Chromosome Analysis, Blood

Chromosome Analysis, Blood

Synonym/acronym: N/A.

Common use

To test for suspected chromosomal disorders that result in birth defects such as Down’s syndrome.

Specimen

Whole blood (2 mL) collected in a green-top (sodium heparin) tube.

Normal findings

(Method: Tissue culture and microscopic analysis) No chromosomal abnormalities identified.

Description

Cytogenetics is a specialization within the area of genetics that includes chromosome analysis or karyotyping. Chromosome analysis or karyotyping involves comparison of test samples against normal chromosome patterns of number and structure. A normal karyotype consists of 22 pairs or autosomal chromosomes and one pair sex chromosomes, XX for female and XY for male. Variations in number or structure can be congenital or acquired. Variations can range from a small, single-gene mutation to abnormalities in an entire chromosome or set of chromosomes due to duplication, deletion, substitution, translocation, or other rearrangement. Molecular probe techniques are used to detect smaller, more subtle changes in chromosomes. Cells are incubated in culture media to increase the number of cells available for study and to allow for hybridization of the cellular DNA with fluorescent DNA probes in a technique called fluorescence in situ hybridization (FISH). The probes are designed to target areas of the chromosome known to correlate with genetic risk for a particular disease. When a suitable volume of hybridized sample is achieved, cell growth is chemically inhibited during the prophase and metaphase stages of mitosis (cell division), and cellular DNA is examined to detect fluorescence, which represents chromosomal abnormalities, in the targeted areas. Amniotic fluid, chorionic villus sampling, and cells from fetal tissue or products of conception can also be evaluated for chromosomal abnormalities.

This procedure is contraindicated for

  • high alertCircumstances where the parents are not emotionally capable of understanding the test results and managing the ramifications of the test results.

Indications

  • Evaluate conditions related to cryptorchidism, hypogonadism, primary amenorrhea, and infertility
  • Evaluate congenital anomaly, delayed development (physical or mental), mental retardation, and ambiguous sexual organs
  • Investigate the carrier status of patients or relatives with known genetic abnormalities
  • Investigate the cause of still birth or multiple miscarriages
  • Investigate types of solid tumor or hematologic malignancies
  • Provide prenatal care or genetic counseling

