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Neonatal blood Aneuploidy screening - FISH 2 probes (13 & 21)
Blood
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No Fasting Required
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Chromosomal abnormality detection.
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Neonatal Blood Aneuploidy Screening - FISH 2 Probes (13 & 21)
- Why is it done?
- This test uses Fluorescence In Situ Hybridization (FISH) technology to detect chromosomal abnormalities, specifically trisomy 13 (Patau syndrome) and trisomy 21 (Down syndrome), in neonatal blood samples
- Provides rapid detection of numeric chromosome abnormalities using probe hybridization targeting chromosomes 13 and 21
- Ordered when newborn screening results are abnormal or when clinical signs suggestive of chromosomal disorders are present at birth
- Used as a confirmatory test following abnormal prenatal screening or positive newborn screening results
- Typically performed within the first days to weeks of life when aneuploidy is suspected
- Provides results faster than conventional cytogenetics (typically 24-48 hours) for urgent clinical decision-making
- Normal Range
- Normal Result: Two signals for chromosome 13 (2q13) and two signals for chromosome 21 (2q21)
- This represents the normal diploid number (two copies) of each chromosome
- Abnormal Result - Trisomy 13: Three signals for chromosome 13
- Abnormal Result - Trisomy 21: Three signals for chromosome 21
- Monosomy 13 or 21 (rare): Only one signal detected for the respective chromosome
- Units of Measurement: Number of fluorescent signals per chromosome (reported as numerical count per cell)
- Interpretation: Normal vs. Abnormal
- NORMAL = Euploid (correct number of chromosomes); No aneuploidy detected
- ABNORMAL = Aneuploid (incorrect number of chromosomes); Presence of additional chromosome material
- Interpretation
- Two Signals (2,2): Normal result; No aneuploidy detected for chromosomes 13 and 21; Child does not have trisomy 13 or 21 based on this test
- Three Signals for Chromosome 13 (3,2): Positive result indicating trisomy 13 (Patau syndrome); Three copies of chromosome 13 present
- Three Signals for Chromosome 21 (2,3): Positive result indicating trisomy 21 (Down syndrome); Three copies of chromosome 21 present
- Three Signals for Both (3,3): Positive result for both trisomy 13 and trisomy 21; Rare concurrent occurrence
- One Signal (1,2 or 2,1): May indicate monosomy (loss of chromosome material); Very rare and often incompatible with life
- Mosaic Pattern: Mixed population of cells with different signal patterns; May indicate mosaic trisomy (some cells affected, others normal)
- Factors Affecting Test Accuracy:
- Sample quality and cell viability; Contaminated or degraded samples may produce false results
- Low-level mosaicism may be missed if present in fewer than 10-15% of cells analyzed
- FISH only detects numerical abnormalities; Structural rearrangements not detected with 2-probe system
- Technical issues with probe hybridization or fluorescent signal visualization
- Clinical Significance:
- Positive results confirm chromosomal aneuploidy; Enables rapid clinical diagnosis and allows for immediate intervention and family counseling
- Negative results exclude trisomy 13 and 21 with high sensitivity and specificity for these specific chromosomes
- Results guide immediate medical management decisions regarding surgical interventions and therapeutic options
- Associated Organs
- Primary System Involved:
- Chromosomal/Genetic system (affects multiple organ systems globally)
- Trisomy 21 (Down Syndrome) - Associated Conditions:
- Cardiac: Congenital heart defects (AV canal defects, ventricular septal defects, atrial septal defects) occur in 40-50% of cases
- Gastrointestinal: Duodenal atresia, tracheoesophageal fistula, imperforate anus, hirschsprung disease
- Neurological/Developmental: Intellectual disability (moderate to severe), developmental delay, hypotonia
- Ophthalmologic: Refractive errors, cataracts, keratoconus
- Hematologic: Transient myeloproliferative disorder, increased leukemia risk
- Skeletal: Hypotonia, ligamentous laxity, short stature
- Trisomy 13 (Patau Syndrome) - Associated Conditions:
- Cardiac: Congenital heart defects (PDA, ASD, VSD, dextrocardia) in 80% of cases; Often severe
- Gastrointestinal: Omphalocele, gastroschisis, cleft palate/lip, micrognathia
- CNS: Severe intellectual disability, holoprosencephaly, microcephaly, seizures
- Ocular: Microphthalmia, colobomas, cataracts, cyclopia
- Renal: Polycystic kidneys, hydronephrosis, renal hypoplasia
- Skeletal: Polydactyly, limb abnormalities, low-set ears
- Genitourinary: Hypospadias, cryptorchidism
- Potential Complications:
- Trisomy 13: High mortality in infancy (median survival 7-10 days without intervention); Severe multi-organ involvement often incompatible with survival beyond first year
- Trisomy 21: Generally compatible with life but significant medical burden; Increased risk of infections, hearing loss, thyroid disease
- Follow-up Tests
- Confirmatory Testing:
- Conventional Cytogenetics (Karyotype): Gold standard for confirmation; Complete chromosome analysis; Results typically available in 5-10 days
- Microarray (Array-CGH): Detects copy number variations; Identifies mosaic aneuploidy; Can detect unbalanced structural rearrangements
- Clinical Assessment and Organ-Specific Evaluation:
- Echocardiography: Essential for detecting cardiac abnormalities; Identify structural heart defects; Assess cardiac function
- Abdominal Ultrasound: Evaluate for gastrointestinal malformations; Assess renal anatomy; Screen for other visceral abnormalities
- Cranial Ultrasound or MRI: Evaluate for CNS malformations; Assess brain anatomy; Rule out holoprosencephaly
- Ophthalmology Exam: Assess for ocular abnormalities; Screen for cataracts; Evaluate vision
- Laboratory Tests:
- Complete Blood Count (CBC): Screen for anemia; Assess for transient myeloproliferative disorder
- Thyroid Function Tests (TSH, Free T4): Screen for congenital hypothyroidism (increased risk in Down syndrome)
- Metabolic Screening: Part of expanded newborn screening panel
- Genetic Counseling:
- Recommended for all positive results; Provides recurrence risk assessment; Discusses inheritance patterns and family implications
- Parental chromosomal analysis: Indicated if structural abnormalities suspected
- Monitoring Frequency:
- Immediate: Urgent cardiology and pediatric subspecialty consultations if positive result
- Short-term: Diagnostic imaging studies within first week of life
- Ongoing: Regular developmental monitoring, periodic medical evaluations, screening for age-appropriate complications
- Fasting Required?
- No fasting required
- This is a blood-based test that analyzes chromosomal material; Nutritional status and fasting state do not affect test accuracy
- Sample Collection:
- Blood sample typically collected via heel prick (newborn screening card) or venipuncture
- Best collected on filtered paper cards or in EDTA tube depending on laboratory requirements
- Timing Considerations:
- Test can be performed at any time; No need to wait for feeding times
- Typically performed between 24-48 hours of life as part of newborn screening protocol
- Special Instructions:
- Ensure adequate blood volume collected on screening card to avoid false results from inadequate cellular material
- Allow dried blood spots to dry completely before packaging (if using screening card method)
- No medications need to be held; Test accuracy not affected by routine neonatal medications
- Ensure proper sample labeling and chain of custody documentation
- Transport samples promptly to laboratory per institutional protocol to maintain cell viability
How our test process works!
