FISH- Trisomy 21 Test: Booking, Price, and Results
About FISH- Trisomy 21 Test: Booking, Price, and Results
| Field | Value |
|---|---|
| Also Known As | FISH for Down Syndrome, Fluorescence In Situ Hybridisation - Trisomy 21, Chromosome 21 Aneuploidy FISH, Interphase FISH Trisomy 21 |
| Sample Type | Peripheral blood (postnatal); amniotic fluid or chorionic villus sample (prenatal) |
| Fasting Required | No fasting required |
| Report Time | 3 days |
| Recommended For | Pregnant women with high-risk screening results, advanced maternal age (35 years or older), abnormal ultrasound findings, previous affected pregnancy; newborns with suspected Down syndrome features |
| Price | Starting at ₹3,200 |
What is a FISH-Trisomy 21 Test?
The FISH-Trisomy 21 test is a genetic test that detects whether a person has an extra copy of chromosome 21, the chromosomal change that causes Down syndrome. FISH stands for Fluorescence In Situ Hybridisation, a laboratory technique that uses fluorescently labelled DNA probes to count chromosomes in cells. The test is also known as the FISH for Down Syndrome or Interphase FISH Trisomy 21. Depending on when it is performed, the sample used may be peripheral blood, amniotic fluid, or chorionic villus tissue.
What Does a FISH-Trisomy 21 Test Measure?
The FISH-Trisomy 21 test analyses the number of copies of chromosome 21 present in a cell. Fluorescent probes attach to specific sites on chromosome 21, and a specialist counts the glowing signals under a microscope. The findings are compared with expected normal values.
| Parameter | What It Indicates |
|---|---|
| Chromosome 21 copy number | Whether cells carry 2 (normal) or 3 (trisomy) copies of chromosome 21 |
| Signal count per cell | 2 signals = normal; 3 signals = trisomy 21 (Down syndrome) |
Why is a FISH-Trisomy 21 Test Done?
A doctor may request the FISH-Trisomy 21 test in specific clinical situations, both during pregnancy and after birth.
Common Symptoms That May Require This Test
The following situations commonly lead to this test being recommended:
- High-risk result on a first-trimester prenatal screening test
- Advanced maternal age (35 years or older at the time of delivery)
- Abnormal findings on a foetal anomaly ultrasound scan
- Previous child born with Down syndrome or another chromosomal condition
- Family history of chromosomal abnormalities
- Newborn showing physical features associated with Down syndrome, such as low muscle tone or characteristic facial features
- Abnormal cell-free DNA (cfDNA) or non-invasive prenatal test (NIPT) result
Conditions This Test Can Help Detect
This test can help identify the following conditions:
- Free trisomy 21 (Down syndrome), where all cells carry an extra chromosome 21, accounting for around 95% of cases
- Mosaic Down syndrome, where only some cells carry the additional chromosome 21
- Translocation Down syndrome, where part of chromosome 21 is attached to another chromosome
FISH-Trisomy 21 Test During Pregnancy
Prenatal screening for Down syndrome is routinely offered to all pregnant women. When screening results indicate a high risk, the FISH-Trisomy 21 test is used to confirm or rule out the diagnosis in the foetus. The risk of trisomy 21 increases with maternal age; for example, the risk at age 40 is approximately 1 in 100, compared with 1 in 1,500 at age 20. The test can be performed on amniotic fluid or chorionic villus samples obtained by amniocentesis or CVS procedures.
How to Prepare and What to Expect
No special preparation is needed before the FISH-Trisomy 21 test procedure, but there are a few practical steps to be aware of.
Do You Need to Fast?
No. Fasting is not required before this test. You may eat and drink as normal before your appointment.
Practical Tips Before Your Test
Keep the following in mind before attending your appointment:
- Bring a detailed clinical history, including your symptoms, previous screening results, and family history, as this is required for the test.
- Carry your signed PNDT (Pre-Natal Diagnostic Techniques) consent form, which is mandatory under PCPNDT guidelines.
- Inform your doctor about any medications or supplements you are currently taking.
- If the sample is being collected prenatally, bring your anomaly scan report.
- Wear comfortable, loose clothing to make the sample collection process easier.
- Consider discussing the test with a genetic counsellor before proceeding, to understand what the results may mean for you.
Step-by-Step Procedure
The collection process differs depending on whether the test is prenatal or postnatal.
For postnatal testing (newborns and children):
- A healthcare professional will clean the skin over a vein, usually in the arm.
- A small blood sample of 3 ml is drawn into a sodium heparin (green-top) tube.
- The sample is labelled and stored at 2-8°C for safe transport.
- The sample is sent to the laboratory, where fluorescent probes targeting chromosome 21 are applied to the cells.
