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      Rate of Recalls in Congenital Hypothyroidism Based upon a Regional Survey in Isfahan, Iran, Using Serum T4 and TSH Analyses: Comparison of Two Different Recall Methods

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          Aims: To evaluate and compare the recall rate in congenital hypothyroidism screening project in Isfahan, first using an approach involving measures of both TSH and T4 and then using TSH alone. Methods: From June 2002 to January 2005, serum TSH and T4 level of referred neonates were measured at 3rd to 7th day of birth through venous sampling. If neonates’ serum TSH was >20 mIU/l or T4 was <6.5 µg/dl by the first protocol, or TSH was >20 mIU/l by the second protocol, they were recalled. TSH and T4 were measured using an immunoradiometric assay and radioimmunoassay, respectively. Neonates with TSH > 10 and T4 < 6.5 on their second measurement were considered as congenitally hypothyroid. Results: Serum T4 and TSH of 29,425 neonates by first and 57,235 neonates by second recall approach were measured. Recall rate was higher in the first protocol (2.2% vs. 0.6%, p < 0.05). Most of the recalled neonates in the first protocol were recalled for low T4 level (p < 0.05). The prevalence of CH was 1 in 350 livebirths. Conclusion: Although the recall rate was in the acceptable range by either approach, the TSH alone protocol seems to be a more sensitive and practical approach with the least recall burden and considering the high prevalence of CH in our region merit adaptation of widespread screening for CH using TSH measurements from heel stab blood spotted on filter paper.

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          Most cited references 5

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          Increased recall rate at screening for congenital hypothyroidism in breast fed infants born to iodine overloaded mothers.

          Skin disinfection with povidine-iodine (PVP-I) is widely used in obstetrics. We evaluated the influence of PVP-I in mothers at delivery on the serum thyroid stimulating hormone concentrations of their infants at the time of screening for congenital hypothyroidism. The study covered 4745 infants who were either breast fed (3659, 77%) or bottle fed (1086, 23%); 3086 (65%) of them were born to mothers with no iodine overload (controls) and 1659 (35%) to mothers with iodine overload. Compared with the control group, the breast and bottle fed infants born to mothers with iodide overload had a shift of neonatal thyroid stimulating hormone concentration towards high values. The shift was maximal in the breast fed infants with a 25 to 30 fold increase in the recall rate at screening for congenital hypothyroidism (serum thyroid stimulating hormone greater than 50 mU/l) while in the bottle fed infants, the recall rate was barely modified. In conclusion, the use of PVP-I in mothers at delivery induces a transient impairment of thyroid function in their infants, especially if breast fed. This situation is detrimental to screening for congenital hypothyroidism. Consequently PVP-I is not recommended in obstetrics.
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            Thyroid function in very low birth weight infants: effects on neonatal hypothyroidism screening.

            To supply normative data for screening thyroxine (T4) and thyrotropin concentrations correlated with birth weight and age at screening of infants with birth weights ranging from 400 to 5500 gm, and to document the effects of screening of very low birth weight (VLBW) infants, because VLBW infants comprise 0.86% of surviving newborn infants and have very low total T4 concentrations with normal or elevated free T4 concentrations as a result of deficient protein binding of thyroid hormones. Both retrospective and prospective studies were used. We conducted retrospective analyses of screening of T4 and thyrotropin concentrations in 9,324 term, 18,946 low birth weight, and 3,450 VLBW infants in Massachusetts, and a prospective study of T4 and thyrotropin concentrations in 48 VLBW infants at 2 weeks of age. Forty of the infants also had hormone measurements at 4 weeks, 29 at 8 weeks of age, and 24 had analysis of cord blood samples. Median T4 concentrations for each weight group (in 250 gm increments) increased progressively and significantly up to 2500 gm. Of the surviving VLBW infants, 1.5% had screening T4 concentrations that were unmeasurably low ( or = 40 mU/L correlates inversely with weight. The incidence of early, transient hypothyroidism in VLBW infants defined by this thyrotropin concentration was eight times that in term infants. Two infants had late-onset, transient hypothyroidism at 2 and 7 weeks, respectively. The normative data related to birth weight and age at screening allow proper interpretation of VLBW results for primary T4 and primary thyrotropin screening programs. Screening of the concentrations of T4 and thyrotropin in VLBW increases the number of secondary measurements of T4 in a primary thyrotropin screening program and the number of secondary thyrotropin measurements in a primary T4 screening program by 6% and 9%, respectively. We recommend screening analyses for VLBW infants in the latter part of the first week of life and again at 2 and 4 to 6 weeks of age. This protocol would increase the number of screening analyses by 1.6%.
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              Evaluation of three thyroid-function screening tests for detecting neonatal hypothyroidism.

               P Walfish (1976)
              Three thyroid-function detection methods were evaluated concomitantly for possible application as routine screening tests for the early diagnosis of neonatal hypothyroidism. Dried capillary-blood thyroxine (T4) was measured on eluted filter-paper discs for 9734 3-5-day old neonates. Serum T4 and thyroid-stimulating hormone (T.S.H.) assays from cord blood were studied as alternative screening tests on 4911 and 3733 infants, respectively. To avoid false-negative results, neonatal blood-T4 and cord serum-T4 screening methods were followed up for the lower 10th and 6th percentile, respectively. This resulted in a false-positive recall incidence greater than 92% owing to various additional factors which also influence T4 levels: thyroxine-binding-globulin deficiency, prematurity, and maternal drug ingestion. In marked contrast, cord T.S.H. as an initial screening test had a higher specificity and sensitivity for the diagnosis of primary hypothyroidism with the two affected cases, having values greater than 70 muU/ml (with only 0-24% of the screened population having values greater than 50 muU/ml). In order to avoid the impracticably high recallrate and false-positive incidence resulting from an initial T4 screening test, and to reduce the estimated follow-up recall to less than 0-2% of the screened infant population, it is recommended that infants with low T4 be selected for a supplementary T.S.H. screening test.

                Author and article information

                Horm Res Paediatr
                Hormone Research in Paediatrics
                S. Karger AG
                December 2005
                05 December 2005
                : 64
                : 6
                : 287-292
                aIsfahan Endocrine and Metabolism Research Center, bDepartment of Pediatrics, Medical School, Isfahan University of Medical Sciences and Health Services, Isfahan, Iran
                89488 Horm Res 2005;64:287–292
                © 2005 S. Karger AG, Basel

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                Page count
                Figures: 3, Tables: 2, References: 24, Pages: 6
                Original Paper


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