Test ID: ZYG
Zygosity Testing (Multiple Births)
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
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
Determining genetic risk for an individual whose twin/triplet is affected with a genetic disorder for which a specific genetic test is not available (or such testing is uninformative)
Assessment of risks prenatally when 1 fetus of multiples is known to be affected by a specific disorder
Organ or bone marrow transplantation compatibility testing
Familial/parental interest
Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request
DNA from twins and their parents is used to determine if the twins are identical or fraternal.
Reflex Tests Lists test(s) that may or may not be performed, at an additional charge, depending on the result and interpretation of the initial test(s)
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| FBC | Fibroblast Culture for Genetic Test | Yes | No |
| AFC | Amniotic Fluid Culture/Genetic Test | Yes | No |
Testing Algorithm Delineates situation(s) when tests are added to the initial order. This includes reflex and additional tests.
For prenatal specimens only: If amniotic fluid (non-confluent cultured cells) is received, amniotic fluid culture/genetic test will be added and charged separately. If chorionic villus specimen (non-confluent cultured cells) is received, fibroblast culture for genetic test will be added and charged separately.
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
Polymerase chain reaction (PCR)/microsatellite markers are used to provide a genotype for multiples and their parents to determine if siblings are monozygotic twins.
(PCR is utilized pursuant to a license agreement with Roche Molecular Systems, Inc.)
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
Multiple Births
Triplets
Twins
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.
Forms:
1. Molecular Genetics-Congenital Inherited Diseases Patient Information Sheet (Supply T521) in Special Instructions
2. 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 Molecular Genetics Request Form (Supply T245) with the specimen.
A blood specimen from both parents, in addition to a specimen from each multiple, is required. Each specimen will be charged separately.
Specimen must arrive within 96 hours of collection.
Submit only 1 of the following specimens:
Specimen Type: Whole blood
Container/Tube: Lavender top (EDTA) or yellow top (ACD)
Specimen Volume: 3 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Send specimen in original tube.
Specimen Stability Information: Ambient (preferred)/Refrigerated
Due to the complexity of prenatal testing, consultation with the laboratory is required for all prenatal testing. Prenatal specimens can be sent Monday through Thursday and must be received by 5 p.m. CST on Friday in order to be processed appropriately. All prenatal specimens must be accompanied by a maternal blood specimen. Order MCC/88636 Maternal Cell Contamination, Molecular Analysis on both the prenatal and the maternal specimens.
Specimen Type: Amniotic fluid
Container/Tube: Amniotic fluid container
Specimen Volume: 20 mL
Specimen Stability Information: Refrigerated (preferred)/Ambient
Specimen Type: Chorionic villi
Container/Tube: 15-mL tube containing 15 mL of transport media
Specimen Volume: 20 mg
Specimen Stability Information: Refrigerated
Acceptable:
Specimen Type: Confluent cultured cells
Container/Tube: T-25 flask
Specimen Volume: 2 flasks
Collection Instructions: Submit confluent cultured cells from another laboratory.
Specimen Stability Information: Ambient (preferred)/Refrigerated
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 |
|---|---|---|
| Varies | Varies | |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Approximately 30% of twins are monozygotic (identical) while 70% are dizygotic (nonidentical or fraternal). Monozygotic twins originate from a single egg, and by definition have identical DNA markers throughout their genomes. Dizygotic twins, on the other hand, inherit their genetic complement independently from each parent and are no more likely to have genetic material in common than are any other full siblings.
To date, literally thousands of polymorphic DNA markers have been identified. DNA markers are regions of DNA that display normal variability in the type or the number of nucleotide bases at a given location. One particular class of repetitive DNA that exhibits marked variability is microsatellites. With the use of such markers, it is possible to distinguish 1 individual from another because of differences detected at these polymorphic loci. Utilizing PCR followed by gel electrophoresis, the genotypes of a set of twins (triplets, etc.) are derived from the analysis of multiple markers. This genotype is compared to those of their parents to determine if the children are mono- or dizygotic. Any differences detected between siblings' microsatellite markers indicate dizygosity.
Many disorders are known to occur on a genetic basis though the genes have not been identified for all of them. If 1 member of a set of twins is diagnosed with a genetic disorder, determination of zygosity, in addition to other testing, may provide additional information regarding risk assessment of unaffected individuals. In addition, zygosity can be useful when evaluating for twin-twin transfusion syndrome during pregnancy or as part of a pre organ transplant workup for situations where 1 twin is donating an organ to another twin.
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.
An interpretive report will be provided.
Interpretation Provides information to assist in interpretation of the test results
An interpretive report will be provided.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in our interpretation of results may occur if information given is inaccurate or incomplete.
This test will detect nonpaternity.
A previous bone marrow transplant from an allogenic donor will interfere with testing. Call Mayo Medical Laboratories for instructions for testing patients who have received a bone marrow transplant.
Availability of a specimen from all family members (multiples and parents) provides the most accurate results. If parental blood is not available, markers may not be informative.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Appleman Z, Manor M, Magal N, et al: Prenatal diagnosis of twin zygosity by DNA "fingerprint" analysis. Prenat Diagn 1994;14(4):307-309
2. Neitzel H, Digweed M, Nurnberg P, et al: Routine applications of DNA fingerprinting with the oligonucleotide probe (CAC)5/(GTG)5. Clin Genet 1991;39(2):97-103
Method Description Describes how the test is performed and provides a method-specific reference
PCR-based assays that recognize highly variable regions of human DNA are used to provide a genotype for multiples and their parents. The number of markers (microsatellites) used is determined on a case-by-case basis to ensure >99.9% predictive value. Generally, between 6 and 11 markers are used. Calculation of zygosity probability is made using Bayesian analysis. (Neitzel H, Digweed M, Nurnberg P, et al: Routine applications of DNA fingerprinting with the oligonucleotide probe [CAC]5/[GTG]5.Clin Genet 1991;39[2]:97-103)
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.
Monday; 10 a.m.
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.
81265 Comparative analysis using Short Tandem Repeat (STR) markers; patient and comparative specimen (eg, pre-transplant recipient and donor germline testing, post-transplant non-hematopoietic recipient germline [eg, buccal swab or other germline tissue sample] and donor testing, twin zygosity testing or maternal cell contamination of fetal cells
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 |
|---|---|---|
| 16684 | Specimen | 31208-2 |
| 16685 | Specimen ID | N/A |
| 16686 | Source | N/A |
| 16687 | Order Date | N/A |
| 16688 | Reason For Referral | 42349-1 |
| 16689 | Method | In Process |
| 16690 | Result | N/A |
| 16691 | Interpretation | 69047-9 |
| 16692 | Amendment | In Process |
| 16693 | Reviewed By: | N/A |
| 16694 | Release Date | N/A |
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