[Radioimmunologic determination of TSH in dried blood stains: a possible screening method for the diagnosis of hypothyroidism in new born infants].

Abstract

By a modification of the radioimmunoassay of TSH in plasma, a method has been introduced for the measurement of TSH in dried blood spotted on filter paper. On incubation of filter paper discs (6.5 mm diameter, corresponding to approx. 10 mul blood) for 38 hs has the lower limit of detection was 10 muU/ml TSH 68/38. In 100 blood samples, TSH was measured in plasma as well as in dried blood; the results were comparable and showed complete agreement in patients with high TSH concentrations suffering from primary hypothyroidism. In 16 out of 72 newborn children examined during the first 8 hs of life. TSH was slightly elevated. It would appear that our method is sensitive enough for detection of the physiological postnatal rise in TSH. Among 1400 infants in whom Tsh was measured on the 5th or 6th day simultaneously with routine screening for phenylketonuria (PKU), we found 1 case with markedly elevated TSH levels of greater than 100 muU/ml. The child suffered from congenital goiter. The results of our study show that the measurement of TSH in dried blood spots is possible without particular difficulty. Becasue of the simplicity of blood-sampling, the stability of the TSH, the relatively low cost and the low number of false positive results, this method seems to be suitable for screening of new born infants. It could be carried out conveniently in combination with the screening program for metabolic diseases, which covers practically 100% of infants born in Switzerland. Congenital hypothyroidism is a relatively frequent disease (1:3000-1:7000) in which early commencement of treatment is of great importance for mental development. It would therefore be desirable for all infants to be screened during the first days of life for congenital hypothyroidism.