Skip to content

Glucose in Serum (Plasma)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of glucose (sugar) present in your blood drawn from a vein.

Quick summary

["A simple blood test to check your blood sugar levels."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
49689-3
Short code
GTT p 100 g Glc PO SerPl-Imp
Synonyms
GTT p 100 g Glc PO SerPl-Imp
Category
glucose
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
true
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your doctor may order this test to monitor blood sugar levels for conditions like diabetes, track glucose responses after meals, or evaluate metabolic health. It’s also used in emergency situations to assess shock, dehydration, or other life-threatening conditions.

What to Expect Before the Test

You may be asked to fast for 8–12 hours before the test if it’s part of a fasting glucose study. Otherwise, you can eat and drink normally. Avoid smoking or caffeine before the draw. Wear comfortable clothing and plan to sit quietly for a few minutes afterward as you may feel lightheaded.

During the Test

A healthcare provider will insert a small needle into a vein in your arm to draw blood. You may feel a brief pinch, but it usually doesn’t cause discomfort. The blood sample is sent to a lab for analysis.

After the Test

You can resume normal activities immediately. Apply gentle pressure to the site to stop any bleeding. If you experience dizziness, nausea, or excessive bruising, contact your provider.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Serum/Plasma Glucose

Frequently asked questions

What does a ‘glucose test’ measure?
It measures the concentration of glucose (sugar) in your blood, typically drawn from a vein. This helps assess how your body processes sugar and identifies potential diabetes or metabolic issues.
How long does it take to get results?
Results are usually available within 1–2 business days, depending on your lab’s processing time. Your doctor will discuss them with you during your follow-up visit.
Can I eat or drink before this test?
If fasting is required (e.g., for a fasting glucose test), follow your doctor’s instructions. Otherwise, you can eat and drink normally unless specified otherwise.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy