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Glucose in Serum (Fasting or Random)

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

This test measures your blood sugar level, which helps doctors check for conditions like diabetes or how your body processes glucose.

Quick summary

["Blood sugar levels indicate whether your body is managing glucose efficiently."]

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

Key facts at a glance

LOINC
72648-9
Short code
Glucose ser - synv fld-SCDiff
Synonyms
Glucose ser - synv fld-SCDiff
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

Blood sugar levels can fluctuate for many reasons, including diet, stress, or underlying health issues. This test helps monitor how your body uses glucose, which is essential for energy and overall health.

What to Expect Before the Test

For fasting glucose tests, you’ll typically fast for 8–12 hours before the blood draw. Random glucose tests can be done at any time. Bring your medical records if you have diabetes or other conditions that affect blood sugar.

How the Test Works

A small blood sample is taken from your arm. The lab analyzes the sample to measure glucose concentration using an enzymatic method, which detects glucose without affecting other substances in the blood.

Common Reasons for Testing

Doctors may order this test to diagnose diabetes, check for prediabetes, evaluate symptoms like excessive thirst or fatigue, or monitor treatment progress for conditions like hypoglycemia.

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.

Clinical Significance

Short name

Glucose Level

Frequently asked questions

High or low blood sugar levels can signal diabetes, insulin resistance, or other metabolic disorders. Repeatedly elevated or low readings may require further evaluation, including lifestyle changes or medication adjustments.
This test alone doesn’t diagnose diabetes—your doctor may also consider symptoms, family history, or other tests like HbA1c.
If you have diabetes, this test helps track how well your current treatment is controlling your blood sugar.
Fasting tests are more reliable for diagnosing diabetes, but random tests can be useful for monitoring acute changes, such as after a meal or illness.
What happens if my results are out of range?
Your doctor will discuss results with you and may recommend changes to diet, exercise, or treatment. Follow-up tests or additional questions may be needed to understand the cause.
  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