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Alpha-Fetoprotein L3 Fraction, Serum/Plasma — Mass Fraction

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

Measures the proportion of total alpha-fetoprotein (AFP) in the L3 form, mainly used as part of prenatal screening for certain fetal chromosomal conditions.

Quick summary

["An AFP-L3 result is a screening marker that must be interpreted alongside other prenatal tests and clinical findings."]

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

Key facts at a glance

LOINC
42332-7
Short code
AFP L3 MFr SerPl
Synonyms
AFP L3 MFr SerPl
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0
Ref high
10
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82105
SNOMED
394971007
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?

Alpha-fetoprotein (AFP) is a protein produced mainly by the developing fetus and liver. The AFP-L3 fraction measures how much of the total AFP in a blood sample is in the L3 form.

Why might I need this test?

This test is most often used with other maternal blood tests and ultrasound during prenatal screening. It can help assess the likelihood of certain fetal conditions, including Down syndrome, but it cannot provide a definitive diagnosis.

How is the test performed?

A serum or plasma sample is collected by drawing blood from a vein. The laboratory measures the amount of AFP-L3 relative to the total AFP and reports the L3 mass fraction.

How do I prepare for the test?

No special preparation or fasting is usually required for the blood draw. Follow the timing and instructions provided by your prenatal care clinician, and tell the laboratory if you are pregnant.

Reference range

Normal: <10 ng/mLN/A

Specimen: serum

No special preparation required. For PSA, avoid sexual activity for 24-48 hours before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

AFP-L3 fraction

Frequently asked questions

Does an abnormal AFP-L3 result mean my baby has Down syndrome?
No. AFP-L3 is one screening marker, and an abnormal result does not confirm Down syndrome or any other condition. Follow-up testing, such as detailed ultrasound or diagnostic genetic testing, may be recommended.
Is AFP-L3 different from a total AFP test?
Yes. A total AFP test measures the overall amount of AFP, while the AFP-L3 test reports the proportion of that AFP in the L3 form.
Does this test require fasting?
Fasting is generally not required. Confirm any timing instructions with your prenatal care clinician because the test is interpreted as part of a screening process.
  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