Measurement of thyroid-stimulating hormone in dried blood spot

Blood T.S.H. (thyroid-stimulating hormone) was measured by radioimmunoassay in dried blood spotted onto filter-paper and obtained during screening of the newborn for metabolic disorders. By this method, the detection limit for blood T.S.H. was 5--10 muU/ml, which is the approximate upper limit of normal for blood T.S.H. T.S.H. values obtained on dried blood correlated well with those obtained on serum from the same subjects. Duplication of the assay in a single sample is not necessary. This method picked up a case of primary hypothyroidism in a four-year-old girl with symptoms. Since the technique is simple and sensitive enough for the detection of hypothyroidism, it could be valuable in mass-screening for congenital hypothyroidism.