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Glucose, Preprandial (Fasting) in Serum/Plasma

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

This test measures your blood sugar level before eating, helping your doctor assess how your body manages glucose (sugar) during fasting.

Quick summary

["A fasting blood sugar test helps check for diabetes or other blood sugar issues before meals."]

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

Key facts at a glance

LOINC
12638-3
Short code
Glucose pre Lac PO SerPl-mCnc
Synonyms
Glucose pre Lac PO SerPl-mCnc
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 This Test Matters

Doctors use fasting blood sugar tests to diagnose conditions like diabetes, monitor existing diabetes management, or evaluate metabolic health. It helps identify whether your body produces enough insulin or if glucose isn’t being processed normally.

What to Expect Before the Test

You’ll need to fast (not eat or drink anything except water) for at least 8 hours before the test. Avoid sugary drinks or snacks. Your blood will be drawn from a vein, usually in your arm, by a healthcare professional.

How the Test Works

A small sample of your blood (either serum or plasma) is taken and analyzed to measure glucose concentration. The test detects how your body handles sugar, often using an enzymatic method to measure the amount present.

What the Results Mean

Results help determine if your blood sugar is within normal ranges or if it’s too high or low, which could signal diabetes, prediabetes, or other metabolic disorders. Your doctor will interpret the results in the context of your overall health.

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.

◆Associated findings1

Short name

Fasting Blood Sugar

Frequently asked questions

How long does it take to get my fasting blood sugar results?
Results are typically available within 1 to 2 business days, depending on your lab. Your doctor will contact you with the final report, so check with them for exact timelines.
Can I eat or drink anything before my fasting blood sugar test?
No, you must fast for at least 8 hours before the test. Only water is allowed. Avoid sugary drinks, snacks, or caffeine to ensure accurate results.
What if my blood sugar is too high or too low on this test?
If your results are outside normal ranges, your doctor may recommend further testing, lifestyle changes, or treatment to manage your blood sugar levels effectively.
  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