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Prenatal Interphase Aneuploidy Screen by Fluorescence In Situ Hybridization (FISH) Analysis

FISH, aneuvision, prenatal FISH, genetic, GPFGT (amnio), GPFGV (CVS), AneuVysion Panel (13, 18, 21, X, Y), AneuVysion Prenatal Panel (13, 18, 21, X, Y)

Test Codes

Amnio: EPIC: LAB6466, CVS: EPIC: LAB6467

Department

Cytology

Specimen Collection Criteria

Collect: 20 mL amniotic fluid or 10 mg chorionic villi tissue in a sterile collection container.

A copy of the requisition must be sent with the specimen.

Rejection Criteria

Specimens arriving in the Laboratory 4 days or more following the original collection date.

Fixed or frozen specimens. 

In-Lab Processing

Specimens are processed immediately upon receipt in the Laboratory.

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 48 hours
Refrigerated (2-8°C or 36-46°F): 96 hours
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days. A backup cell pellet is maintained for two weeks after the case has been signed out.

Laboratory

Royal Oak Cytogenetics Laboratory

Performed

Monday – Friday, 8:00 am – 5:00 pm.
Results available within 7 days of receipt in the Laboratory.

Reference Range

Positive or negative for chromosome aneuploidy. An interpretative report will be provided.

Test Methodology

Fluorescence In Situ Hybridization (FISH) Analysis.

Interpretation

Aneuploidy is detected when the percentage of nuclei with an abnormality exceeds the threshold (normal reference range) established for each probe. The parents of an aneuploid conception have an increased risk of up to 1% beyond the age-related risk for aneuploidy in future pregnancies. It is recommended that decision-making regarding clinical management of the fetus should be based on two of the following: positive FISH results, confirmatory chromosome analysis, or consistent clinical information.

Clinical Utility

While many causes of spontaneous miscarriage have been identified, a chromosome abnormality is observed in up to half of all cases. Aneuploidy, the gain or loss of a chromosome, as well as triploidy (69 chromosomes instead of the normal diploid content of 46 chromosomes) accounts for the majority of these cases. Up to 95% of all chromosome aneuploidy identified prenatally involves gain of chromosomes 13, 18, or 21, along with the X and Y chromosomes. In addition, aneuploidy of these chromosomes accounts for over 80% of all chromosome abnormalities in liveborn infants. 

While standard cytogenetic analysis of amniotic fluid or chorionic villi remains the gold standard for fetal chromosome evaluation, it requires 7-12 days for a final result to be obtained. In certain clinical situations such as advanced maternal age, advanced gestational age, or the presence of an ultrasound anomaly strongly suggestive of aneuploidy, a technique to rapidly identify aneuploidy of chromosomes 13, 18, 21, X, and Y may be helpful. Utilization of a FISH panel to enumerate chromosomes 13, 18, 21, X, and Y applied to either uncultured amniocytes (obtained by amniocentesis) or chorionic villi (obtained by CVS) can provide a result in 1-2 business days. In addition, this test may be useful when rapid evaluation of possible aneuploidy in a newborn is required.

Reference

1. Ward BE et al (1993): Rapid prenatal diagnosis of chromosomal aneuploidies by fluorescence in situ hybridization: clinical experience with 4,500 specimens. Am J Hum Genet: 52, 854-865.
2. American College of Medical Genetics and American Society of Human Genetics (2000): Technical and clinical assessment of fluorescence in situ hybridization: an ACMG/ASHG position statement. I. Technical considerations. Test and Technology Transfer Committee. Genet Med 2: 356-361].

CPT Codes

88271x2 (DNA probe, each), 88274 (Interphase analysis, 25-99 cells).

Contacts

Last Updated

12/30/2022