Newborn screening limitations

Limitations of newborn screening include timeliness of screening and diagnosis, false negatives, and disorders not included on the newborn screening panel. 

Some labs utilize second-tier testing to limit false positives while avoiding false negatives. Second-tier analysis is based on more conservative cutoffs, in order for more newborn screens to initially flag as abnormal. Abnormal newborn screens in tier one will undergo more specialized studies immediately from the same newborn screening card. Only those samples that have abnormal second-tier studies will be reported as abnormal. This limits the number of infants... 

The disappearance of xanthurenic acid after pyridoxine dierapy suggested the possibility of a latent Be deficiency (Dl). Dahler-Vollen-weider (D2) screened 159 children in respect to the urinary picture of tryptophan metabolites and found an abnormal excretion of xanthurenic acid in 17, whereas 142 fell within normal limits after tryptophan loading. There seems to be an increased rate of excretion widi age. In the newborn the excretion was the lowest while the maximal values were found in the age group 10-16 years. During periods of rapid growth there was a high excretion rate of xanthurenic acid, which was not appreciably affected by daily oral administration of 100 mg pyridoxine. 

Virtually 1(X) % of Swiss newborns are screened for congenital hypothyroidism. In the Central Laboratory of the Swiss Red Cross in B e, which screens about one third of the babies bom in Switzerland, the recall rate for TSH values over 20 mU/1 was O.S to 0.6 per KXX) in 198S and 1986. After lowering the recall limit to 15 mU/1 the recall rate was 2.2 per KXX) in 1987. 

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