Test ID: AF
Chromosome Analysis, Amniotic Fluid
NY State Approved 
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Prenatal diagnosis of chromosome abnormalities (trisomies, deletions, translocations, etc)
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
Method Name A short description of the method used to perform the test
Includes 2 banded karyograms, analysis of 15 or more metaphases, and other techniques when required. Results are usually confirmed in 15 or more colonies from 3 or more primary cultures.
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Down Syndrome
Karyotype, Amniotic Fluid
Prenatal Diagnosis
Trisomy 21
Amniotic Fluid, Chromosome Analysis
Prenatal Chromosomes, Amniotic Fluid
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Provide a reason for referral and gestational age with each specimen, and verify the specimen source. The laboratory will not reject testing if this information is not provided, but appropriate testing and interpretation may be compromised or delayed.
Portions of the specimen may be used for other tests such as measuring markers for neural tube defects (eg, AFPA/9950 Alpha-Fetoprotein, Amniotic Fluid), molecular genetic testing, biochemical testing, and FISH testing (including PAD/81424 Prenatal Aneuploidy Detection, FISH). If additional molecular genetic or biochemical genetic testing is needed, order AFC/80334 Amniotic Fluid Culture for Genetic Testing so that amniocyte cultures may be set up specifically for the use in these tests.
Forms:
1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (Supply T576) is available in Special Instructions.
3. If not ordering electronically, submit a Cytogenetics/AFP Congenital Disorders Request Form (Supply T238) with the specimen.
Advise Express Mail or equivalent if not on courier service.
Specimen Type: Amniotic fluid
Submission Container/Tube: Centrifuge tube
Specimen Volume: 20-25 mL
Collection Instructions:
1. Optimal timing for specimen collection is during 14 to 18 weeks of gestation, but specimens collected at other weeks of gestation are also accepted.
2. Discard the first 2 mL of amniotic fluid.
Additional Information:
1. Place the tube in a Styrofoam container (Supply T329). Fill remaining space with packing material.
2. Unavoidably, about 1% to 2% of mailed-in specimens are not viable. If the specimen does not grow in culture, you will be notified within 7 days of receipt.
3. Bloody specimens are undesirable.
Specimen Type: Fetal body fluid
Container/Tube: Sterile tube
Specimen Volume: Entire specimen
Additional Information:
1. Place the tube in a Styrofoam container (Supply T329). Fill remaining space with packing material.
2. If the specimen does not grow in culture, you will be notified within 7 days of receipt.
3. Clearly indicate on tube and paperwork that specimen is fetal body fluid.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | NA |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Amniotic Fld | Refrigerated (preferred) | |
| Ambient | ||
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Chromosomal abnormalities are the cause of a wide range of disorders associated with birth defects and congenital diseases. Many of these disorders can be diagnosed prenatally by analysis of amniocytes. Amniotic fluid can be safely collected after 12 weeks of gestation, although for optimal cell growth, collection from 14 to 18 weeks of gestation is preferred. This method permits diagnosis of chromosome abnormalities during the second trimester of pregnancy or later.
The most common reasons for cytogenetic studies for prenatal diagnosis include advanced maternal age, abnormal maternal serum screen, a previous child with a chromosome abnormality, abnormal fetal ultrasound, or a family history of a chromosome abnormality.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
46,XX or 46,XY. No apparent chromosome abnormality.
An interpretative report will be provided.
Interpretation Provides information to assist in interpretation of the test results
Cytogenetic studies on amniotic fluid are considered nearly 100% accurate for the detection of large fetal chromosome abnormalities. However, subtle or cryptic abnormalities involving microdeletions usually can be detected only with the use of targeted FISH testing.
Approximately 3% of amniotic fluid specimens analyzed are found to have chromosome abnormalities. Some of these chromosome abnormalities are balanced and may not be associated with birth defects.
A normal karyotype does not rule out the possibility of birth defects, such as those caused by submicroscopic cytogenetic abnormalities, molecular mutations, and other environmental factors (ie, teratogen exposure). For these reasons, clinicians should inform their patients of the technical limitations of chromosome analysis prior to performing the amniocentesis.
