Biomarker: Glucose, blood

Overview

Blood glucose is the concentration of glucose (sugar) in the blood, the primary fuel for cellular energy and a key regulator of metabolism.
Blood glucose levels reflect the balance between dietary intake, insulin secretion, insulin action, and hepatic glucose production, and are central to the diagnosis and management of diabetes and prediabetes.
High blood glucose (hyperglycemia) is commonly associated with diabetes and prediabetes, while low blood glucose (hypoglycemia) can result from diabetes treatment, certain medications, or other medical conditions.
Clinically, blood glucose testing is widely used to screen for and diagnose diabetes, evaluate symptoms of high or low blood sugar, and monitor ongoing treatment and disease control.

Clinical Use Cases

Screening for prediabetes and type 2 diabetes as part of routine health evaluations.
Diagnosing diabetes using fasting plasma glucose, random plasma glucose, and oral glucose tolerance tests.
Evaluating symptoms suggestive of hypo- or hyperglycemia, such as increased thirst, frequent urination, fatigue, shakiness, or confusion.
Monitoring blood glucose control in people with diabetes, including home capillary glucose testing and periodic lab-based measurements.
Adjusting diabetes medications (insulin and oral agents) and nutrition plans based on blood glucose patterns.
Assessing the impact of long-term medications that may affect blood glucose levels.
Supporting risk stratification and management decisions in individuals with prediabetes.

Specimen Types

Venous blood (plasma or serum), typically collected from a vein in the arm for laboratory testing.
Capillary whole blood from a fingerstick or other peripheral site for point-of-care or home glucose meters.

Measurement Methods

Laboratory venous plasma glucose measurement using automated chemistry analyzers.
Capillary blood glucose testing with handheld glucose meters and disposable test strips.
Oral glucose tolerance test (OGTT) with serial venous or capillary blood glucose measurements after ingestion of a standardized glucose load.
Continuous glucose monitoring (CGM) systems that estimate interstitial glucose and correlate closely with blood glucose patterns.

Test Preparation and Influencing Factors

Fasting requirements: For fasting plasma glucose and many OGTT protocols, no food or caloric drinks for at least 8 hours before testing; water is usually allowed.
Timing of collection: OGTT involves baseline and follow-up samples (commonly at 1 and 2 hours) after drinking a glucose solution; timing is critical for interpretation.
Recent meals: Non-fasting or random blood glucose values are influenced by timing and composition of recent food intake.
Medications: Insulin, many diabetes medications, and some non-diabetes drugs can raise or lower blood glucose and affect test results.
Acute illness, infection, stress, or surgery can raise blood glucose independent of usual patterns.
Physical activity: Recent vigorous exercise may lower blood glucose and alter results, especially in people using insulin or other glucose-lowering drugs.
Alcohol intake can affect glucose regulation and contribute to hypoglycemia or hyperglycemia in some contexts.
Improper fingerstick technique (unclean hands, inadequate blood drop, expired or improperly stored strips) can alter capillary glucose readings.