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Newborn Screening for Congenital Hypothyroidism: Recommended Guidelines

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Newborn Screening for Congenital Hypothyroidism: Recommended Guidelines American Academy of Pediatrics American Thyroid Association Newborn Screening for Congenital Hypothyroidism: Recommended Guidelines During the past decade newborn screening for of identifying newborns with hyperthyroxinemia congenital hypothyroidism has become an impor- (1:20,000 to 40,000 newborns). tant health activity in most developed countries. On the other hand, this approach will miss in- These screening programs have not only benefited fants who have normal T4 values but elevated TSH patients and their families but also have produced values. Such infants are relatively commonplace in new information about the epidemiology, patho- European programs where initial screening is done physiology, diagnosis, and treatment of thyroid dis- by measurement of TSH. To identify such infants, ease in infancy and childhood. During this period the T4 concentration cutoff (for TSH testing) must of implementation and growth of the screening be increased well into the normal range. programs, a variety of issues and questions arose. Some of these have been resolved, and some have TSH not. The point has now been reached where colla- A majority of European and Japanese programs tion of the combined experiences of the North favor screening by means of primary TSH mea- American programs can address these issues. The surements, supplemented by T4 determinations on reader should understand that what follows reflects those infants with elevated TSH values. With this 0 current opinion and may require changes when the approach, infants with thyroxine-binding globulin results of the next decade of screening are reviewed. deficiency, hypo- or hyperthyroxinemia, or hypo- thalamic-pituitary hypothyroidism will be missed. SCREENING METHOD Until further advances are made in the state of the art of screening, the choice ofthe method should Thyroxine (T4) and Thyroid-Stimulating Hormone be based on the experience of the program, needs (TSH) of the population, and availability of resources. Most North American programs use a two-tiered Until T4 and TSH determinations can be done laboratory approach. An initial T4 measurement is practically on all infants, physicians should be followed by measurement of TSH in specimens with aware of potential limitations in each method of low T4 values. In addition to detecting infants with screening for congenital hypothyroidism. Even in primary hypothyroidism (low or low normal T4 level the absence of technical or human errors, statistical with elevated TSH value; prevalence 1:3,500 to information suggests that 6% to 12% of patients 4,500 newborns), this approach can also identify with infantile hypothyroidism will have normal infants with thyroxine-binding globulin deficiency screening hormonal concentrations regardless of and some with hypothalamic-pituitary hypothy- the type of approach used and can be missed by the roidism (low or low normal T4 level with normal screening programs. (Combinations of values lead- TSH value; prevalence 1:5,000 to 10,000 and ing to misses could be normal T4, high TSH; normal 1:50,000 to 150,000 newborns, respectively). Pro- T4, normal TSH; low T4, normal TSH). grams that quantify T4 values also have the option Quality Assurance The proliferation of new screening programs and The recommendations in this statement do not indicate an the expansion of older ones has underscored the exclusive course of treatment or procedure to be followed. Vari- need for clear guidelines for quality assurance. With ations, taking into account individual circumstances, may be this in mind, directors of newborn screening pro- 0 appropriate. PEDIATRICS (ISSN 0031 4005). Copyright © 1987 by the grams and physicians are advised to become famil- American Academy of Pediatrics. iar with the monograph, Legal Liability and Quality Downloaded from www.aappublications.org/news by guest on October 2, 2021 PEDIATRICS Vol. 80 No. 5 November 1 987 745 Assurance in Newborn Screening, Lori B. Andrews, heat. The blood should completely saturate the JD (ed), 1985, which can be obtained from the filter paper and be applied to one side only. Filter National Center for Education in Maternal and paper spots should not be handled, placed on wet Child Health, Georgetown University, 38th and R surfaces, or contaminated by coffee, milk, or other St, NW, Washington, DC 20057. substances. All of the foregoing have the potential o to invalidate the results regardless of the method THE SPECIMEN used. Every newborn infant should be tested before TEST RESULTS discharge from the nursery. Results from specimens obtained within the first 24 to 48 hours of life Normal T4 Values occasionally are falsely positive for primary hypo- thyroidism (using TSH as the primary screen) be- The normal range of T4 values and the cutoff cause of the elevated levels of TSH that occur level for TSH testing usually are established by the shortly after birth. However, screening before dis- individual program. Generally, the cutoff value var- charge is preferable to missing the diagnosis of ies from 1.5 