Diabetes and blood sugar tests measure glucose in your blood now (fasting or random) and on average over the past 2 to 3 months (HbA1c). Insulin and C-peptide show how your body is handling sugar.
Why is it done?
They screen for diabetes and prediabetes, and monitor treatment. Screening is recommended from age 35, or earlier with overweight, family history, PCOS or a history of diabetes in pregnancy.
How to prepare
Fasting glucose and insulin need 8 to 10 hours without food (water is fine). HbA1c and random glucose need no fasting.
How to read your results
Fasting glucose of 100 to 125 mg/dL (5.6 to 6.9 mmol/L) or HbA1c of 5.7 to 6.4% means prediabetes. Fasting glucose of 126 mg/dL (7.0 mmol/L) or more, or HbA1c of 6.5% or more, means diabetes. High insulin with normal sugar points to insulin resistance.
Tests in this panel and their normal ranges
| Test | Normal range (adults) |
|---|---|
| Fasting Blood Glucose (FBS) | 70–99 mg/dL (3.9–5.5 mmol/L) |
| Random Blood Glucose (RBS) | 70–140 mg/dL (3.9–7.8 mmol/L) |
| HbA1c (Glycated Hemoglobin) | Below 5.7% (below 39 mmol/mol) |
| Fasting Insulin | 2–25 µIU/mL (12–150 pmol/L) |
| C-Peptide | 0.8–3.5 ng/mL (0.26–1.16 nmol/L) |
Ranges vary slightly between laboratories. The range printed on your own report is the one to go by.
Last updated
This page is for general education and is not a diagnosis. Normal ranges differ between laboratories, so always compare your result with the reference range printed on your own report, and discuss abnormal results with your doctor.