Glucose, Blood, Mass Concentration (Serum or Plasma)

Why It’s Done

Doctors order glucose tests to diagnose or monitor conditions such as diabetes, hypoglycemia (low blood sugar), or other metabolic disorders. It may also be used during pregnancy, before surgeries, or to evaluate symptoms like excessive thirst, frequent urination, or unexplained weight changes.

Sample Collection and Preparation

Blood is collected via a vein (usually in the arm) or from a small cut in a finger. The sample is processed into either serum (after clotting) or plasma (using an anticoagulant), then sent to a lab for analysis. Glucose levels can also be measured in urine or saliva in some settings.

How the Test Works

The test uses an enzymatic method to detect glucose. Enzymes react with glucose, producing a measurable change that the lab analyzes to determine the concentration. This method is highly accurate and widely used in clinical labs.

What to Expect Before the Test

For a blood draw, avoid eating or drinking (except water) for at least 8–12 hours before testing to get an accurate fasting glucose level. If testing is for non-fasting purposes, inform your provider about recent meals or medications that might affect results.