Neonatal thyroid-stimulating hormone level and perchlorate in drinking water.

BACKGROUND: The effect of perchlorate in drinking water on neonatal blood thyroid-stimulating hormone (thyrotropin; TSH) levels was examined for Las Vegas and Reno, Nevada. METHODS: The neonatal blood TSH levels in Las Vegas (with up to 15 microg/L (ppb) perchlorate in drinking water) and in Reno (with no perchlorate detected in the drinking water) from December 1998 to October 1999 were analyzed and compared. The study samples were from newborns in their first month of life (excluding the first day of life) with birth weights of 2, 500-4,500 g. A multivariate analysis of logarithmically transformed TSH levels was used to compare the mean TSH levels between Las Vegas and Reno newborns, with age and sex being controlled as potential confounders. RESULTS: This study of neonatal TSH levels in the first month of life found no effect from living in the areas with environmental perchlorate exposures of

Neonatal thyroxine level and perchlorate in drinking water.

Environmental contamination of drinking water has been observed for perchlorate, a chemical able to affect thyroid function. This study examines whether that exposure affected the thyroid function of newborns. Neonatal blood thyroxine (T4) levels for days 1 to 4 of life were compared for newborns from the city of Las Vegas, Nevada, which has perchlorate in its drinking water, and those from the city of Reno, Nevada, which does not (detection limit, 4 micrograms/L [ppb]). This study is based on blood T4 analyses from more than 23,000 newborns in these two cities during the period April 1998 through June 1999. No difference was found in the mean blood T4 levels of the newborns from these two cities. Drinking water perchlorate levels measured monthly for Las Vegas ranged during this study period from non-detectable for 8 months to levels of 9 to 15 ppb for 7 months. Temporal differences in mean T4 level were noted in both cities but were unrelated to the perchlorate exposure. This study was sufficiently sensitive to detect the effects of gender, birth weight, and the day of life on which the blood sample was taken on the neonatal T4 level, but it detected no effect from environmental exposures to perchlorate that ranged up to 15 micrograms/L (ppb).

Follow-up of newborns with low thyroxine and nonelevated thyroid-stimulating hormone-screening concentrations: results of the 20-year experience in the Northwest Regional Newborn Screening Program.

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.

Detection of congenital hypopituitary hypothyroidism: ten-year experience in the Northwest Regional Screening Program.

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.

Screening for congenital hypothyroidism with specimen collection at two time periods: results of the Northwest Regional Screening Program.

To determine the benefit of collecting two routine specimens to test for congenital hypothyroidism, we examined the results of our newborn screening program during the last 9.5 years. The Northwest Regional Screening Program (NWRSP) performs a primary thyroxine test with thyroid-stimulating hormone determinations on the lowest 10% of dried blood filter paper specimens. An initial specimen is obtained in the newborn period, and a routine second specimen is collected at approximately 4 to 6 weeks of age in all infants born in Oregon and 25% of infants born in Idaho, Montana, Alaska, and Nevada. Between May 1975 and October 1984, 182 infants with primary hypothyroidism were detected from 811,917 infants screened, a prevalence rate of 1:4,461. The routine second specimen led to the diagnosis of 19 infants of 484,604 infants screened, a detection rate of 1:25,505. When infants detected by the second screen were compared with those detected by the first screen, they had higher thyroxine and lower thyroid-stimulating hormone concentrations on filter paper and serum specimens. When thyroid scanning was used, all but one infant detected by the second screen had some residual thyroid tissue, whereas 35% of infants detected by the first screen had thyroid aplasia. Skeletal maturation was more likely to be normal in infants detected by the second screen. These infants appear to have milder hypothyroidism due to a later age of onset or slower evolution of thyroid failure. At a cost of $31,881 per infant detected by the second screen, the NWRSP found it cost-effective to obtain a routine second specimen.