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Chromosomal Analysis for Aneuploidy Detection (FISH - Fluorescence In Situ Hybridization)

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

This test checks for abnormal chromosome numbers, which can occur in conditions like Down syndrome or other genetic disorders. It uses fluorescent probes to identify specific chromosomes in your cells.

Quick summary

["This test helps detect genetic imbalances that may affect pregnancy, cancer risk, or other health concerns."]

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

Key facts at a glance

LOINC
84919-0
Short code
Chr 21 aneup Amn/CVS Ql FISH
Synonyms
Chr 21 aneup Amn/CVS Ql FISH
Category
chemistry
Sample
fluid
Container
Sterile tube
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
fish
Specimen volume
2-5 mL
Stability
Room temperature: 2h, Refrigerated: 24h
Hemolysis max
300
TAT
4–24 hours
Order
routine

What This Test Measures

The test analyzes chromosomes in cells from a sample (often amniotic fluid, fetal cells, or blood) using fluorescent probes. It looks for extra or missing chromosomes (aneuploidy), particularly chromosome 21, which is linked to Down syndrome.

How the Sample Is Collected

The sample is typically taken during pregnancy (e.g., amniocentesis or chorionic villus sampling) or from a blood draw. The test examines cells under a microscope to detect fluorescent signals indicating chromosome abnormalities.

When You Might Need This Test

This test is often recommended for women over 35 or those with a family history of genetic disorders, or if there are concerns about pregnancy complications. It can also be used in cancer screening to assess genetic instability.

What to Expect Before the Test

If done during pregnancy, you may receive mild discomfort or cramping. If from blood, you’ll have a standard venipuncture. Follow any specific instructions your provider gives, such as fasting or avoiding certain medications.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Aneuploidy Screening by FISH

Frequently asked questions

Why might this test be important for my health?
Detecting aneuploidy early can help guide pregnancy management, cancer treatment planning, or genetic counseling. For example, identifying extra chromosome 21 helps diagnose Down syndrome, while abnormal findings in cancer cells may suggest a higher risk of recurrence or resistance to treatment.
How long will results take?
Results typically take 1–2 weeks, depending on the lab and sample type. Your healthcare provider will discuss the findings with you once they’re ready.
Can I prepare for this test in any special way?
No special preparation is usually needed unless your provider specifies. For blood tests, avoid strenuous activity the day before. If the test is part of a pregnancy procedure, follow your provider’s instructions for timing and safety.
  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