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Glucose (Serum or Plasma) – Quantitative Measurement

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

This test measures the amount of glucose (sugar) in your blood, typically taken from serum or plasma. It helps assess blood sugar levels and identify conditions like diabetes or metabolic issues.

Quick summary

["This test checks your blood sugar, important for managing diabetes and other health conditions."]

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

Key facts at a glance

LOINC
26543-9
Short code
Glucose 5h p Glc SerPl-mCnc
Synonyms
Glucose 5h p Glc 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 Is This Test Done?

Doctors order glucose tests to diagnose or monitor diabetes, check for high or low blood sugar, evaluate metabolic disorders, or assess how your body processes carbohydrates. It may also be used before surgeries, during pregnancy, or to screen for conditions like hypoglycemia or hyperglycemia.

What to Expect Before the Test

For a blood draw, you’ll typically fast for 8–12 hours before the test, unless instructed otherwise. If you’re not fasting, your doctor may note this on your results. Avoid smoking or caffeine before the test, as they can affect results.

How the Test Works

Blood is collected via a simple needle prick or catheter. The sample is then processed to measure glucose concentration using an enzymatic method, which detects the sugar’s presence without interference from other substances.

What the Results Mean

Results are usually reported in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). While reference ranges vary by lab, abnormal results may indicate either persistently high (hyperglycemia) or low (hypoglycemia) blood sugar levels, prompting further evaluation.

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

Glucose Level

Frequently asked questions

What does a high glucose level mean?
A high glucose level may signal diabetes, prediabetes, or other metabolic disorders. Repeatedly elevated results could indicate poor blood sugar control, requiring lifestyle changes, medication adjustments, or further testing (e.g., HbA1c).
What does a low glucose level mean?
Low glucose levels (hypoglycemia) can cause dizziness, shakiness, or confusion. While rare in routine testing, they may occur with certain medications, fasting errors, or underlying conditions. Your doctor may recommend monitoring or treatment if results are consistently low.
Does fasting affect this test?
Yes, fasting is critical for accuracy. If you didn’t fast as instructed, your results may be unreliable. Always follow your doctor’s or lab’s specific fasting guidelines to avoid misinterpretation.
  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