During a workplace screening programme in a manufacturing unit in Bangalore, 500 employees aged 30–60 years were screened for diabetes. Fasting blood glucose was measured in all, and 45 individuals had FBG ≥ 126 mg/dL. Which investigation is most appropriate to determine the true prevalence of diabetes in this population and avoid misclassification?

Explanation

## Epidemiological Approach to Diabetes Diagnosis and Avoiding Misclassification ### The Core Diagnostic Principle **Key Point:** According to WHO (2006) and ADA (2024) guidelines, a diagnosis of diabetes in an **asymptomatic individual** based on a single elevated fasting blood glucose (FBG ≥ 126 mg/dL) **must be confirmed by repeating the same test on a separate day** before a diagnosis is established. This is the standard approach to avoid misclassification due to transient elevations, pre-analytical errors, or biological day-to-day variability. ### Why Repeat FBG in the 45 Individuals is Correct | Criterion | Rationale | |---|---| | **WHO/ADA guideline** | Asymptomatic individuals require a second confirmatory test on a separate day | | **Avoids false positives** | Transient stress hyperglycaemia, acute illness, or lab error can cause a single spurious elevation | | **Same test repeated** | Confirmation is most reliable when the same test (FBG) is repeated, maintaining diagnostic consistency | | **Targeted to screen-positives** | Only the 45 with elevated FBG need confirmation — this is the standard two-step screening-diagnosis algorithm | **High-Yield:** The question asks specifically about avoiding **misclassification of the 45 screen-positive individuals**. The correct epidemiological and clinical approach is to repeat the FBG on a separate day in those 45 individuals, as mandated by WHO and ADA diagnostic criteria. ### Why Other Options Are Suboptimal 1. **OGTT in all 45 individuals (Option B):** - OGTT is a valid confirmatory test but is cumbersome, time-consuming, and not the first-line confirmatory step when FBG was the initial screening tool - WHO guidelines prefer repeating the same test (FBG) for confirmation in asymptomatic individuals 2. **HbA1c in all 500 individuals (Option C):** - HbA1c ≥ 6.5% is a valid diagnostic criterion (ADA 2010 onwards), but it is NOT the standard confirmatory step after an elevated FBG in a workplace screening programme - HbA1c can be falsely low in haemolytic anaemia, haemoglobinopathies (common in India), and falsely high in iron deficiency — reducing its reliability in population surveys without prior haematological screening - The question asks how to **confirm** the 45 screen-positives and avoid misclassification, not how to redesign the entire screening programme - Large Indian surveys (ICMR-INDIAB) do use HbA1c for prevalence estimation, but this is a different epidemiological context from a workplace confirmation exercise 3. **Random blood glucose in all 500 (Option D):** - Random blood glucose is highly variable and has no role in confirming diabetes in asymptomatic individuals - Increases, rather than reduces, misclassification ### Diagnostic Algorithm per WHO/ADA ``` Screen-positive (FBG ≥ 126 mg/dL, asymptomatic) ↓ Repeat FBG on a separate day ↓ FBG ≥ 126 mg/dL again → Confirmed Diabetes FBG < 126 mg/dL → No diabetes (transient elevation) ``` **Clinical Pearl:** WHO 2006 guidelines explicitly state: *"In the absence of symptoms of hyperglycaemia, a single abnormal test result is not sufficient for diagnosis; a second confirmatory test is required."* Repeating the FBG in the 45 screen-positive individuals is the most appropriate, guideline-concordant step to determine true prevalence and avoid misclassification. [cite: WHO Diagnostic Criteria for Diabetes Mellitus 2006; ADA Standards of Medical Care in Diabetes 2024; Harrison's Principles of Internal Medicine 21e Ch 397]