OBJECTIVE: The oral glucose tolerance test (OGTT) classifies subjects as normal, glucose intolerant or diabetic depending on glycemia at 120 min (T120) post-test. Five insulin profiles associated with different incidences of diabetes over 10 years\' follow-up were previously described following OGTT. However, insulin measurement is sensitive to hemolysis, and can be replaced by C-peptide assay on hemolyzed samples. However, little is known about patterns of C-peptide response to OGTT.
METHODS: In total, 128 patients were included, to establish preliminary baseline C-peptide values and to evaluate C-peptide response to OGTT in comparison to insulin response, using the Liaison XL immunoanalyzer.
RESULTS: Hundred patients had a normal glycemic response, 19 were classified as glucose intolerant and 9 as diabetic. In normal subjects, median C-peptide values (nmol/L, with 5-95 percentiles) were 0.53 (0.23-1.37) at baseline, peaking at 2.36 (0.94-1.83) at T60, and decreasing to 2.09 (1.13-4.36) at T120. The C-peptide response pattern was similar but flatter than the insulin pattern because of different catabolism pathways. Nevertheless, C-peptide and insulin response profiles were discordant in only 9.4% of cases. Profile 3 (C-peptide peaking at T60) was the most prevalent in normal patients whereas profile 4 (peak at 120 min and lower level at T30 than at T60) was the most prevalent in glucose intolerant and diabetic patients.
CONCLUSIONS: In OGTT, C-peptide could replace insulin determination on hemolyzed blood samples to predict the risk of type 2 diabetes.

OBJECTIVE: To compare: 1) 75 g oral glucose tolerance test (OGTT) and self-monitoring of blood glucose (SMBG) in identifying gestational diabetes mellitus (GDM) and other hyperglycemic statuses in pregnant women; 2) pregnancy outcomes according to glycemic status; and 3) participants\' opinions regarding both methods.
METHODS: A prospective study in women with a 50 g glucose load test ≥7.2 mmol/L at 24 to 28 weeks\' gestation and singleton pregnancy. Women underwent OGTT (blinded) at day 1, followed by 7 days of SMBG (4 daily measurements: fasting and 2 h postprandially) without modifying diet or lifestyle. GDM (OGTT+) was diagnosed using the criteria of the International Association of the Diabetes and Pregnancy Study Groups, while pregnancy hyperglycemia (SMBG+) was defined as ≥4/7 glucose values ≥5.3 after fasting or ≥6.7 mmol/L 2 h postprandially for any meal of the day. Equivalent management was provided to women with GDM and/or pregnancy-related hyperglycemia.
RESULTS: We divided 103 participants (age: 29.5±5.0 years; prepregnancy body mass index: 25.3±5.4 kg/m2) into 4 groups according to test results: OGTT+/SMBG+ (n=12, 11.7%); OGTT+/SMBG- (n=14, 13.6%); OGTT-/SMBG+ (n=9, 8.7%); and OGTT-/SMBG- (n=68, 66.0%). Clinical characteristics and maternal outcomes were statistically similar between groups. Neonatal complication rates were greater in groups with hyperglycemia than in the OGTT-/SMBG- group, notably neonatal hypoglycemia (9/12, 7/14, 5/9 vs. 6/68; p<0.001). Participants reported no convenience difference between methods but would prefer OGTT for a future pregnancy.
CONCLUSIONS: More than half of the women with OGTT+ were normoglycemic in daily life. Conversely, 11.7% of women with OGTT- had pregnancy hyperglycemia. OGTT+ and/or SMBG+ were equally associated with greater neonatal complications. This study suggests that alongside OGTT, SMBG could improve the care of pregnant women.