| Test Name | Full Form / Description | What It Measures | Purpose / Use | Helps Diagnose / Differentiate | Typical Interpretation |
| HbA1c | Glycated Hemoglobin | The percentage of glucose attached to red blood cells | Shows average blood glucose control over the past 2–3 months | Used to diagnose diabetes and monitor long-term glucose control | • Normal: <5.7% • Prediabetes: 5.7–6.4% • Diabetes: ≥6.5% |
| OGTT | Oral Glucose Tolerance Test | How the body processes glucose after a sugar load | Measures glucose levels before and 2 hrs after consuming 75 g glucose | Used to diagnose prediabetes and diabetes (especially gestational) | • Normal: <140 mg/dL (2 hr) • Prediabetes: 140–199 mg/dL • Diabetes: ≥200 mg/dL |
| Insulin | Hormone secreted by pancreas | Level of insulin in the blood | Evaluates insulin resistance or deficiency | Helps assess type 2 diabetes, insulin resistance, or insulinoma | • High: Insulin resistance / insulinoma • Low: Insulin deficiency (T1DM) |
| C-peptide | Connecting peptide (released with insulin) | Reflects body’s own insulin production | Determines whether insulin is produced endogenously or from injections | Differentiates type 1 vs. type 2 diabetes and evaluates pancreatic function | • Low: Pancreas not producing insulin (T1DM) • Normal/high: Insulin resistance (T2DM) |
| GAD65 Antibodies | Glutamic Acid Decarboxylase-65 Autoantibodies | Presence of antibodies attacking pancreatic beta cells | Detects autoimmune activity against insulin-producing cells | Confirms autoimmune (type 1) diabetes or LADA (latent autoimmune diabetes in adults) | • Positive: Autoimmune destruction of beta cells • Negative: Suggests non-autoimmune (T2DM) cause |
HbA1c and OGTT> → Indicate how well blood glucose is controlled and confirm diabetes diagnosis.
Insulin and C-peptide → Show how much insulin the body is producing and whether it’s internal or injected.
GAD65 antibodies → Reveal if the immune system is destroying pancreatic cells (type 1 diabetes).
High GAD65 + Low C-peptide → Type 1 diabetes (autoimmune).
Normal GAD65 + High Insulin/C-peptide → Type 2 diabetes (insulin resistance).
