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Test Code Billings Clinic: 8026 Chromosome Analysis, Fragile X, Blood

Performing Laboratory

Shodair Children's Hospital, Helena, Montana

Useful For

  • Confirmation of diagnosis in a patient with consistent signs and symptoms, especially males with a positive family history of mental retardation.
  • Testing is often used in a “screening” fashion since physical signs are subtle, and are difficult to recognize in affected females. Pregnant women with a family history of mental retardation in males may be suitable candidates for carrier testing.

Methodology

  • Patient DNA is amplified by PCR and CGG allele sizes determined by a high resolution laserinduced capillary fluorescence electrophoresis system.
  • Southern hybridization of probe StB12.3 to an EcoRI / EagI digest of genomic DNA detects larger expansions and assesses FMR-1 methylation.
  • Results are reported within 3 weeks or less of receipt of sample; expedited on request.
  • Based on Guidelines from the American College of Medical Genetics (ACMG, 1994), a comprehensive genetic evaluation of patients with mental retardation of unknown cause should include routine cytogenetic analysis as well as DNA analysis for Fragile X syndrome. Chromosome abnormalities have been identified as often as or more frequently than FMR-1 mutations in mentally retarded individuals referred for Fragile X testing.

Specimen Requirements

Specimen must arrive at Shodair Children’s Hospital within 24 hours of draw. Contact Billings Clinic Laboratory at 866-232-2522 to discuss the best specimen transport.

 

EDTA whole blood and sodium heparin whole blood are required for this test.

 

EDTA Whole Blood for Molecular Analysis

  • Draw a full, lavender-top (EDTA) tube, and send 10 mL of unprocessed EDTA whole blood.
  • Invert several times to mix blood.
  • Forward unprocessed whole blood promptly at ambient temperature only.
  • Specimen cannot be frozen.
  • Protect specimen from extreme temperatures.
  • When shipping, try to keep specimen as close to room temperature as possible.
  • Reason for referral plus relevant clinical and family information, date of birth, sex, and diagnosis are required on request form for processing and to provide correct interpretation of test results.
  • Label specimen appropriately (EDTA whole blood for molecular analysis).

Sodium Heparin Whole Blood for Cytogenetic Analysis

  • Draw a full, green-top (sodium heparin) tube, and send 5 mL of sodium heparin whole blood.
  • Invert several times to mix blood.
  • Forward unprocessed whole blood promptly at ambient temperature only.
  • Specimen cannot be frozen.
  • Protect specimen from extreme temperatures.
  • When shipping, try to keep specimen as close to room temperature as possible.
  • Reason for referral plus relevant clinical and family information, date of birth, sex, and diagnosis are required on request form for processing and to provide correct interpretation of test results.
  • Label specimen appropriately (sodium heparin whole blood for cytogenetic analysis).

Reject Due To

  • Clotted specimens
  • Frozen specimens

Reference Values

Reference values are included with patient’s report.

Day(s) Test Set Up

Daily

Test Classification and CPT Coding

83891 - Molecular diagnostics; isolation or extraction of highly purified nucleic acid, each nucleic acid type (ie, DNA or RNA)
83892 - Molecular diagnostics; enzymatic digestion, each enzyme treatment
83894 - Molecular diagnostics; separation by gel electrophoresis (eg, agarose, polyacrylamide), each nucleic acid preparation
83896 - Molecular diagnostics; nucleic acid probe, each
83897 - Molecular diagnostics; nucleic acid transfer (eg, Southern, Northern), each nucleic acid preparation
83898 - Molecular diagnostics; amplification, target, each nucleic acid sequence
83912 - Molecular diagnostics; interpretation and report