to 2 SD below the mean of the normal hypothyroidism because of the lack of a clearly range. However, many programs have opted to use defined policy of responsibility for blood collection a tenth percentile cutoff. from infants discharged early. Because newborn Long-term follow-up for late-onset cases has not blood specimens are used for a variety of tests and been reported. Programs in which second speci- shared among different laboratories, every effort mens are obtained (4 to 6 weeks) have indicated should be made to collect adequate and sufficient that 10% of hypothyroid infants with T4 values in the normal range and elevated TSH values or with blood in the recommended manner (see Blood Col- kction on Filter Paper for Neonatal Screening Pro- initially low TSH values were missed during initial grams: Tentative Standard, NCCLS publication screening. Clearly, infantile hypothyroidism can LA4-T, Villanova, PA, National Committee for still develop even when the screening T4 value is Clinical Laboratory Standards, 1985). The recall of reported to be normal. Repeat testing should be an infant because of an unsatisfactory specimen done on serum during infancy whenever there is a causes needless delay in diagnosis and treatment of clinical suspicion of hypothyroidism or when there is a family history of thyroid disease in pregnancy a newborn with hypothyroidism. Although the test- 0 ing of an unsatisfactory specimen (because of in- or familial thyroid dyshormonogenesis. sufficient blood) can result in a false-negative TSH Low T4, Elevated TSH Values value, false-negative values can also result from human error in the processing of satisfactory spec- Any infant with a low T4 and TSH value greater imens or in erroneously reporting the results. than 40 U/mL of serum is considered to have It is highly desirable that the blood be collected primary hypothyroidism until proved otherwise. between three and six days, but there will be situ- Such infants should be examined immediately and ations when this is virtually impossible. In in- have confirmatory serum tests done to verify the stances such as home births, discharge before 24 diagnosis. Treatment with replacement 1-thyroxine hours, or a critically ill or premature neonate, blood should be initiated before the results of the con- should be obtained by seven days after birth. When firmatory tests are available. (Clinical management an infant is transferred to another hospital, the of infants with hypothyroidism is described below.) first hospital must indicate whether the specimen A small number of infants with abnormal screening has been collected. The second hospital should ob- values will have transient hypothyroidism as dem- tam a specimen if there is no proof that blood was onstrated by normal T4 and TSH values on the collected before the transfer. confirmatory (follow-up to screening) laboratory Mothers who have undergone treatment for thy- tests. Transient hypothyroidism frequently results roid disorders or who have a history of a previous from intrauterine exposure to antithyroid drugs child with goitrous or nongoitrous congenital hy- (including iodine), maternal antithyroid antibodies, pothyroidism should be identified during pregnancy or endemic iodine deficiency. Cases also have been to expedite the screening of the offspring. reported in association with pseudohypoparathy- Accurate screening results depend on good qual- roidism and prenatal or postnatal exposure to ex- ity blood spots. Specimens that are technically un- cess iodides (povidone iodine, iodinated contrast satisfactory or contain insufficient amounts of materials). The practice of using liberal quantities 0 blood should not be assayed. Blood samples should of iodine-containing solutions as disinfectants in be collected on approved filter paper forms, dried newborn nurseries should be balanced against the at room temperature, and not subjected to excessive potential for producing transient hypothyroidism. 746 CONGENITAL HYPOTHYROIDISMDownloaded from www.aappublications.org/news by guest on October 2, 2021 Idiopathic transient hypothyroidism and cases as- Serum TSH values in these infants increase during sociated with postnatal iodine exposure are 30 times the first few weeks of life to values characteristic more common among premature neonates. Other of primary hypothyroidism. It is important, there- features that suggest a transient condition are rel- fore, that screening be repeated on any infant in 0 atively modest elevations of TSH values (20 to 100 whom clinical signs of hypothyroidism appear. zU/mL), male sex, and a eutopic gland on radio- Based on experience, the prevalence of such cases isotope scanning. Because transient hypothyroid- is one in 50,000 to one in 100,000 newborns. ism will not be recognized in some infants, initial The possibility that such infants, plus those with treatment will be similar to that in any infant with elevated TSH values but normal T4 concentrations, permanent infantile hypothyroidism. For this rea- would be missed on initial screening has prompted son, it is important to determine at some later time a few programs to rescreen all newborns at 2 to 4 whether or not the hypothyroidism is permanent weeks of age.
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