ALPHA-FETOPROTEIN (α-FP) MEASUREMENT IN DRIED BLOOD SPOTS: A DISCRIMINATING FACTOR BETWEEN TRANSIENT HYPERTHYROTROPINAEMIA AND CONGENITAL HYPOTHYROIDISM

Abstract

α-FP was measured in dried blood spots obtained between the 3rd and 7th day of life by heel-prick from newborns within the operation of the Greek screening programme for congenital hypothyroidism (CH) in newborns, in order to check, if this analyte could serve as a second biochemical index in addition to thyrotropin (TSH) measurement for discriminating newborns with CH from those with transient hyperthyrotropinaemia (TH). α-FP was measured by a RIA method. We studied 60 newborns with CH and 184 newborns with TH. The mean gestational age (GA) of CH group was 39,9±1,5 weeks (mean±SD) and of TH group 39,2±1,9 weeks. Discriminant analysis was used after logarithmic transformation of α-FP values, in order to find the linear combination of α-FPand GA, which best discriminates between CH and TH cases. The mean±SD of α-FP in CH group was 32,6±31,1μg/ml, whereas the corresponding figure for TH group was 13,8±16,0μg/ml, difference statistically significant (p<0,001). The discriminant function of log α-FP and GA was 35,57(log α-FP)+4,89(GA)-341,91. This equation classifies a case to the CH group if it has a positive value and to the TH group otherwise. The misclassification rate is about 26%. In conclusion α-FP values in dried blood spots are significantly higher in CH newborns than in TH ones and the measurement of α-FP in CH screening programmes could offer a diagnostic aid in differentiating CH from TH newborns, especially those with border line TSH values.