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Insulin, 12-Hour Fasting, Serum/Plasma — Mass Concentration

Published: August 9, 2026Updated: August 17, 2026

Measures fasting insulin in serum or plasma to help assess how the body handles blood sugar and insulin.

Quick summary

["A fasting insulin test helps evaluate blood sugar regulation and insulin production or resistance."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
1573-5
Short code
Insulin p 12h fast SerPl-mCnc
Synonyms
Insulin p 12h fast SerPl-mCnc
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
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

What is this test?

This blood test measures the amount of insulin in your blood after a 12-hour fast. Insulin is a hormone that helps glucose enter cells for energy.

Why might I need this test?

A provider may order it to evaluate blood sugar regulation, investigate possible insulin resistance, or help assess and monitor diabetes treatment. It is often interpreted together with a blood glucose test.

How is the test performed?

A blood sample is collected from a vein and tested to determine the concentration of insulin. The sample is usually taken after you have fasted for 12 hours.

How do I prepare for the test?

Follow your provider's instructions and do not eat or drink anything except plain water for 12 hours before the blood draw, unless you are told otherwise. Taking medicines right before the test can affect the result, so ask your provider how to handle them.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Fasting Insulin

Frequently asked questions

Does fasting insulin diagnose diabetes?
Not by itself. It is usually interpreted with fasting glucose, blood sugar monitoring, symptoms, and sometimes additional tests.
How long must I fast before this test?
The test is generally performed after a 12-hour fast. Follow any specific instructions from your healthcare provider, especially if you take diabetes medicines.
Can I drink water during the fast?
Plain water is usually allowed, but check with the laboratory or your provider. Avoid beverages other than water unless your care team specifically says otherwise.
  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 17, 2026. · Read our editorial policy