA1c value in the preceding two years, but these outside the range of diabetes/IGT