A 42-year-old man from rural India attends a health camp for screening. He is asymptomatic with no prior history of diabetes. His fasting blood glucose is 118 mg/dL. Which investigation is most appropriate to confirm or exclude diabetes in this individual?

Explanation

## Diagnostic Approach to Impaired Fasting Glucose **Key Point:** When fasting blood glucose (FBG) falls in the impaired fasting glucose (IFG) range (100–125 mg/dL), OGTT is the gold standard confirmatory test to differentiate between normal glucose tolerance, impaired glucose tolerance, and diabetes. ### Why OGTT Is the Investigation of Choice The patient's FBG of 118 mg/dL falls in the IFG range, which requires further clarification: - **FBG alone is insufficient** because IFG can progress to diabetes or remain stable; OGTT provides prognostic information. - **OGTT measures 2-hour postprandial glucose** after a 75 g glucose load, which is more sensitive for detecting abnormal glucose metabolism in the IFG range. - **Diagnostic criteria by OGTT:** - Normal: 2-hour glucose < 140 mg/dL - Impaired glucose tolerance (IGT): 2-hour glucose 140–199 mg/dL - Diabetes: 2-hour glucose ≥ 200 mg/dL ### Comparison of Diagnostic Investigations | Investigation | Strengths | Limitations | When to Use | |---|---|---|---| | **Fasting Blood Glucose** | Quick, convenient, reproducible | Misses IGT; IFG requires confirmation | Initial screening | | **OGTT** | Gold standard for IFG; detects IGT; prognostic value | Time-consuming, requires patient preparation | Confirm IFG; diagnose IGT | | **HbA1c** | Reflects 3-month average; no fasting required; less variability | Less sensitive in early dysglycemia; not recommended for IFG confirmation | Diagnosis and monitoring in established diabetes | | **Random Blood Glucose** | No preparation needed | Non-specific; high variability | Symptomatic patients only | **High-Yield:** According to WHO and Indian guidelines (ICMR-INDIAB), OGTT is mandatory when FBG is 100–125 mg/dL to determine true glycemic status and cardiovascular risk. **Clinical Pearl:** Approximately 25–30% of individuals with IFG progress to diabetes within 5 years; OGTT helps stratify this risk by detecting concurrent IGT, which carries higher progression risk than isolated IFG. **Mnemonic: IFG-OGTT** — *Impaired Fasting Glucose requires Oral Glucose Tolerance Test*