NEONATAL SCREENING FOR CONGENITAL HYPOTHYROIDISM USING THE FILTER-PAPER THYROXINE TECHNIQUE

A total of 25,244 full term consecutive newborns were screened for hyp othyroidism at 24 to 96 h of birth using the filter paper technique fo r thyroxine. The screening protocol based on our pilot study considere d filter paper thyroxine (FP-T4) values of 51 to 80 ng/ml (-1 SD) as b orderline and < 50 ng/ml (-2 SD) as high risk for congenital hypothyro idism. FP-T4 and /or serum T4 and TSH were reestimated in all neonates with FP-T4 < 80 ng/ml. A total of 4775 (18.9%) newborns (FP-T4, 51 to 80 ng/ml in 4435 and < 50 ng/ml in 340) needed the recall; 2237 (50.4 %) with FP-T4 51 to 80 ng/ml recalled by letters and 283 (83.3%) of th e 340 subjects with FP-T4 < 50 ng/ml recalled by home visit, responded by 6 wk of age. Congenital hypothyroidism was confirmed in 6 newborns . FP-T4 in one persisted at 55 ng/ml on follow up and in the remainder both initial and repeat values were < 50 ng/ml. Follow up serum T4 va lues were subnormal (7.8 - 50.2 ng/ml) and serum TSH elevated (80 - 12 33 IU/ml). Technetium thyroid scan showed agenesis in 3, ectopia in 2 and normal gland with probable dyshormonogenesis in one. Three other n ewborns (FP-T4 93 to 143 ng/ml) escaped primary detection and were ref erred later for congenital hypothyroidism. The incidence of congenital hypothyroidism by nprimary screening was 1:4207 (6 of 25,244) but wit h these 3 missed cases, probably 1:2804. Congenital hypothyroidism was reconfirmed in all 9 infants between the ages of 2 1/2 to 4 yr. TBG d eficiency was detected in 3 male infants (1:8415). A cut off at 65 ng/ ml (-1.5 SD) would have reduced the recall rate to 6.75 per cent and y et detected all 6 infants with congenital hypothyroidism. Based on pas t experience we would advocate primary TSH screening which is more dis criminatory and has a lower recall rate.