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Glucose, Substance Concentration in Serum or Plasma

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

This test measures the amount of glucose (sugar) in your blood, typically drawn from a vein or capillary site.

Quick summary

["Glucose levels help monitor blood sugar and identify diabetes or other metabolic conditions."]

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

Key facts at a glance

LOINC
54487-4
Short code
Glucose Wat-sCnc
Synonyms
Glucose Wat-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?

Doctors may order this test to check for diabetes, monitor blood sugar control in people with diabetes, diagnose hypoglycemia (low blood sugar), or evaluate symptoms like excessive thirst, frequent urination, or unexplained weight changes.

What to Expect Before the Test

You may fast (not eat) for 8–12 hours before the test, though some tests can be done without fasting. A healthcare provider will insert a small needle to draw blood from your arm or finger.

What Happens During the Test?

The blood sample is sent to a lab where it is analyzed for glucose concentration using an automated method, often enzymatic or electrochemical.

What Are the Results?

Results are reported in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). Your doctor will interpret the results based on your health history and symptoms.

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 or prediabetes, while persistently low levels can signal hypoglycemia. Frequent monitoring is critical for managing chronic conditions like diabetes to prevent complications such as nerve damage, kidney issues, or heart disease.

Short name

Glucose Level

Frequently asked questions

How often should I get this test?
Your doctor will determine the frequency based on your medical needs—such as whether you have diabetes, prediabetes, or other conditions affecting blood sugar. Follow-up tests may be scheduled every few months or annually.
What do my results mean if they’re outside the normal range?
If your glucose is consistently high, it may mean you have diabetes or insulin resistance. If low, it could indicate hypoglycemia, especially if you experience shakiness, dizziness, or confusion. Always discuss results with your healthcare provider for personalized guidance.
Can I eat or drink anything before this test?
Most glucose tests require fasting (no food or liquids except water) for 8–12 hours before drawing blood. However, some labs may allow a small sip of water if you’re not fasting for another reason, like a procedure. Always confirm with your lab or doctor.
  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