The test evaluates how efficiently the body clears glucose from the bloodstream.

Procedure:

Patient fasts for 8–12 hours.

A fasting blood glucose sample is collected.

Patient consumes a 75 g oral glucose solution (100 g for pregnant women).

Blood glucose levels are measured at intervals (commonly 1, 2, and sometimes 3 hours).

Clinical uses include:

Diagnosing type 2 diabetes mellitus.

Screening for gestational diabetes mellitus (GDM).

Detecting prediabetes (impaired glucose tolerance).

Investigating reactive hypoglycemia.

Often combined with Fasting Blood Sugar (FBS) and HbA1c for comprehensive evaluation.

Analyte: Blood glucose concentration at fasting and timed intervals after glucose load.

Normal Range (WHO criteria):

Fasting: < 100 mg/dL → Normal

2 hours post‑glucose: < 140 mg/dL → Normal

Abnormal Findings:

2 hours: 140–199 mg/dL → Impaired glucose tolerance (Prediabetes)

2 hours: ≥ 200 mg/dL → Diabetes mellitus

Clinical Use:

Provides a dynamic assessment of glucose metabolism.

Helps confirm diagnosis when fasting glucose or HbA1c results are borderline.

Essential for gestational diabetes screening.