Investigations
1st investigations to order
chromosomal karyotype
Test
Indicated when Down's syndrome is suspected. Translocation results require testing the parents to determine future recurrence risks.
Standard trisomy 21 (extra chromosome 21) is caused by chromosome non-disjunction and occurs in 95% of cases. In about 4% to 5% trisomy results from a chromosome translocation, and the remaining 1% are mosaic with a combination of normal and trisomic cells.[5]
Result
trisomy 21, Robertsonian translocation, or mosaicism
FBC with differential
Test
Should be ordered within 3 days of birth to assess for haematological abnormalities such as transient abnormal myelopoiesis and polycythemia.[17]
Result
normal or haematologic abnormalities
echocardiogram
hearing test
Test
In the UK, hearing tests are conducted within the first 4-5 weeks of life.[32] Hearing screen is required in all newborns in the US. Requirements may vary internationally; please consult local guidance.
Objective tests such as brainstem auditory evoked response or otoacoustic emission may be appropriate.[17]
If the newborn does not pass the screening tests, refer to an otolaryngologist to assess for middle-ear abnormality.[17]
Tympanometry may be required if the tympanic membrane is not visualised.[17]
If it is confirmed that the newborn is deaf or hard of hearing, referral to early intervention should be made within 48 hours.[17]
Result
normal or mild to profound hearing loss
thyroid function tests
Test
In the UK, screening for congenital hypothyroidism is conducted as part of the newborn blood spot screening programme.[31] Thyroid function test is required in all newborns in the US. Requirements may vary internationally; please consult local guidance.
Both thyroid-stimulating hormone (TSH) and free thyroxine (T4) should be measured, as congenital hypothyroidism can be missed if only T4 is measured at newborn screening.[17]
A significant number of children with Down's syndrome may have subclinical hypothyroidism, which presents as normal T4 with mildly elevated TSH.[17]
Discuss management with a paediatric endocrinologist if there are TSH or T4 abnormalities.[17]
Result
normal; normal T4 with mildly elevated TSH; or low T4 with elevated TSH
vision examination
Test
Should be done in the newborn period because 4% of children with Down's syndrome are born with congenital cataracts.[5] Nasolacrimal duct may be obstructed as a complication of mid-face hypoplasia, but it improves with age.
If lacrimal duct obstruction is present, refer for evaluation for surgical repair of the drainage system if not resolved by 9-12 months of age.[17]
Other abnormalities include strabismus (23% to 44%), accommodative esotropia, myopia, hyperopia, and blepharitis.[35]
Result
variable abnormalities or normal
Investigations to consider
abdominal x-ray
Test
Infants with Down's syndrome (DS) may be born with a gastrointestinal (GI) defect such as duodenal or anal stenosis, or duodenal or anal atresia (5% to 12%).[17][30] Should be obtained in any newborn with DS presenting with vomiting, abdominal distention, or delay in stool passage.
Result
normal or congenital GI anomalies
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