Definition

Measures the glucose level in the blood. Glucose is a type of sugar and the body's primary source of energy. The test checks whether the level is too high (hyperglycemia) or too low (hypoglycemia).

Purpose

Screening for prediabetes and diabetes in routine checkups. Investigating the cause of high/low blood sugar symptoms. Monitoring side effects of medications that affect blood sugar. Screening for gestational diabetes during weeks 24 to 28 of pregnancy. Monitoring the management of existing diabetes.

Results

Interpretation depends on which test was performed, other test results, and medical history. Higher than normal values may indicate diabetes risk; lower values may suggest other conditions.

Normal Values

Laboratory-specific, see the reference range on your report. For diagnostic thresholds, see the HbA1c entry.

Risks and Limitations

Fasting requirements vary by test:

  • Fasting blood glucose → at least 8 hours of fasting
  • Oral glucose tolerance test (OGTT) → fasting required
  • Random blood glucose and HbA1c → fasting not required

Dizziness may occur after the OGTT.

Related Tests

HbA1c (Glycated Hemoglobin)

Measures, as a percentage, how much of the hemoglobin in red blood cells is coated with glucose (sugar). Because red blood cells live for about three months, this test reflects

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OGTT (Oral Glucose Tolerance Test)

A test that shows how well the body moves sugar from the blood into the tissues. A fasting blood sample is drawn, a sugary liquid is given to drink, and a second blood sample

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Insulin (Fasting)

Insulin is a hormone produced by the pancreas that allows glucose in the blood to enter the cells for energy. The test measures the concentration of insulin in the blood.

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C-Peptide

C-peptide is an amino acid chain formed during the pancreas's production of insulin.

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Other related tests not yet in the glossary: Basic Metabolic Panel (BMP), Comprehensive Metabolic Panel (CMP), Continuous Glucose Monitoring (CGM).