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Prenatal Spinal Muscular Atrophy (SMA) Testing

CPT: 81329
81401
81329
Updated on 11/18/2020
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Synonyms

  • Arthron-Ryposis Multiplex Congenita (Prental SMA)
  • Congenital Axonal Neurotherapy
  • Dubowitz Disease (SMA type II)
  • Kugelberg-Welander Disease (SMA type III)
  • SMA
  • SMN1 Copy-Number Analysis
  • Werdnig-Hoffman Disease (SMA type I)

Special Instructions

For prenatal/fetal testing only.

Testing referred to Integrated Genetics. To speak to a laboratory genetic coordinator before collecting specimens, LabCorp Clients, call 800-345-4363; Integrated Genetics clients, call 800-848-4436.

In some circumstances, specimens from other family members may be required. All prenatal specimens (including cord blood) must be accompanied by a maternal blood or mouthwash specimen for analysis of the specimen for possible maternal cell contamination. Cultures are required for prenatal SMA testing.


Related Information


Specimen Requirements


Specimen

Cultured amniotic fluid, or cultured chorionic villus (CVS) cells are required for testing.

Direct specimen can be submitted but a culture fee may be included. Submission of maternal blood is required for analysis of maternal cell contamination (MCC). MCC should be ordered on a separate requisition using test code 511402, Maternal Cell Contamination. Cultures are required for prenatal SMA testing.


Volume

Amniotic fluid: One T-25 flask of confluent cells. CVS: One T-25 flask of confluent cells. If cultured at another facility please maintain back-up cultures.


Container

Amniotic fluid: T-25 flasks

CVS: T-25 flasks


Collection

Amniotic fluid: Discard first 2 mL; then 15 mL amniotic fluid in 15 mL orange-top polypropylene tube. If cultured at another facility: 1 T-25 flask of confluent cells.


Storage Instructions

Maintain specimen at room temperature.


Causes for Rejection

Frozen or hemolyzed specimen; quantity not sufficient for analysis


Test Details


Use

Prenatal diagnosis for at-risk pregnancies, when both parents are carriers or when severe joint contractures are found on fetal ultrasound.

If prenatal diagnosis testing indicated an affected fetus (a 0 SMN1 copy number result), testing will reflex to SMN2 copy number analysis. SMN2, an adjacent gene to SMN1, also encodes low levels of SMN protein. Therefore, an increased SMN2 copy number (3+) may reduce disease severity among affected patients.


Limitations

This copy number analysis does not detect carriers of SMA as a result of either two (or very rarely three) copies of the SMN1 gene on one chromosome False-positive results or false-negative results may occur for reasons that include genetic variants, blood transfusions, bone marrow transplantation, erroneous representation of family relationships, or contamination of a fetal sample with maternal cells.


Methodology

After DNA is isolated, exon 7 of the SMN1 gene and internal standard reference genes are amplified by real-time polymerase chain reaction (PCR). A mathematical algorithm calculates SMN1 copy numbers of 0, 1, 2 or 3 with statistical confidence. To rule out the presence of sequence variants that could interfere with analysis and interpretation, sequence analysis of primer and probe binding sites is performed for postnatal samples with one copy of SMN1 and for all fetal samples. Reflex testing to SMN2 copy number analysis is performed for affected fetus with 0 copies of SMN1.


LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
452140 Prenatal SMN1 Copy Number 450001 Genetic Counselor: 89993-0
452140 Prenatal SMN1 Copy Number 450002 Client Specimen ID: 48767-8
452140 Prenatal SMN1 Copy Number 450003 Specimen Type: 31208-2
452140 Prenatal SMN1 Copy Number 450004 Specimen(s) Received: 74384-9
452140 Prenatal SMN1 Copy Number 450005 Clinical Data: 42349-1
452140 Prenatal SMN1 Copy Number 450006 Ethnicity: 42784-9
452140 Prenatal SMN1 Copy Number 450007 SMA Results: 41053-0
452140 Prenatal SMN1 Copy Number 450008 SMA Interpretation: 35462-1
452140 Prenatal SMN1 Copy Number 450009 Comments: 48767-8
452140 Prenatal SMN1 Copy Number 450111 Carrier Detection Rate: N/A
452140 Prenatal SMN1 Copy Number 450011 Method/Limitations: 49549-9
452140 Prenatal SMN1 Copy Number 450012 References: 69549-4
452140 Prenatal SMN1 Copy Number 450013 Disclaimer: 62364-5
452140 Prenatal SMN1 Copy Number 450014 Electronically Signed by: N/A
452140 Prenatal SMN1 Copy Number 450015 SMN1 Copy Number Analysis PDF 51969-4
452140 Prenatal SMN1 Copy Number 452141 SMA Results: 41053-0
Reflex Table for SMA Results:
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 451790 SMN2 Copy Number Reflex 451788 SMN2 Copy Number Reflex 54449-4

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The LOINC® codes are copyright © 1994-2020, Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee. Permission is granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the LOINC® codes for any commercial or non-commercial purpose, subject to the terms under the license agreement found at https://loinc.org/license/. Additional information regarding LOINC® codes can be found at LOINC.org, including the LOINC Manual, which can be downloaded at LOINC.org/downloads/files/LOINCManual.pdf