POPULATION-BASED DIFFERENCES IN THYROTROPIN AND THYROXINE DISTRIBUTIONS IN HEALTHY NEWBORNS - REVEALING RESULTS FROM INDEPENDENT REAGENT EVALUATION

An independent evaluation of reagents for the determination of thyroxi ne and thyrotropin from dried blood spot samples taken from newborns b etween the third and fifth day of life revealed striking differences i n the thyrotropin distribution among newborns from Byelorussia. An ana lysis of the thyrotropin distribution from Byelorussian newborns showe d that 40% of samples had over 5 mIU/l blood. In other European popula tions comparable in respect to timing of blood collection, this fracti on varied from only 1% (Stockholm, Sweden) to 3.7% (Lille, France). Th e reason for the ''shift right'' in Byelorussian newborns remains to b e further investigated. This shift can be attributed to the synergetic effects of mild-moderate iodine deficiency and/or as yet unidentified environmental factors. The differences observed in cumulative distrib ution patterns obtained by two commercial methods question the use of absolute figures (such as the proportion of samples over 5 mIU/l) for the purpose of inter-population comparisons.