Lab Profiles UPDATED




Congenital Hypothyroidism
 
Condition: Congenital Hypothyroidism

A disorder of the thyroid gland which, if undetected, can lead to deafness or mental retardation. Found in 1 in every ~4,000 children in the US, detection and treatment usually allows a normal life for the child in question.

More technical information from the Mountain States Genetic Network:

Congenital hypothyroidism is one of the most common conditions detected by newborn screening, with an incidence rate of 1:4,000. Congenital hypothyroidism is caused by inadequate production of thyroid hormone. Thyroid hormone is important for normal function of all of the body's organs and is essential for normal brain development.

The most common etiologies are total or partial failure of the thyroid gland to develop (aplasia or hypoplasia), or its development in an abnormal location (an ectopic gland). Less commonly, hypothyroidism is induced by medications (antithyroid drugs or excess iodine) in the mother or is due to an inherited inability to manufacture thyroid hormone.

Deficiency of thyroid hormone in an infant causes mental retardation if it is not diagnosed and treated early in life. Most infants with congenital hypothyroidism appear to be clinically normal until three months of age, by which time brain development may be impaired.

Diagnosis
Laboratory test results are the only reliable means of diagnosing congenital hypothyroidism in the newborn infant. Some of the more commonly described clinical findings -- jaundice, constipation, lethargy, feeding problems, a large tongue, puffy face, distended abdomen, umbilical hernia -- are non-specific for congenital hypothyroidism, are found in fewer than 30% of neonates with congenital hypothyroidism, and may be present in infants without the condition. Therefore, in the newborn, clinical signs and symptoms are not reliable indicators of congenital hypothyroidism.

Laboratory Tests
All of the states in our region screen for congenital hypothyroidism. All screening programs in our region employ a two-tiered approach in screening for hypothyroidism. All specimens are tested for thyroxine (T4). A subset of samples with the lowest T4 values (usually the lowest 10%) are further tested with a thyroid stimulating hormone (TSH) assay.
Congenital hypothyroidism screening results fall into the following categories: the T4 value can be normal or low; the TSH value can be normal, high, or "borderline" -- not normal, but only slightly elevated. Refer to the table on page 15 for the numerical values used in your state screening program.

The AAP guidelines offer the following basic recommendation for follow-up of an abnormal newborn screening test result for hypothyroidism.

Any infant with a low T4 level and TSH concentration greater than 40 mU/L is considered to have primary hypothyroidism until proved otherwise. Such infants should be examined immediately and have confirmatory serum tests done to verify the diagnosis. Treatment with replacement l-thyroxine should be initiated before the results of the confirmatory tests are available....In cases in which the screening TSH concentration is only slightly elevated... but less than 40 mU/L, another filter paper specimen should be obtained for a subsequent screening test.(2)
Contact your state screening program for their specific recommendations for follow-up of abnormal newborn screening test results for hypothyroidism.


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2American Academy of Pediatrics Newborn Screening for Congenital Hypothyroidism: Recommended Guidelines PEDIATRICS, Vol. 91, No. 6, June 1993, 1203.
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Screening Practice Considerations
Detection does not depend on nutritional factors. The majority of hypothyroid infants are detected on the first specimen even if it is collected within a few hours after birth. As is true with other conditions, a blood transfusion may alter the values; the newborn screening specimen should always be collected prior to a blood transfusion, regardless of the infant's age.
In the first 24 hours after birth, TSH values may be transiently elevated; the normal newborn demonstrates a TSH surge in the first hours of life as an adaptation to the extrauterine environment. The newborn screen should be collected as late as possible before discharge (but no later than 72 hours of age.)

In premature infants, there appears to be a physiological reduction in blood T4 levels. This is not due to TBG deficiency and the TSH levels are not usually elevated. These cases need special follow-up to ensure that the T4 levels rise to the normal range as the infant matures, as will occur in all normal cases.

Prompt confirmatory testing is required even if there is evidence to suggest that one of the situations associated with false positive screens is present (e.g., early specimen collection or prematurity). The presence of any of these does not exclude the possibility of disease.

A small percentage of cases of congenital hypothyroidism do not develop until after the first weeks of life. Therefore, as with other screening tests, in the presence of clinical symptoms, evaluation for congenital hypothyroidism should be performed despite normal newborn screening results.


Treatment
Treatment of congenital hypothyroidism is simple and effective. Thyroid hormone (Synthroid or Levothroid), in pill form, is crushed, mixed with food, and administered once daily. (Generic forms of levothyroxine sodium should never be used to treat hypothyroidism.)
T4 and TSH levels need to be monitored as the infant grows, and infants and children with hypothyroidism should undergo periodic developmental evaluation. The AAP recommends consultation with a pediatric endocrinologist to facilitate diagnostic evaluation and optimal management. The directory on page 43 lists endocrinology consultants for your state who can offer assistance with diagnosis and management of congenital hypothyroidism.


The purpose of newborn screening is to identify infants at risk and in need of more definitive testing. As with any laboratory test, both false negative and false positive results are possible. Screening test results are insufficient information on which to base diagnoses or treatment.