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Glucose, Serum

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

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

Quick summary

["Glucose levels help monitor blood sugar, especially for diabetes management."]

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

Key facts at a glance

LOINC
47859-4
Short code
Glucose 5M p Glc SerPl-sCnc
Synonyms
Glucose 5M p Glc SerPl-sCnc
Category
glucose
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
70
Ref high
100
Critical range
50 N/A – 400 N/A
Fasting
true
Population
adult
Sex
all
Age range
18–65 years
CPT
82947
SNOMED
260395008
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 Is This Test Done?

Your healthcare provider may order this test to check for diabetes, monitor blood sugar levels, diagnose conditions like hypoglycemia (low blood sugar), or assess how well medications are working. It can also help evaluate metabolic health or detect signs of kidney or liver issues.

What to Expect Before the Test

You may be asked to fast (not eat or drink) for 8–12 hours before the test, especially if it’s part of a fasting glucose panel. Otherwise, you can eat and drink normally. Bring any medications you’re taking and let your provider know if you have concerns.

During the Test

A healthcare professional will insert a small needle into your arm to draw blood. You may feel a slight pinch, but it usually takes only a few seconds. The blood is then sent to a lab for analysis.

After the Test

You can return to your normal activities immediately. Apply gentle pressure to the site to stop bleeding, and avoid rubbing it. Check with your provider if you experience excessive bruising, swelling, or signs of infection (like redness or fever).

Reference range

Fasting: 70-100 mg/dLN/A

Specimen: serum

Fasting for 8-12 hours required. Water is permitted. Avoid chewing gum and smoking before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

High glucose levels may indicate diabetes, prediabetes, or other metabolic disorders. Repeatedly low levels could signal hypoglycemia, which may require medical attention. Abnormal results may prompt further testing, such as an oral glucose tolerance test or hemoglobin A1c, to explore underlying causes.

Short name

None

Frequently asked questions

What Does a High or Low Glucose Level Mean?
A high glucose reading might mean your body isn’t using insulin properly, or you may have undiagnosed diabetes. A low reading could suggest you’re not eating enough, taking too much insulin, or have another condition affecting blood sugar.
How Often Should I Get This Test?
Your provider will determine how often you need this test based on your health status, medications, or risk factors. For example, people with diabetes may check levels more frequently than others.
Can I Eat or Drink Before the Test?
If fasting is required, avoid food and liquids (except water) for the specified time. If fasting isn’t needed, you can eat and drink normally, but check with your provider first to avoid interfering with results.
  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