[Mail handling: a possible cause of error in the non-selective screening for congenital hypothyroidism]. / Envío por correo: una posible causa de error en el "screening" no selectivo del hipotiroidismo congénito.

Remittance by mail of blood samples and subsequent time of permanency in mail boxes are not supposed to be best thermic conditions for dried blood samples in paper used for neonatal screening. With the idea of checking if temperatures variations can altered or not the content of TSH and T4, some samples of known concentrations of TSH and T4 has been heated to different temperatures between less than -40 degrees C and 100 degrees C during weekly periods. At such temperatures between less than -40 degrees C and 25 degrees C significant hormones losses are not observed. Nevertheless under higher temperatures the percentages of losses increases. Specifically between 37 degrees C and 60 degrees C an hormonal loss of approximately 36% is observed. T4 had also suffered losses of concentration in relation with temperature. These variations make indispensable the change of the way of managing samples that could had suffered modifications with temperatures, and that have been sent by mail. Therefore, considering that about a 40% loss can exist, limit of 40 mu UI/ml should be modified about 25 mu UI/ml.