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Fragile X Syndrome, Fetal Analysis

Test Number 481718
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CPT

81243; 81244
Synonyms
  • Fragile X testing
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  • Updated on 04/03/2025

Test Details

Methodology

Fragile X syndrome: Polymerase chain reaction (PCR) followed by capillary electrophoresis and methylation PCR analysis

Maternal cell contamination analysis (MCC): Analysis of short tandem repeat markers by multiplex fluorescent polymerase chain reaction (PCR) and capillary electrophoresis

Result Turnaround Time

8 - 14 days. If culture is needed, an additional 14 - 21 days may be required. Additional culture fee may be applied.

Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.

Use

This test is used for prenatal diagnosis for pregnancies at risk for fragile X syndrome (FMR1).

Special Instructions

Labcorp clients with eight-digit client account numbers should call 800-345-4363, and Labcorp Genetics & Women's Health clients with six-digit client/subclient account numbers should call 800-255-7357 to speak with a laboratory genetic coordinator before collecting specimens. In some circumstances, specimens from both parents and other family members may be required. All fetal specimens, including cord blood, must be accompanied by a maternal blood, PurFlock buccal swab kit or Oragene Dx 500 saliva kit for maternal cell contamination (MCC). A separate requisition should be submitted with the maternal specimen.

Limitations

Technologies used do not detect germline mosaicism and do not rule out the presence of large chromosomal aberrations including rearrangements and gene fusions, or variants in regions or genes not included in this test, or possible inter/intragenic interactions between variants, or repeat expansions. Variant classification and/or interpretation may change with time if more information becomes available. False positive or false negative results may occur for reasons that include: rare genetic variants, sex chromosome abnormalities, pseudogene interference, blood transfusions, bone marrow transplantation, somatic or tissue-specific mosaicism, mislabeled samples or erroneous representation of family relationships. This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.

Specimen Requirements

Specimen

Chorionic villus sample (CVS), or cultured CVS or cultured amniotic fluid, or cord blood. Direct amniotic fluid specimens with gestational ages less than 19 weeks or specimens that do not meet minimum volume requirements will be placed in culture. Additional culture fee may be applied.

Chorionic villus sample (CVS), or cultured CVS or cultured amniotic fluid, or cord blood. Fragile X analysis is not performed on direct amniotic fluid specimens; submitted specimens will be placed into culture. Direct CVS specimens are accepted for testing. Additional culture fees may be applied.

Chorionic villus sample (CVS), or cultured CVS or cultured amniotic fluid, or cord blood. Direct amniotic fluid specimens with gestational ages less than 19 weeks or specimens that do not meet minimum volume requirements will be placed in culture. Additional culture fee may be applied.

Volume

Amniotic fluid: 20 mL from >19 weeks gestational age; or CVS: 10 mg; or amniotic fluid or CVS culture: two confluent T-25 flasks; or cord blood: 4 mL. If amniotic fluid or CVS are cultured at another facility, please maintain backup cultures.

CVS: 10 mg; or amniotic fluid or CVS culture: two confluent T-25 flasks; or cord blood: 4 mL. If amniotic fluid or CVS are cultured at another facility, please maintain backup cultures.

Amniotic fluid: 20 mL from >19 weeks gestational age; or CVS: 10 mg; or amniotic fluid or CVS culture: two confluent T-25 flasks; or cord blood: 4 mL. If amniotic fluid or CVS are cultured at another facility, please maintain backup cultures.

Minimum Volume

Amniotic fluid: 20 mL from >19 weeks gestational age; or CVS: 10 mg; or amniotic fluid or CVS culture: two confluent T-25 flasks; or cord blood: 3 mL

CVS: 10 mg; or amniotic fluid or CVS culture: two confluent T-25 flasks; or cord blood: 3 mL

Amniotic fluid: 20 mL from >19 weeks gestational age; or CVS: 10 mg; or amniotic fluid or CVS culture: two confluent T-25 flasks; or cord blood: 3 mL

Container

Amniotic fluid or CVS: sterile plastic conical tube or T-25 flask

Cord blood: Yellow-top (ACD-A) or lavender-top (EDTA) tubes

Collection Instructions

Standard sterile techniques; transfer aseptically to sterile tubes.

