RESUMO
OBJECTIVES: To determine the type and frequency of thyroid disorders detected in infants with low thyroxine (T4) and nonelevated thyroid-stimulating hormone (TSH) screening test results in the Northwest Regional Newborn Screening Program (NWRNSP) over the 20-year period from May 1975 to May 1995 and to determine the effect of follow-up of these infants on the overall recall rate. STUDY DESIGN: The NWRNSP requests a serum specimen in infants with an absolute T4 level < 38.6 nmol/L (< 3 mg/dl) and in infants with two filter paper T4 concentrations less than the 3%, regardless of the TSH concentration. We conducted a retrospective analysis of infants who were followed up because of low T4 and nonelevated TSH concentrations on newborn screening. To determine the effect of follow-up of infants with low T4 levels, nonelevated TSH concentrations on the recall rate, we selected 1 year (1994) for review. Serum sample requests were evaluated to determine the reason for the request. RESULTS: Over this 20-year period, the NWRNSP detected 450 infants with primary hypothyroidism among 1,747,805 infants screened (1:3,884). Of these, 416 were detected on the basis of low T4 levels and nonelevated TSH screening test results, whereas an additional 34 infants with primary hypothyroidism and 29 infants with hypopituitary hypothyroidism were detected as a result of follow-up of low T4 levels and nonelevated TSH screening test results. This included 25 infants with delayed TSH rise (1:67,226), 9 infants with mild hypothyroidism (TSH levels < 25 mU/L) (1:194,212), 29 infants with hypopituitary hypothyroidism (1:60,269), and 434 infants with T4-binding globulin deficiency (1:4,027). Excluding those with T4-binding globulin deficiency, the false-positive rate was 43.5:1. This compares with an overall false-positive rate of 12:1 for our screening program. CONCLUSION: Follow-up of infants with low T4 and nonelevated TSH concentration on screening led to the detection of 63 additional infants with hypothyroidism, for an overall frequency of 1:27,743. We believe this yield justifies continued follow-up of infants with low T4 levels, nonelevated (TSH) screening test results in our program.
Assuntos
Hipotireoidismo/diagnóstico , Triagem Neonatal , Testes de Função Tireóidea , Reações Falso-Positivas , Seguimentos , Humanos , Lactente , Recém-Nascido , Estudos Retrospectivos , Tireotropina , Tiroxina/sangueRESUMO
We examined the results of the Northwest Regional Screening Program (NWRSP) over its first 10 years to determine whether the detection of hypopituitary hypothyroidism is a justified advantage of the primary thyroxine (T4)-supplemental thyroid-stimulating hormone (TSH) screening strategy, and to determine whether all such infants will be detected by this screening approach. Between May 1975 and May 1985, the NWRSP screened 850,431 infants, detecting 192 infants with primary hypothyroidism (1:4429) and eight with hypopituitary hypothyroidism (1:106,304). In 11 additional infants, TSH deficiency, not detected by the screening program, was diagnosed on recognition of clinical features over the same period. Thyroid hormone treatment was begun in seven of the 11 infants prior to obtaining the screening sample results because of clinical symptoms of hypopituitarism, including hypoglycemia, persistent jaundice, microgenitalia, diabetes insipidus, midface hypoplasia, cleft lip or palate, or abnormalities of vision. The other four infants were not detected despite clinical features of hypopituitarism (in retrospect) and low serum T4 with TSH concentration below assay sensitivity on at least one screening sample. The most accurate assessment of total cases comes from Oregon, where all cases of congenital hypopituitarism are referred to our center; we estimate a frequency of 1:29,000. In our experience, a combination of newborn T4-supplemental TSH screening measurements and recognition of clinical features of hypopituitarism is the optimal strategy for detecting infants with congenital hypopituitary hypothyroidism.