Measurements of TSH, T4 and Phe in samples of umbilical cord blood on filter paper: impact on neonatal screening

Abstract

There is a consensus on considering congenital hypothyroidism and phenylketonuria as theoretical and practical models in neonatal screening. The tendency toward early discharge in sorne rnaternity hospitals dueto socioeconomic reasons led us to implement screening prograrns in umbilical cord blood samples. Titres of total T4, TSH and Phe in cord blood on S&S 2992 filter paper from 458 neonates were performed using fluorescent ultrarnicroassays. Frequency distribution for TSH concentrations showed a mean of 1.7 mUl/l; 98% of the samples had concentrations within the 0-10 mUl/l range, 1.7 % within 10-20 mUl/l and one sarnple with a value higherthan 20 mUl/l. The rnean value was 177.2 nmol/l for T4, 90.2% within 116-370 nmol/l, 9.6 % within 60-116 nmol/l and one sample with a value lower than 60 nmol/l. For Phe, the mean concentration was 41 6 µmol/l (0.7 mg/dl), 80.3 % within the range 0-60 µmol/l (0-1 mg/dl), 19.2 % within 60-120 µmol/l (1-2 mg/dl) and two samples with a value higher than 120 µmol/l (2 mg/dl). Results showed that the use of cord blood samples in early diagnosis of congenital hypothyroidism is convenient. However, cord blood Phe levels were lower. Thus, they do not guarantee total effectiveness in the detection of phenylketonuria.