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Chromosome Analysis and AFP with Reflex to AChE, Fetal Hgb, Amniotic Fluid

Test code(s) 14591

This is an outdated version of this FAQ. It was effective 06/20/2014 to 04/14/2016.

The current version is available here.

Question 1. Multiple fetal anomalies were detected by ultrasound in this pregnancy, but the chromosome analysis and AFP study were normal. Are there further studies that can be done to evaluate for a genetic disorder in the fetus?

Yes, there are other studies that may be appropriate. There are many causes for fetal anomalies, some of which are genetic. In the absence of clinical suspicion for a specific genetic disorder, a microarray analysis may be performed to detect subtle deletions and duplications (Chromosomal Microarray, Prenatal, ClariSure® Oligo-SNP,test code 90927). If clinical suspicion exists for a specific disorder, there may be other genetic testing available. Please contact 866-GENE-INFO to discuss the case with a genetic counselor and for information on adding additional testing.

Question 2. My patient has a personal or family history of a chromosome abnormality. Prenatal chromosome testing on the fetus was reported as normal. Does this result guarantee that the fetus has not inherited the abnormality?

No. Please call 866-GENE-INFO to discuss this case with a genetic counselor. We need to know the specific genetic abnormality in the family, so we can determine whether the test’s resolution was sufficient to detect the abnormality.

Question 3. What chromosome abnormalities does this assay rule out?

This assay can rule out:

  1. Trisomies such as trisomy 21 (Down syndrome), trisomy 18, and trisomy 13

  2. Sex chromosome abnormalities such as Turner syndrome (45,X) and Klinefelter syndrome (47,XXY)

  3. Most rearrangements, including Robertsonian translocations and inversions

  4. Marker chromosomes

  5. Mosaicism at or above 19% (at a 95% confidence level)

  6. Most microscopically visible structural abnormalities

Question 4. What additional defects might be detected?

In addition to chromosome abnormalities, this test can detect conditions associated with an elevated alpha fetoprotein (AFP). Such conditions include open neural tube defects, abdominal wall defects, Turner syndrome, esophageal and duodenal atresia, and congenital hydronephrosis.

Fetal blood contamination of the specimen can cause an elevated AFP; therefore, a fetal hemoglobin test is performed to rule out a false-positive result. An acetylcholinesterase test is also performed as further confirmation of the elevated AFP. Acetylcholinesterase is associated with an open neural tube defect, anencephaly, gastroschisis, other ventral wall defects, Turner syndrome, teratoma, hypoplasia of heart and lung, fetal demise, and fetal hemoglobin contamination.

The fetal hemoglobin and the acetylcholinesterase tests are reported using separate CPT codes at an additional charge.

Question 5. What disorders cannot be detected by this assay?

This assay cannot detect:

  1. Subtle rearrangements, microduplications, and most microdeletion syndromes, including DiGeorge, Prader-Willi, Angelman, Williams, and Smith-Magenis syndromes

  2. Mosaicism below 19% (at a 95% confidence level)

  3. Fragile X syndrome

  4. Single gene disorders such as cystic fibrosis, Marfan syndrome, neurofibromatosis, etc.

Question 6. The report indicates that maternal cell contamination (MCC) cannot be ruled out. Is there a test that can be done to detect MCC?

Yes. The Maternal Cell Contamination Study, STR Analysis test (test code 10262X [10477X for NY]) can be performed if a maternal blood sample is submitted. If you are considering adding MCC studies to a completed prenatal case, please call 866-GENE-INFO to speak with a genetic counselor.

This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
Document FAQS.35 Version: 2
 
Version 2 effective 06/20/2014 to 04/14/2016
Version 0 effective 03/28/2012 to 11/18/2012