Amniotic fluid: Discard first 2 mL of fluid aspirated to avoid maternal cell contamination.

Stability Requirements

Please ship expedited at room temperature.

Storage Instructions

Maintain specimen at room temperature. Do not freeze.

Causes for Rejection

Frozen or hemolyzed specimen; quantity not sufficient for analysis; improper container

References

Hunter JE, Berry-Kravis H, Hipp H, et al, editors. In: GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993. 1998 Jun 16 [updated 2019 Nov 21].20301558
Nagan, M, Faulkner NE, Curtis C, Schrijver I, MCC Guidelines Working Group of the Association for Molecular Pathology Clininical Practice Committee. Laboratory guidelines for detection, interpretation, and reporting of maternal cell contamination in prenatal analyses a report of the association for molecular pathology. J Mol Diagn. 2011 Jan;13(1):7-11.21227389
Spector E, Behlmann A, Kronquist K, et al. Laboratory testing for fragile X, 2021 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG). Genet Med. 2021 May;23(5):799-812.33795824

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
481718 Fragile X, Fetal Analysis 21759-6 481702 Ethnicity 42784-9
481718 Fragile X, Fetal Analysis 21759-6 481703 Specimen Type 31208-2
481718 Fragile X, Fetal Analysis 21759-6 481704 Genetic Counselor 89993-0
481718 Fragile X, Fetal Analysis 21759-6 481705 Indication 42349-1
481718 Fragile X, Fetal Analysis 21759-6 481706 Fetal ID 11951-1
481718 Fragile X, Fetal Analysis 21759-6 481707 Result: 21759-6
481718 Fragile X, Fetal Analysis 21759-6 481708 Interpretation 53039-4
481718 Fragile X, Fetal Analysis 21759-6 481709 General Comments 8262-8
481718 Fragile X, Fetal Analysis 21759-6 482030 MCC, Maternal Control 59266-7
481718 Fragile X, Fetal Analysis 21759-6 481710 Recommendations 55752-0
481718 Fragile X, Fetal Analysis 21759-6 481711 Additional ClinicalInformation 62385-0
481718 Fragile X, Fetal Analysis 21759-6 481712 Comments 8251-1
481718 Fragile X, Fetal Analysis 21759-6 481713 Methods/Limitations 49549-9
481718 Fragile X, Fetal Analysis 21759-6 481714 References 75608-0
481718 Fragile X, Fetal Analysis 21759-6 481715 Director Review/Release 72486-4
481718 Fragile X, Fetal Analysis 21759-6 481716 PDF 51969-4
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481702
Result Code NameEthnicity
UofM
Result LOINC42784-9
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481703
Result Code NameSpecimen Type
UofM
Result LOINC31208-2
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481704
Result Code NameGenetic Counselor
UofM
Result LOINC89993-0
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481705
Result Code NameIndication
UofM
Result LOINC42349-1
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481706
Result Code NameFetal ID
UofM
Result LOINC11951-1
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481707
Result Code NameResult:
UofM
Result LOINC21759-6
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481708
Result Code NameInterpretation
UofM
Result LOINC53039-4
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481709
Result Code NameGeneral Comments
UofM
Result LOINC8262-8
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code482030
Result Code NameMCC, Maternal Control
UofM
Result LOINC59266-7
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481710
Result Code NameRecommendations
UofM
Result LOINC55752-0
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481711
Result Code NameAdditional ClinicalInformation
UofM
Result LOINC62385-0
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481712
Result Code NameComments
UofM
Result LOINC8251-1
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481713
Result Code NameMethods/Limitations
UofM
Result LOINC49549-9
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481714
Result Code NameReferences
UofM
Result LOINC75608-0
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481715
Result Code NameDirector Review/Release
UofM
Result LOINC72486-4
Order Code481718
Order Code NameFragile X, Fetal Analysis
Order Loinc21759-6
Result Code481716
Result Code NamePDF
UofM
Result LOINC51969-4