Atypical Hypothyroidism and the Very Low Birthweight Infant

Abstract

Results of thyroid screening tests were examined retrospectively on 311,282 infants born in Massachusetts from January 1, 1993 to December 31, 1996. During this period, 118 infants were found to have typical hypothyroidism, characterized by a low thyroxine (T4) and an elevated thyrotropin (TSH) on the initial newborn-screening specimen. Of these, 98 were normal birthweight (NBW, > or = 2,500 g), 9 were low birthweight (LBW, 1,501-2,499 g), and 11 were very low birthweight (VLBW, < or = 1,500 g). Atypical hypothyroidism as defined here is characterized by a low T4 and normal TSH concentration on the initial screening specimen, followed by and elevated TSH level on a repeat blood specimen. This phenomenon occurred in 18 infants, of whom 4 were NBW, 4 were LBW, and 10 were VLBW. The incidence of combined typical and atypical hypothyroidism was: NBW, 1:3051; LBW, 1:1589; VLBW, 1:153, with the highest incidence of atypical hypothyroidism in the VLBW category (48% of cases in this weight category, 56% of all cases of atypical hypothyroidism). In addition, screening programs using a primary TSH screen will miss infants with atypical hypothyroidism. In view of these results, it is suggested that T4 measurements be obtained routinely in all LBW and VLBW infants, with additional routine repeat blood specimens.

Screening for congenital hypothyroidism: the value of retesting after four weeks in neonates with low and very low birth weight

“…6,11 In our study, a repeat TSH test detected 19 low or very low birth weight infants with TSH levels >10mIU/L, among whom permanent or transient hypothyroidism was subsequently detected in five. Similar results were obtained by Mandel et al 12 Our observations are also in agreement with data reported by Fisher et al, 6 which showed a prevalence of primary thyroid dysfunction of about 0.5%.…”

Overall usefulness of newborn screening for congenital hypothyroidism by using free thyroxine measurement

“…NICU, and newborns from multiple births [4,[12][13][14][15][16]. In these situations, the diagnosis of CH-T may be overlooked due to the suppression of the TSH level as a result of various drugs, hypothalamo-pituitary immaturity, and other effects of serious illness [17,18].…”

“…Although hypothyroidism under these conditions may be self-limiting, it can lead to intellectual disabilities if it is not detected and treated [11]. In addition, FT4 measurement may enable the identification of newborns with CH-T with delayed TSH elevation-found mainly in premature and/or low birth weight (LBW) newborns-who may not be identified by a primary TSH strategy [2,4,[12][13][14].…”

Wrodzona niedoczynność tarczycy — polskie rekomendacje dotyczące leczenia, monitorowania terapii i badania przesiewowego w specjalnych kategoriach noworodków z wysokim ryzykiem niedoczynności tarczycy

“…In the study groups with a positive effect of L-thyroxine on the development of preterm babies, a dose of 6-8 μg/kg body weight was used, slightly improving mental development after 5-10 years. However, the greatest problem with decision making is a lack of universal reference values for fT4 and fT3 in preterm newborns [42][43][44][45][46][47][48][49][50][51]. Venous blood TSH values in preterm babies in the first week of life determined with a TSH third-generation test oscillating between 0.7 mIU/l and 27.0 mIU/l [52].…”

“…W dotychczas obserwowanych grupach, w których stwierdzono pozytywny wpływ leczenia L-tyroksyną na rozwój wcześniaków, stosowano dawkę 6-8 μg/kg masy ciała, co powodowało nieco lepszy rozwój umysłowy widoczny po 5-10 latach. Jednak największym problemem przy podejmowaniu decyzji jest brak jednolicie opracowanych wartości referencyjnych fT4 i fT3 u noworodków przedwcześnie urodzonych [42][43][44][45][46][47][48][49][50][51]. Wartości TSH w surowicy krwi żylnej u wcześniaków w pierwszym tygodniu życia oznaczane testem trzeciej generacji oscylują pomiędzy 0,7 mIU/l a 27,0 mIU/l [52].…”