SCREENING FOR NEONATAL HYPOTHYROIDISM BY THYROXINE AND THYROTROPHIN RADIOIMMUNOASSAYS USING DRIED BLOOD SAMPLES ON FILTER PAPER

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Abstract
A routine and automatized methodology for thyroxine (T4) and thyrotropin (TSH) radioimmunoassay (RIA) using dried [human] blood samples on filter paper is described. T4-RIA was performed on 1 single dot (5 mm diameter equivalent to 4 .mu.l of serum) while 2 dots were necessary for TSH-RIA. Reference filter papers were introduced in each assay for quality control. In a preliminary study on 4155 neonates, samples generally obtained between the 5-7th day gave a mean dot -T4 of 97.95 .+-. 36.04 nM and a mean dot-TSH of 10.19 mU[units]/l .+-. 8.25, corresponding to 2.47 mU/l of serum. Within an 18 mo. period (Nov. 1976-April 1978), a total of 16,522 neonates were screened allowing detection of 3 cases of congenital hypothyroidism (incidence 1:5507), 2 cases of congenitally low TBG [thyroxine binding globulin] and 33 cases of transient hypothyroidism.