Test ID: SCE
Chromosome Analysis, Sister Chromatid Exchange (SCE) for Bloom Syndrome, Blood
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
As a diagnostic test for Bloom syndrome
Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request
Diagnostic testing for Bloom syndrome.
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
Cell Culture with Exposure to BrdU Prior to Harvest
Analysis of metaphases for statistical analysis of spontaneous sister chromatid exchange.
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
Chromosome, Sister Chromatid Exchange
Sister Chromatid Exchange
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 with each specimen. The laboratory will not reject testing if this information is not provided, but appropriate testing and interpretation may be compromised or delayed.
Container/Tube: Green top (sodium heparin)
Specimen Volume: 5 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Other anticoagulants are not recommended and are harmful to the viability of the cells.
Additional Information: Advise Express Mail or equivalent if not on courier service.
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.
2. If not ordering electronically, submit a Cytogenetics/AFP Congenital Disorders Request Form (Supply T238) with the specimen.
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 | Clotted blood |
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 |
|---|---|---|
| WB Sodium Heparin | Ambient (preferred) | |
| Refrigerated | ||
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Bloom syndrome is a genetic disorder associated with various congenital defects and predisposition to acute leukemia, pulmonary fibrosis, and Hodgkin lymphomas. Carcinoma also is commonly seen in these patients. Approximately one fourth to one half of patients develop some type of cancer with a mean age of 25 years at onset. The severity and age of onset of cancer varies among patients.
These patients often have prenatal or postnatal growth retardation, short stature, malar hypoplasia, telangiectatic erythema of the face and other regions, hypo- and hyperpigmentation, immune deficiencies, occasional mild mental retardation, infertility, and high-pitched voices.
Bloom syndrome is an autosomal recessive disorder caused by mutations in the BLM gene located at 15q26.1. While multiple mutations have been detected, the use of molecular testing to diagnose Bloom syndrome is limited in many ethnic groups. Patients with Bloom syndrome demonstrate a high frequency of chromosome abnormalities when their cells are cultured. Thus, cytogenetic studies can be helpful to establish a diagnosis.
Bloom syndrome results in 2 characteristic cytogenetic abnormalities. First, the cells are at increased risk for random breaks leading to fragments or exchanges between nonhomologous chromosomes. Second, cells in these patients have an increased frequency of sister chromatid exchanges (SCE: exchange of material between homologous chromosomes) of approximately 10-fold to 20-fold higher than average.
This test is diagnostic for Bloom syndrome. Carrier testing for Bloom syndrome is performed by different methodologies, so this test should not be ordered for that purpose.
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
The observation of a 10-fold or more increase in spontaneous sister chromatid exchange (SCE) relative to a control specimen and historical reference values is a diagnostic cytogenetic finding for Bloom syndrome.
Spontaneous SCE that is more than 10 times greater than the normal control could indicate exposure to a toxic substance. Therefore, clinical correlation is required.
A normal result does not rule out the possibility of birth defects, such as those caused by chromosomal abnormalities, molecular mutations, and environmental factors (ie, teratogen exposure). The test does not rule out other numeric or structural abnormalities. If a constitutional chromosome abnormality is suspected, a separate conventional cytogenetic study, CMS/8696 Chromosome Analysis, for Congenital Disorders, Blood should be requested.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test cannot be used to identify heterozygote carriers for Bloom syndrome and is not appropriate as part of a prenatal screening panel.
Interfering factors
Technical:
-Cell lysis caused by forcing the blood quickly through the needle
-Use of an improper anticoagulant (sodium heparin is best) or improperly mixing the blood with the anticoagulant
-Excessive transport time
-Inadequate amount of blood (we recommend 5 mL for adults and 2-5 mL for children)
-Exposure of the specimen to temperature extremes
Biological:
-T lymphocytes that do not respond to mitogens used to stimulate T cells to undergo mitosis (rare)
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Dicken CH, Dewald G, Gordon H: Sister chromatid exchanges in Bloom's syndrome. Arch Dermatol 1978:114;755-760
2. Kato H: Spontaneous sister chromatid exchanges detected by BUdR-labelling method. Nature 1974:251;70-72
3. Korenberg JR, Freedlender EF: Giemsa technique for the detection of sister chromatid exchanges. Chromosoma 1974:48;355-360
4. Latt SA: Microflurometric analysis of deoxyribonucleic acid replication kinetics and sister chromatid exchanges in human chromosomes. J Histochem Cytochem 1974:22;478-491
5. Perry P, Wolff S: New Giemsa method for the differential staining of sister chromatids. Nature 1974:251;156-158
Method Description Describes how the test is performed and provides a method-specific reference
A portion of the whole blood is transferred to a flask containing media and a cell mitogen. The cells are incubated for 96 hours at 37 degrees C. Twenty-four hours before harvest the cells are exposed to bromodeoxyuridine (BrdU) and protected from light. In the harvest process, the cells are exposed to colcemid and a hypotonic solution, and fixed with glacial acetic acid and methanol. Metaphase cells are dropped onto microscope slide and are treated with acridine orange. Twenty metaphases are examined for SCE using a fluorescence microscope system and documented by computer-based imaging. Mean frequency of SCE per metaphase is calculated and compared with SCE per metaphase from a parallel control. (Dicken CH, Dewald G, Gordon H: Sister chromatid exchanges in Bloom's syndrome. Arch Dermatol 1978;114:755-760)
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.
88230-Tissue culture for chromosome analysis
88245-Chromosome analysis for breakage syndromes
88291-Interpretation and report
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 |
|---|---|---|
| 15963 | Specimen | 31208-2 |
| 16320 | Specimen ID | N/A |
| 16778 | Source | N/A |
| 15964 | Order Date | N/A |
| CG382 | Reason For Referral | 42349-1 |
| 15968 | Method | In Process |
| 50474 | Banding Methods | 62359-5 |
| 15970 | Results | In Process |
| 15971 | Interpretation | 69965-2 |
| 15972 | Amendment | In Process |
| 15973 | Consultant | N/A |
| 15974 | Report Date | N/A |
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