Glucose, Plasma or Serum (Substance Concentration)

Why Is This Test Done?

Your healthcare provider may order this test to check for diabetes, high or low blood sugar, or to monitor conditions like kidney disease, liver problems, or metabolic disorders. It’s also used before surgeries or during pregnancy to ensure stable blood sugar levels.

What to Expect Before the Test

For blood tests, you may fast (not eat) for 8–12 hours before the draw, especially if checking fasting glucose. If you’re not fasting, your provider may specify otherwise. Avoid smoking or strenuous activity 30 minutes before the test. Tell your doctor about any medications or supplements you take, as they can affect results.

How the Test Is Performed

A healthcare professional will insert a small needle into your arm to draw blood. You may feel a slight pinch, but it usually doesn’t cause pain. The blood is then sent to a lab for analysis. Plasma or serum (liquid part of blood) is tested for glucose concentration using an enzymatic method.

What the Results Mean

Results are compared to general reference ranges, but your specific range may vary based on your health, age, and test context (e.g., fasting vs. random). High or low glucose levels may signal diabetes, prediabetes, or other metabolic issues. Your provider will discuss results in the context of your symptoms and medical history.