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FISH - Trisomy 21 / Down Syndrome Test

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FISH - Trisomy 21 / Down Syndrome Test

Short Name: FISH Trisomy 21 Test

Also known as: Fluorescence In Situ Hybridization (FISH), Trisomy 21 Test

FISH - Trisomy 21 / Down Syndrome Test test available at DNA Labs India for ₹6,000. Uses Fluorescence In Situ Hybridization (FISH) on Whole blood / Cord blood / Amniotic fluid / Chorionic villus biopsy samples. Results in Report available within 4 days after sample receipt at the laboratory.. Free home collection in 300+ cities across India.

Genetic TestFemalePrenatal🏠 Home Collection

✍️ Written By

🩺 Medically Reviewed By

Dr SULOCHANA HEMCHANDRA HOLLA

Dr SULOCHANA HEMCHANDRA HOLLA

Consultant Medical Geneticist · Reg: 8532

Last reviewed: September 7, 2026

Overview

The FISH - Trisomy 21 / Down Syndrome Test is performed to diagnose Down Syndrome in the fetus during pregnancy. It helps identify the presence of an extra chromosome 21, enabling early intervention and informed decision-making for high-risk pregnancies.

Test Code
611
Price
₹6,000
Sample Type
Whole blood / Cord blood / Amniotic fluid / Chorionic villus biopsy
Result Time
Report available within 4 days after sample receipt at the laboratory.
Fasting Required
No
Method
Fluorescence In Situ Hybridization (FISH)
Step 1

Sample Collection

Complete and submit the mandatory Chromosome & FISH analysis Requisition Form (Form 17) and Prenatal Genetic Testing Consent Form (Form 18). Consult with a healthcare provider for genetic counseling and to understand the test implications.

Method: Venipuncture for blood, amniocentesis for amniotic fluid, chorionic villus sampling for biopsy

Step 2

Laboratory Analysis

Sample collection is performed by a trained phlebotomist or medical professional using sterile techniques. For amniocentesis or CVS, the procedure is done under ultrasound guidance.

Step 3

Report Delivery

Ensure the sample is labeled correctly and shipped at 18-22°C as per instructions. Avoid hemolysis or contamination. Await results within the specified turnaround time.

Timeline: Report available within 4 days after sample receipt at the laboratory.

Patient Instructions

1
Before the Test:Consult with your healthcare provider to discuss the need for the test, complete mandatory forms, and understand the risks and benefits.
2
During the Test:Sample collection will be performed as per the method specified (blood draw, amniocentesis, or CVS). Follow the instructions of the medical professional.
3
After the Test:After sample collection, monitor for any discomfort and follow up with your doctor for results. Results are typically available within 4 days.

About This Test

Who Should Get This Test

The FISH - Trisomy 21 / Down Syndrome Test is performed to diagnose Down Syndrome in the fetus during pregnancy. It helps identify the presence of an extra chromosome 21, enabling early intervention and informed decision-making for high-risk pregnancies.

How to Prepare

  • Complete and submit Form 17 and Form 18 before sample collection
  • Collect sample in the specified container (e.g., Green Top tubes for blood)
  • Ship the sample at 18-22°C immediately after collection
  • Ensure proper labeling with patient details and test information
  • Avoid delays in transportation to maintain sample stability

Doctor's Notes

Reviewed by — MBBS, MD (Medical Genetics) · Reg. No. 8532

"Early detection through FISH testing for Trisomy 21 allows for informed decision-making and planning for Down Syndrome management during pregnancy."

Last medically reviewed: September 7, 2026

Test Parameters & Specifications

Sample TypeWhole blood / Cord blood / Amniotic fluid / Chorionic villus biopsy
Sample Volume5 mL (3 mL min.) for blood, 5 mL for amniotic fluid, 2 g for biopsy
ContainerGreen Top (Sodium Heparin) tubes for blood, sterile screw capped container for amniotic fluid, normal saline for biopsy
Collection MethodVenipuncture for blood, amniocentesis for amniotic fluid, chorionic villus sampling for biopsy

Sample Stability

Room Temperature: 48 hours
Sample Rejection Criteria:
  • Hemolyzed sample
  • Incorrect container or insufficient volume
  • Missing or incomplete mandatory forms
  • Sample contaminated or degraded
  • Improper labeling or identification

Understanding Your Results

The FISH test for Trisomy 21 detects the presence of an extra copy of chromosome 21 in fetal cells. Results indicate whether the fetus is at risk for Down Syndrome, guiding further medical management.
📊

Positive

Indicates presence of trisomy 21, suggestive of Down Syndrome. Confirmatory testing like karyotyping is recommended.

