Fluorescence In Situ Hybridization – Amniotic Fluid

Test Overview

CPT Code(s)

88235-52, 88271×2, 88275, 88291



Specimen Requirements

Container: Two 15 ml sterile leak-proof conical tubes (discard 1st milliliter to avoid maternal cell contamination)

Optimal Quantity: 20-25 ml

Minimum Quantity: 10 ml

Storage: Room Temperature

Stability at Room Temperature: 8 hours, then refrigerate

Transportation: Avoid freezing or heating over 35OC

Turnaround Time

Final report in 24 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

Ever since the studies in the late 1970 and 1980 showing the feasibility of detecting chromosome abnormalities using FISH on cultured cells, FISH has become an invaluable tool for rapid diagnosis of aneuploidy in prenatal samples, especially those with high risk pregnancies.  Unlike chromosome analysis which takes a minimum of 7-10 days for a karyotype, rapid FISH can detect chromosome aneuploidy in 24-48 hours thus providing valuable information to both the physicians and the parents to make informed decisions.  After several studies have shown conclusive evidence that the rapid FISH on uncultured amniocytes is accurate, the Federal Drug Administration (FDA) has cleared the Aneuvysion test for clinical applications and is now routinely offered in most clinical diagnostic laboratories.


Approximately 5 ml of amniotic fluid is collected and harvested using routine methods and hybridized with the probes for chromosomes 13, 18, 21, X and Y.  Our laboratory uses the FDA cleared Aneuvysion probes from Abbott.  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)

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.