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Glucose in Serum (Fasting)

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

This test measures the amount of glucose (sugar) in your blood after you’ve fasted for 8–12 hours. It helps assess your blood sugar levels and identify risks for diabetes or other metabolic conditions.

Quick summary

["A fasting blood sugar test checks if your body processes sugar normally."]

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

Key facts at a glance

LOINC
11943-8
Short code
GA from UL
Synonyms
GA from UL
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us-estimated-from-ulna-length
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 Matters

Your doctor may order this test if you have symptoms like extreme thirst, frequent urination, fatigue, or unexplained weight changes. It’s also used during routine check-ups, especially for adults over 45 or those with risk factors like obesity, high blood pressure, or a family history of diabetes.

What to Expect Before the Test

You’ll need to fast (not eat or drink anything except water) for 8–12 hours before the test. Avoid sugary drinks or snacks. Let your lab technician know if you’re pregnant, have kidney disease, or take certain medications that might affect results.

How the Test Works

A small blood sample is taken from a vein in your arm. The sample is sent to a lab where glucose levels are measured using an automated method, often an enzymatic or electrochemical technique.

What the Results Mean

Results are typically reported in milligrams per deciliter (mg/dL). A result below the reference range may indicate low blood sugar (hypoglycemia), while values above may signal high blood sugar (hyperglycemia), which could be linked to diabetes or other conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Fasting Serum Glucose

Frequently asked questions

How long does it take to get my results?
Results are usually available within 1–3 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 anything before the test?
No, you must fast for 8–12 hours before the test. Only water is allowed. Check with your doctor if you have questions about specific medications or health conditions that might affect fasting.
What if my blood sugar is too low or too high?
If your results are outside the expected range, your doctor may recommend lifestyle changes (like diet, exercise, or medication) or further testing. They’ll guide you on next steps based on your overall health and symptoms.
  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