It is recommended that a qualified professional in Medical Genetics communicate all results to the patient.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Interfering factors
Technical:
-Improper syringes or transport vessels may be unsuitable to amniotic cells. Amniotic fluid should not be exposed to the syringe plunger tip for longer than a few seconds and fluid should be transferred to a transport (centrifuge) tube as soon as possible following collection.
-Transport time should not exceed 2 days.
-A bloody specimen may interfere with attempts to culture cells.
-Inadequate amount of fluid (we recommend 25 mL of fluid) may not permit adequate analysis.
-Improper packaging may result in broken, leaky, and contaminated specimen during transport.
-Exposure of the specimen to temperature extremes may kill cells and severely interferes with attempts to culture cells.
Biological:
-Contamination of the amniotic fluid by maternal cells can cause minor interpretive problems.
-False chromosome mosaicism may occur due to an artifact of culture.
-True mosaicism is rare and low levels may be missed due to statistical sampling error.
-Subtle structural chromosome abnormalities can occasionally be missed.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
Van Dyke DL, Roberson JR, Wiktor A: Chapter 31: Prenatal cytogenetic diagnosis. In Clinical Laboratory Medicine. Edited by KD McClatchey. Second edition, Philadelphia, Lippincott, Williams & Wilkins, 2002, pp 636-657
Method Description Describes how the test is performed and provides a method-specific reference
The specimen is centrifuged and the cell pellet is mixed with culture media, then split into 6 primary culture dishes and a T-flask to establish cultures. Cells are harvested after 5 to 7 days. In the harvest process, the cells are exposed to ethidium bromide, colcemid, and hypotonic solution, and fixed with glacial acetic acid and methanol. Metaphase cells are dropped onto microscope slides and are routinely stained by G-banding, but other staining methods may be employed as needed. Twenty metaphases from 15 colonies and 3 or more primary cultures usually are examined. In cases where true mosaicism is suspected, up to 30 colonies and up to 6 primary cultures may be analyzed. Minimal evidence for the presence of an abnormality is defined as 2 or more metaphases with the same structural abnormality or chromosome gain (trisomy), or 3 or more metaphases lacking the same chromosome. Five or more digitized images of metaphases are stored in computer-based imaging systems and karyograms are prepared from 2 or more representative metaphases.(Chang HC, Jones OW: Amniocentesis: cell culture of human amniotic fluid in a hormone supplement. Cold Springs Harb Conf Cell Prolif 1982;9:1187-1192; Hsu LY, Perlis TE: United States survey on chromosome mosaicism and pseudomosaicism in prenatal diagnosis. Prenat Diagn 1984;4:97-130; Peakman DC, Moreton MF, Corn BJ, Robinson A: Chromosomal mosaicism in amniotic fluid cell cultures. Am J Hum Genet 1979;31:149-155; Spurbeck JL, Carlson RO, Allen JE, Dewald GW: Culturing and robotic harvesting of bone marrow, lymph nodes, peripheral blood, fibroblasts, and solid tumors with in situ techniques. Cancer Genet Cytogenet 1988;32:59-66)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Samples processed Monday through Sunday. Results reported Monday through Friday, 8 a.m.-5 p.m. CST.
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
88235-Tissue culture for amniotic fluid or chorionic villus cells
88291-Interpretation and report
88299-Unlisted cytogenetic study (Refer to patient report to apply the appropriate CPT code below in place of this unlisted cytogenetic study CPT code)
Based on the total number of cells analyzed and counted, MML would recommend the following:
Chromosome analysis with 6-12 colonies, karyotypes with banding; CPT Codes 88269, 88280
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 16035 | Specimen | 62351-2 |
| 16326 | Specimen ID | N/A |
| G_744 | Source | N/A |
| 16036 | Order Date | N/A |
| G_750 | Reason For Referral | 42349-1 |
| 16040 | Method | In Process |
| 50460 | Banding Methods | 62359-5 |
| 16042 | Results | 33773-3 |
| 16043 | Interpretation | 69965-2 |
| 16044 | Amendment | In Process |
| 16045 | Consultant | N/A |
| 16046 | Report Date | N/A |
External
link
PDF
document
Excel
document
Word
document