- A specialist counts the fluorescent signals in at least 50 cells using a fluorescence microscope.
- Results are matched against reference values, and a report is prepared within 3 days.
For prenatal testing:
- A doctor performs amniocentesis (usually between 15 and 20 weeks of pregnancy) to collect a small amount of amniotic fluid, or a CVS procedure to collect placental tissue.
- The sample is sent to the laboratory promptly under the required temperature conditions.
- FISH probes specific to chromosome 21 are applied to uncultured cells from the sample.
- Signal counts are analysed by a trained technologist under fluorescence microscopy.
- A report is issued within the agreed turnaround time.
Factors That Can Affect Accuracy
The following factors may influence the reliability of the test result:
- Maternal cell contamination of an amniotic fluid sample
- Insufficient cell count in the sample due to poor sample quality
- Improper handling or transport of the sample outside the recommended temperature range
- FISH does not detect structural chromosomal abnormalities or all forms of mosaicism
- The experience and training of the laboratory personnel in reading the signals
Understanding Your FISH-Trisomy 21 Test Results
Results from the FISH-Trisomy 21 test reflect the number of chromosome 21 copies detected in the cells analysed. A report should always be reviewed with your doctor or a genetic counsellor, who will assess findings alongside your full clinical picture.
| Chromosome 21 Signals per Cell | Interpretation |
|---|---|
| 2 signals | Normal (disomy); trisomy 21 not detected |
| 3 signals | Trisomy 21 detected (consistent with Down syndrome) |
These ranges are general guidelines. Your doctor will interpret your results based on your age, health history, and other factors. Always consult a qualified healthcare professional for personalised medical advice.
An abnormal result showing 3 signals indicates the presence of an extra chromosome 21. This may represent free trisomy 21, mosaic trisomy 21, or a translocation involving chromosome 21. Because FISH does not distinguish between these types, a complete karyotype analysis is recommended to confirm the finding and determine the exact chromosomal arrangement.
How to Maintain General Wellness
As this is a chromosomal finding, no lifestyle changes can alter the result. However, the following steps can support informed decision-making:
- Attend genetic counselling before and after testing to better understand your results.
- Women aged 35 and older are advised to discuss prenatal screening options early in pregnancy with their obstetrician.
- Regardless of test outcome, regular antenatal care and monitoring support a healthy pregnancy.
Lupin Diagnostics FISH-Trisomy 21 Test Price
The FISH-Trisomy 21 test cost at Lupin Diagnostics starts at ₹3,200. This test requires a visit to a Lupin Diagnostics centre; home collection is not available for this test.
| City | Approximate Price (₹) |
|---|---|
| BHOPAL | 3200 |
| CHENNAI | 3200 |
| HYDERABAD | 3200 |
| KOLKATA | 3200 |
| NAVI MUMBAI | 3200 |
| PUNE | 3200 |
Disclaimer: Prices are indicative and may vary by location. Please confirm the current price at the time of booking.
How to Book
You can book the FISH- Trisomy 21 test online through the following steps:
- Select the test on the Lupin Diagnostics website.
- Choose your city and preferred centre location.
- Visit the centre at your scheduled time for sample collection.
- Receive your report via email or WhatsApp within the stipulated turnaround time.
Frequently Asked Questions
The FISH-Trisomy 21 test is used to detect whether a person has three copies of chromosome 21 instead of the normal two. This extra copy causes Down syndrome. The test is used both during pregnancy to check the foetus and after birth if a newborn shows features associated with the condition.
Studies show the FISH-Trisomy 21 test has a sensitivity and specificity of greater than 99% for detecting Trisomy 21. However, because FISH does not detect all chromosomal abnormalities, results are typically confirmed with a full karyotype analysis before any major decisions are made.
No fasting is needed. You should bring a detailed clinical history and your signed PNDT consent form to your appointment. Let your doctor know about any medications you are currently taking before the test.
The FISH-Trisomy 21 test report is delivered within 3 days of the sample being received and processed at the laboratory.
Yes. When a newborn shows physical features that may suggest Down syndrome, such as low muscle tone, a flat facial profile, or other characteristic signs, a doctor may order the FISH-Trisomy 21 test using a peripheral blood sample.
FISH provides a rapid and highly accurate result for chromosome 21 copy number. However, it cannot determine whether the trisomy is due to a free chromosome, a translocation, or mosaicism. A complete karyotype is recommended alongside FISH for a full chromosomal picture.
Yes. Genetic counselling before the FISH-Trisomy 21 test is strongly advisable. A counsellor can explain what the test involves, what different results may mean, and what options are available based on the findings.
FISH- Trisomy 21 Test: Booking, Price, and Results
