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​Fluorescence in situ hybridization (FISH) - Amniotic Fluid

Cytogenetics


​Ordering Recommendation

  • ​​Optimal timing for specimen collection is between 14 to 18 weeks of gestation, but specimens collected at other weeks of gestation are also accepted
  • FISH for aneuploidy screening is done for high risk indications only (see relevant clinical history section)
  • A complete chromosome analysis will be performed from the amniotic fluid collected (see “Chromosome analysis-Amniotic Fluid” test)

​ ​Specimen Requirements

Type​
  • ​Amniotic Fluid
​Container
  • ​Preferred Collection Container: one sterile 15 ml tubes such as Corning or BD
​Collection Procedure
  • ​Specimen must be accompanied by a completed test requisition
  • Failure to include relevant patient information may result in test results being delayed or discontinued
​Required Volume
  • ​Optimal Volume: 3-5 ml in a third tube, in addition to the required 15-20 ml for chromosome analysis
  • Minimum Volume: All samples are accepted regardless of volume
    (Submitting the minimum volume makes it impossible to repeat the test or perform confirmatory/reflex testing. In some situations, a minimum volume may require a second collection.)
​Stability/Storage
  • ​Specimens are to be kept and delivered at room temperature
  • Do not freeze specimen or expose to extreme heat
Grounds for Rejection​

Testing Information​ ​

Availability​
  • ​Specimens are received in the Cytogenetics Laboratory weekdays from 8:00 a.m. to 5:00 p.m.
  • There is a Cytogenetics technologist on call Saturday, Sunday and statutory holidays from 8:30 a.m. to 5:00 p.m. for urgent specimens only. This person can be reached through Royal University Hospital Switchboard (655-1000).
  • Booking of specimens from outside the Saskatoon Health Region is recommended for tracking purposes
Testing Site​Cytogenetics Laboratory
Ellis Hall Ground Floor, Room 35
Royal University Hospital, 103 Hospital Drive
Saskatoon SK S7N 0W8
Phone: 306-655-1706
FAX: 306-655-6462
Results Reporting​
  • ​3-7 days
​Reflex Testing
  • ​A concurrent chromosome analysis is done in all cases
​Methodology
  • ​Direct amniocyte preparation and fluorescence in situ hybridization (FISH) with probes for enumeration of chromosomes 13, 18, 21, X and Y
​Clinical Interpretation
  • ​Diagnosis of aneuploidy syndromes: Down, Patau, Edwards, Turner, Klinefelter
  • Anomaly designation follows the most recent edition of the International System for Human Cytogenetic Nomenclature
​Specimen Retention
  • ​FISH slides are kept for one year
Alternate Test Names​
  • Genetic Amniocentesis
  • FISH
​Additional Comments
  • ​Molecular genetics (DNA) testing is only done through referral to Medical Genetics (phone: 655-1692)
Reference Ranges
  • Two copies of the probes
  • Females: two copies of the X chromosome probe
  • Males: one copy of the X and one copy of the Y probes

Testing Ordering Requirements​ ​

​Forms Required
  • ​Cytogenetic Prenatal Diagnosis Requisition obtained from the Cytogenetics Laboratory

Patient History​ ​

​Relevant Clinical History
  • ​Prenatal screening risk of aneuploidy greater than 1: 50
  • Ultrasound abnormality associated with increased risk of aneuploidy
  • Multiple soft markers by ultrasound
  • Multiple anomalies
  • Severe early fetal growth retardation
  • Late gestational age
  • Potential for fetal therapy


If you choose to print this information, it is valid only on date of print.

Laboratory Controlled Document LSM-162 v3

Last Modified: Monday, December 11, 2017 |
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