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Fasting Insulin, Serum/Plasma — Concentration

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

Measures insulin in a blood sample collected after fasting. It is often used with blood glucose testing to evaluate how the body handles blood sugar.

Quick summary

["A fasting insulin level can help assess how well the body regulates blood sugar and how sensitive the body's cells are to insulin."]

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

Key facts at a glance

LOINC
27873-9
Short code
Insulin p fast SerPl-aCnc
Synonyms
Insulin p fast SerPl-aCnc
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 present after a period of fasting. Insulin is a hormone made by the pancreas that helps glucose enter the body's cells for energy.

Why might I need this test?

A clinician may order this test to help evaluate blood sugar control, insulin resistance, or how the pancreas responds to a rise in blood glucose. It is commonly interpreted together with a simultaneous or nearby glucose test.

How is the test performed?

A healthcare professional draws blood from a vein, usually from the inner elbow. The sample may be tested as serum or plasma, and the laboratory measures the insulin concentration using an approved laboratory method.

How do I prepare for the test?

You may be asked to fast for about 8 to 12 hours before the blood draw. Drink plain water during the fasting period unless your clinician gives different instructions, and do not stop medications unless instructed to do so.

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 this test diagnose diabetes?
Not by itself. Fasting insulin is usually interpreted with blood glucose and other clinical information rather than used as a stand-alone diagnostic test.
How long do I need to fast?
The usual fasting period is about 8 to 12 hours, but follow the specific instructions provided by the laboratory or clinician. Plain water is generally allowed.
Can I take my medicines before the test?
Continue medicines as directed unless your clinician tells you otherwise. Some medicines can affect insulin and glucose levels, so mention all medicines and supplements when the test is ordered.
  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