Potential diagnosis

The following tables list some common genetic defects.
SyndromeAutosomal Chromosome DefectFeatures
AnglemanDeletion 15q11–q13Developmental delays (physical growth, communication, and motor skills); hyperactive behavior; overall happy demeanor with frequent laughter and hand-flapping actions; fascination with water
Beckwith-WiedemannDuplication 11p15Macroglossia, omphalocele, earlobe creases
BloomMutations of BLM, 15 Birth weight and length are below normal and stature remains below normal to adulthood; skin changes in response to sun exposure; increased risk of cancers which develop early in life; high-pitched voice; disctinctive facial features (long, narrow face with a small jaw; large nose and ears)
CanavanMutations of ASPA, 17p13.3 Developmental delays that become obvious at 3 to 5 months of age; hypotonia that contributes to inability to roll over, sit upright, or swallow; macrocephaly; and intellectual disability
Cat’s eyeTrisomy 2q11Anal atresia, coloboma
Cri du chatDeletion 5pCatlike cry, microcephaly, hypertelorism, intellectual disability, retrognathia
Cystic fibrosisMutations of CFTR, 7Impaired transport of chloride affects the movement of water in and out of the cells lining the lungs and pancreas. The result is production of thick mucus that obstructs airways and prevents normal function of the affected organs; life threatening, permanent lung damage
DiGeorgeDeletion 22q11.2There is a wide variety in the type and severity of problems associated with this syndrome of impaired development of body systems, most commonly included: cardiac abnormalities or defects, poor immune system function (hypothymic or absent thymus), cleft palate, hypoparathyroidism (low calcium); behavioral disorders; distinctive facial features (long face with downturned mouth, asymmetric face when crying, microcephaly, hooded eye lids, malformed ears)
DownTrisomy 21Epicanthal folds, simian crease of palm, flat nasal bridge, mental retardation, congenital heart disease
EdwardsTrisomy 18Micrognathia, clenched third/fourth fingers with the fifth finger overlapping, rocker-bottom feet, mental retardation, congenital heart disease
Gaucher’sMutations of GBA, 1Hepatomegaly and splenomegaly related to accumulation of lipids; anemia; thrombocytopenia; bone disease (bone pain, fractures, and arthritis).
Maple Syrup Mutations of BCKDHA, BCKDHB, DBT, and DLD, 19 Developmental delays; poor feeding; lethargy; distinctive maple syrup odor in urine
Miller-DiekerDeletion 17Lissencephaly (incomplete or absent development of the folds of the cerebrum); microcephaly; developmental delays, especially in growth; intellectual disability with seizures; difficulty feeding and failure to thrive; cardiac malformations
Niemann-PickChromosome 14q24.3 (type C2), 18q11.2 (type C1), 11p15.4–p15.1 (types A & B)Both types demonstrate symptoms that reflect abnormalities in liver and lung function; blood tests show hyperlipidemia (cholesterol and other fats) and thrombocytopenia
Pallister-KillianTrisomy 12pPsychomotor delay, sparse anterior scalp hair, micrognathia, hypotonia
PatauTrisomy 13Microcephaly, cleft palate or lip, polydactyly, mental retardation, congenital heart disease
Prader-WilliDeletion 15q11–q13Delayed development; distinctive facial features (narrow forehead, almond-shaped eyes, triangular-shaped mouth, diminished stature with small hands and feet); hypotonia; childhood development of an insatiable appetite, hyperphagia, and obesity; mild to moderate intellectual disability; behavioral problems (outbursts of anger and compulsive behavior such as picking at the skin)
Smith-MagenisDeletion 17p11.2 The major features of this condition include mild to moderate intellectual disability, delayed speech and language skills, distinctive facial features, sleep disturbances, and behavioral problems
Tay-SachsMutations of HEXA, 15q24.1Normal development until age 3 to 6 mo when development slows and hypotonia affects motor skills such as ability to turn over, sit upright, and crawl; exaggerated startle reaction to loud noises; seizures; eventual loss of vision (cherry red spot upon eye exam is characteristic) and hearing; intellectual disability
WarkamMosaic trisomy 8Malformed ears, bulbous nose, deep palm creases, absent or hypoplastic patellae
Wolf-HirschhornDeletion 4p16.3Microcephaly, growth retardation, mental retardation, carp mouth
SyndromeSex-Chromosome DefectFeatures
Fragile X Xq27.3Intellectual disability; autism and autism spectrum disorders
XYY47,XYYTall, increased risk of behavior problems
Klinefelter47,XXYHypogonadism, infertility, underdeveloped secondary sex characteristics, learning disabilities
Rett Mutations of, Xq28Severe and progressive developmental problems related to brain functions such as speech, motor and intelligence begin after 6 to 18 mo of normal growth; brain disorder almost exclusively affecting females; slower than normal physical growth; microcephaly; meaningful use of hands is lost in early childhood and replaced by repetitive random hand motions such as clapping or wringing.
Triple X47,XXXIncreased risk of infertility and learning disabilities
Ullrich-Turner45,XShort, gonadal dysgenesis, webbed neck, low posterior hairline, renal and cardiovascular abnormalities

Critical findings

    N/A

Interfering factors

    N/A

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in identification of potential birth defects.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s reproductive system, family history of known or suspected genetic disorders, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Recognize anxiety related to test results, and be supportive of the sensitive nature of the testing. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient regarding access to counseling services.
  • Social and Cultural Considerations: Encourage the family to seek counseling if they are contemplating pregnancy termination or to seek genetic counseling if a chromosomal abnormality is determined. Decisions regarding elective abortion should occur in the presence of both parents. Provide a nonjudgmental, nonthreatening atmosphere for discussing the risks and difficulties of delivering and raising a developmentally challenged infant, as well as exploring other options (termination of pregnancy or adoption). It is also important to discuss feelings the mother and father may experience (e.g., guilt, depression, anger) if fetal abnormalities are detected. Educate the patient and family regarding access to counseling services, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor changes in health status and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include α1-fetoprotein, amniotic fluid analysis, biopsy chorionic villus, newborn screening, and US biophysical profile obstetric.
  • Refer to the Reproductive System table at the end of the book for related tests by body system.
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