📊

Negative

Indicates normal chromosome 21 count, reducing the likelihood of Down Syndrome.

📊

Inconclusive

Insufficient cells or technical error detected. Repeat testing or alternative methods may be needed.

⚠️ When to Consult a Doctor:

If the test result is positive, consult a genetic counselor or obstetrician immediately for further evaluation, management options, and support. Even with negative results, discuss any concerns with your healthcare provider for comprehensive prenatal care.

Limitations

  • ⚠FISH is a targeted test and may not detect other chromosomal abnormalities
  • ⚠False positives or negatives can occur in rare cases
  • ⚠Confirmatory karyotyping is recommended for positive results
  • ⚠Limited to detecting specific chromosomal anomalies, not structural variations
  • ⚠Requires adequate sample quality and quantity

Risks & Considerations

  • ●Risk of miscarriage for invasive procedures like amniocentesis or CVS (approx. 0.1-0.3%)
  • ●Infection at the collection site
  • ●Cramping or mild discomfort
  • ●Very low risk of fetal injury for invasive tests

Interfering Factors

  • ●Sample contamination
  • ●Insufficient cell count in the sample
  • ●Maternal cell contamination in prenatal specimens
  • ●Hemolyzed or degraded sample
  • ●Technical errors during FISH processing

Compare With Similar Tests

TestFISH - Trisomy 21 / Down Syndrome TestChorionic Villus Sampling (CVS)AmniocentesisNon-Invasive Prenatal Testing (NIPT)Karyotyping
ComparisonFISH - Trisomy 21 / Down Syndrome Test

Frequently Asked Questions

What is the FISH - Trisomy 21 / Down Syndrome Test?
The FISH (Fluorescence In Situ Hybridization) test is a rapid genetic test that detects the presence of an extra chromosome 21 in fetal cells, used to diagnose Down Syndrome during pregnancy.
Why is the FISH Trisomy 21 test done?
This test is performed to diagnose Down Syndrome in the fetus, especially for high-risk pregnancies, such as women over 35, with family history, or abnormal ultrasound findings.
Who should consider getting this test?
Women who are 35 years or older, have a family history of Down Syndrome, previous child with chromosomal issues, or abnormal screening test results should consider this test.
How is the test performed?
The test uses cells from amniotic fluid, chorionic villus biopsy, or cord blood. FISH technology fluorescently labels chromosome 21 to detect abnormalities.
What samples are required for the test?
Samples can be 5 mL whole blood or cord blood in Green Top tubes, 5 mL amniotic fluid in a sterile container, or 2 g chorionic villus biopsy in normal saline.
Is fasting required for the FISH Trisomy 21 test?
No, fasting is not required. However, mandatory forms must be completed before sample collection.
How long does it take to get the test results?
Results are typically available within 4 days after the sample reaches the laboratory, with reports delivered via online portal, email, or WhatsApp.
What are the risks associated with this test?
For invasive procedures like amniocentesis or CVS, there is a small risk of miscarriage (0.1-0.3%), infection, or cramping. Blood-based sampling has minimal risks.
What does a positive result mean?
A positive result indicates the presence of an extra chromosome 21, suggesting Down Syndrome. Confirmatory testing like karyotyping is recommended for verification.
What does a negative result mean?
A negative result means no extra chromosome 21 was detected, reducing the likelihood of Down Syndrome. However, it does not rule out all genetic conditions.
Can this test detect other chromosomal abnormalities?
No, the FISH Trisomy 21 test specifically targets chromosome 21. It does not detect other chromosomal or genetic disorders; additional tests may be needed.
How accurate is the FISH test for Down Syndrome?
The FISH test is highly accurate for detecting trisomy 21, with sensitivity and specificity over 99% when performed correctly. However, confirmatory tests are advised for positive results.
Worried about the process? Our certified phlebotomists collect thousands of samples every month across India. The process takes under 5 minutes and is virtually painless. Questions? Message us on WhatsApp — we're here 7 days a week.

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