Constitutional Chromosome Analysis – Non Blood – Amniotic Fluid

CPT Code(s)

88235, 88269

Performed

Clinical & Molecular Cytogenetics Laboratory

Clinical Indication and Relevance

A chromosome analysis on amniotic fluid may be clinically significant to identify genetic conditions associated with indications such as, advanced maternal age (AMA), sonographic anomalies, suspicious for trisomy 13, 18 or 21, abnormal quad screen, abnormal MaterniT21, open neural tube defect (NTD), genetic abnormality carrier and previous child with chromosome abnormality.  It is also relevant in cases to confirm a chromosome diagnosis by FISH and MaterniT21.

Clinical Background

Chromosome analysis on amniotic fluid is a procedure to rapidly culture and harvest amniocytes (amniotic cells) from amniocentesis for prenatal diagnosis of genetic and de novo (new or not genetic) chromosomal disorders. This type of analysis detects changes in the chromosome modal number, most often the common aneuploidies, and within the chromosome structure. Changes due to chromosome structure are usually associated with deletions or additions due to parent carrier status.  Amniocytes are most viable when drawn by amniocentesis performed between 15- and 18-weeks’ gestation.

Methodology

Culture / Microscopy / Karyotype

Amniotic fluid samples are long term cultures set up using the in situ method.  If two tubes with fluid are received, two cultures are initiated, “A” and “B”. The cells are usually ready for harvest in about 7 days. Fifteen cells are counted and only one metaphase from each in situ colony is studied.  Usually 8 cells from “A” culture are counted with 3 analyzed and 7 cells from “B” culture is counted with 2 analyzed, for a minimum of 5 completely analyzed metaphases.  Abnormal cases may require analysis of additional cells which sometimes result in longer culturing time and turnaround time.

Specimen Collection / Handling Requirements

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

Minimum Specimen Requirements

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 35°C

Turnaround time

Final report in 7-10 days for 90% cases

Communication

The morphologic interpretation and correlation of results on all cases is performed by a board-certified doctoral level scientist (laboratory director). The final report identifies the chromosomal sex and modal chromosome number.  If abnormalities are present, they are explained in a paragraph which helps to clarify and correlate chromosomal findings with phenotype. Genetic counseling is recommended when chromosome aberrations, mosaic conditions, or unusual results are found, along with recommendation for further testing (i.e. microarray).  References are included in the report to help the referring physician with interpretation, which include books or journals that contain appropriate information.

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