FISH – PRODUCTS OF CONCEPTION

Fluorescence In Situ Hybridization – Products of Conception

Test Overview

CPT Code(s)

88233-52, 88271×3, 88275, 88291

Methodology

Harvest/Hybridization/Microscopy/Interpretation

Specimen Requirements

Placenta, umbilical cord, and internal fetal organs are all suitable for analysis.  If possible, please send chorionic villi.

Container:  Sterile, leak-proof containers with transport media or sterile saline (i.e. Hanks Balanced Salt Solution). Do not place in formalin.

Optimal Quantity: 1x1x1 cm of at least two fetal tissues, one being chorionic villi

Minimum Quantity: 1 fetal tissue

Storage: Room Temperature

Stability at Room Temperature: 8 hours, then refrigerate

Transportation: Avoid freezing or heating over 35OC

Turnaround Time

Final report in 24-48 hours for 90% of cases

Test Details

Clinical Significance

Fluorescence in situ hybridization (FISH) is a sensitive method to detect chromosome abnormalities.  Because of its ability, FISH can detect the most common aneuploidy in uncultured amniocytes rapidly (within 24-48 hours) and thus offers a rapid and reliable assay for detecting chromosome abnormalities in a prenatal setting.  However, FISH technology is complementary to routine chromosome analysis and cannot substitute routine chromosome analysis and FISH diagnostic testing is not recommended as an isolated test without chromosome analysis for the diagnosis of the common aneuploidy conditions.

Clinical Background

One of the major limitations with reference to chromosome analysis on products of conception is the tissue viability.  Since more than 50% of first trimester abortuses have chromosome abnormalities, failure to get chromosome results can have significant clinical implications for the parents.  Decreased viability can contribute up to 25% of samples not getting any chromosome results.  However, rapid FISH analysis can overcome this tissue viability limitation since interphase FISH analysis can be performed on non-viable tissues.  Since  monosomy X and trisomy of chromosome 16 account for the most chromosome abnormalities in first trimester abortuses, rapid interphase FISH using probes for the most common aneuploidies can provide results even in those cases where routine chromosome analysis is not successful.  FISH on uncultured products of conceptions samples can be a valuable and viable option when routine chromosome analysis is not successful.  In our laboratory, we offer a reflex test to perform interphase FISH on uncultured products of conception samples that failed to grow in culture.

Methods

Uncultured products of conception samples are cleaned for maternal decidua and harvested using routine methods and hybridized with the probes for chromosomes 13, 16, 18, 21, X and Y.   After hybridization and post-hybridization washes, the slides are analyzed under a fluorescence microscope equipped with epifluorescence and appropriate filter sets.  Analysis and scoring is carried out by two certified technologists in a blinded fashion with each scoring a minimum of 50 interphase nuclei.  Results are reviewed by both the laboratory manager and the director.

13 / 21                                    RB1 / D21S259,D21S341,D21S342                         Abbott (cat # 35-171078)

18 / X / Y                                 D18Z1 / DXZ1 / DYZ3                                              Abbott (cat # 35-171077)

16                                            D16Z2                                                                      Abbott (cat # 32-131016)

Interpretation of Results

The morphologic interpretation and correlation of results on all cases is performed by a board-certified doctoral level scientist (laboratory director). The final report has a narrative description of results.  If abnormalities are present, they are explained in a paragraph which helps to clarify and correlate chromosomal findings with phenotype. References are included in the report to help the referring physician with interpretation, which include books or journals that contain appropriate information. Recommendations are made as to any additional testing, if necessary.