Congenital Hypothyroidism
Congenital hypothyroidism (CH) is caused by a deficiency in the circulating thyroid hormone thyroxine. Left untreated, this congenital deficiency of thyroid hormone can result in mental retardation and stunted growth. Affected newborns may appear normal up to three months of age. If detected early and maintained on treatment (hormone replacement medication), infants with CH should have normal growth and development.
Prevalence: 1:2600 in Missouri
Analyte Measured: Thyroxine (T4) and Thyrotropin (TSH)
Reporting Ranges: T4 values of 6 ug/dL or less are considered to be “decreased”
TSH ranges are age dependent:
Age (hrs) |
Normal |
Borderline Risk |
High Risk |
< 24 |
0 - 29 ulU/mL |
30 - 59 ulU/mL |
60 ulU/mL |
> 24 |
0 - 24 ulU/mL |
25 - 49 ulU/mL |
50 ulU/mL |
At birth, there is a sharp increase in T4, which peaks at about 24 hours post partum and plateaus at about 48 hours of life. T4 levels begin to decline 3 – 5 days after birth. Decreased T4 levels are often seen in premature or sick infants and should be monitored closely. A few causes of decreased T4 levels and normal TSH levels are prematurity, low birth weight, illness, hypoproteinemia, thyroxine binding deficiency (TBG), and secondary – tertiary hypothyroidism. Delayed onset hypothyroidism should also be considered. Elevated TSH levels, in the Borderline Risk or High Risk range, may be detected when the sample is collected in the first 24 hours of life due to the “normal” after birth TSH surge. TSH levels should return to normal levels within 24 – 48 hours following birth. Typically in thyroid failure, the T4 remains decreased and TSH increased with an intact pituitary - hypothalmic feedback mechanism. All abnormal results need to be investigated by further testing.
Feeding Effect: None
Timing Effect: Elevated TSH results may occur if sample is collected before 24 hrs of age
Confirmation: (see table below)
Borderline Risk TSH and/or Decreased T4 results
|
Repeat newborn screening or do serum testing |
Repeat Borderline Risk TSH |
Promptly do serum T4 and TSH testing |
High Risk TSH |
Promptly do diagnostic thyroid serum testing, consult with pediatric endocrinologist. (If the elevated TSH is a probable “after birth surge” from an early collection time, then a repeat newborn screening may be done.) |
Treatment: Oral intake of thyroxine replacement medication. Consultation with a pediatric endocrinologist is recommended.
Comment: Newborn screening can detect congenital hypothyroidism with a high degree of accuracy, but the physician should remain alert to clinical symptoms in older infants despite normal newborn screening results. Delayed hypothyroidism and other forms of hypothyroidism can develop in the weeks after birth. Repeat the test if any doubt exists and be sure to follow up on all abnormal screening results.
Interpretation of Initial Newborn Screening Results for Congenital Hypothyroidism:
Screen Results |
Probable Cause |
Actions |
Follow Up |
T4 DECREASED,
TSH HIGH RISK |
Primary Hypothyroidism
Maternal Antibodies
Maternal Medications (PTU)
False Positive, TSH surge |
Lab will contact physician of record by phone (or other health care provider if physician unavailable), results faxed and mailed to physician. |
Diagnostic thyroid serum testing & consult with pediatric endocrinologist recommended. |
T4 NORMAL,
TSH HIGH RISK |
Hypothyroidism possible
False positive, TSH surge
Maternal Medications (PTU)
Maternal Antibodies |
Lab will contact physician of record by phone (or other health care provider if physician unavailable), results faxed and mailed to physician. |
If less than 24 hrs of age, repeat screen or do serum levels. Otherwise, do serum testing. Consult with pediatric endocrinologist recommended. |
T4 DECREASED, TSH NORMAL
T4 DECREASED, TSH BORDERLINE RISK |
Hypothyroidism possible
Pituitary/hypothalamic disorder
Secondary hypothyroidism
Prematurity
TGB deficiency
False Positive, TSH surge |
Very low T4 results are faxed to NICU or physician's office. Mailed results follow. |
Close clinical follow up is recommended. Rescreening, serum or diagnostic testing should be done to determine cause of low T4. |
T4 NORMAL
TSH BORDERLINE RISK* |
False Positive, TSH surge
Possible hypothyroidism
Maternal antibodies or medication
Other illness, prematurity |
Result faxed to physician of records. Mailed results follow. |
Repeat screen,
or do serum testing. |
* Repeat Borderline Risk TSH results should be followed up with diagnostic serum testing.
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