Objective: Retrospective analysis of oral glucose tolerance test (oGTT). The aim was to evaluate the influence of changed fasting glucose concentration on sensitivity and specificity of the detection oGTT results after 2 hours. Setting: Institute of Clinical Biochemistry, Internal Clinic, Faculty Hospital Ostrava; Department of Laboratory Methods, IKEM Praha; SEKK, Inc., Pardubice; Clinical Biochemistry Ward, Hospital Třinec-Sosna. Methods: Analysis of 977 oGTT results (75 g of glucose). Concentration of glucose was measured in capillary blood (according to practice before new recommendation of national societies). Three groups of oGTT results were defined as follows: „N“, i. e., glucose 2 hours post load under 7.8 mmol/l, „IGT“, i. e., glucose 2 hours post load between 7.8 and 11.09 mmol/l and „DM“, i. e., glucose 2 hours post load 11.1 mmol/l and higher. Absolute and relative frequencies of fasting glucose and post load glucose were evaluated. For oGTT results (N, IGT, and DM, respectively), sensitivities and specificities were calculated for different cut-off of fasting glucose. Results: There was significant number of increased post load glucose concentrations in patients with normal fasting glucose. Fasting glucose 5.0 mmol/l (capillary blood) was connected with sensitivity to detect IGT+DM of 77 % and specificity 60%; similarly for 5.5 mmol/l they were 65 and 78 %, respectively. Fasting glucose 5.0 mmol/l (capillary blood) was connected with sensitivity to detect DM of 89 % and specificity 60 %; similarly for 5.5 mmol/l they were 79 and 78 %, respectively. Conclusions: Decreased upper limit of fasting glucose is logically connected with increased sensitivity not only for diabetes mellitus, but also impaired glucose tolerance. The specificity is still acceptable. Selection of higher cut-off would be connected with decreased detection of patients requiring correct care. Decreased cut-off seems to be advisable step to better diagnostics and care of patients with impaired glucose tolerance and diabetes mellitus. On the other hand, the extent of changes in cut-off should be compared with many other factors. Authors recommend to evaluate data from oGTT with glucose concentration measured in venous plasma i.e., with respect to updated guidelines.

        Key words: diabetes mellitus, oral glucose tolerance test, sensitivity, specificity.