Type 1 diabetes mellitus diagnosis in young adult preceded by years of elevated postprandial and fasting glucose but normal HbA1c: A clinical example of discordance.

Herein, a case study of an individual with fasting blood glucose (FBG), glycosylated hemoglobin (HbA1c), and postprandial blood glucose (PBG) measures from the 3 years preceding their type 1 diabetes mellitus diagnosis is used to highlight discordance among these common diagnostic tests. Data from the patient's own records, participation in clinical research, and healthcare provider were collated. Measures of FBG (90-160 mg/dL) and PBG (195-247 mg/dL) were elevated for 3 years with a normal HbA1c (5.0-5.4%) and without any symptoms. Overt symptoms, including polyuria, polydipsia, and unexplained weight loss, manifested 3 years later prompting the patient to contact their physician. Testing revealed an elevated HbA1c (9.8%) and presence of glutamic acid decarboxylase autoantibodies (GAD) (9 IU/mL). Daily body composition measures and weighed food logs from the 3 months preceding and 4 months after diagnosis illustrate the effects of glucose spilling and inadequate insulin levels. Both FBG and PBG indicated diabetes 3 years prior to HbA1c. While FBG, PBG, and HbA1c are considered equally appropriate for screening and diagnosing diabetes, this case study highlights the need to revisit important distinctions between these tests that explain their frequent discordance.