The Amount and form of Radioactivity in Human Milk After Lung Scanning, Renography and Placental Localization 131 I Labelled Tracers

The secretion of radioisotope into mothers' milk was studied after the administration of carriers labelled with 131 I. The radiopharmaceuticals used were 300 μCi macroaggregated human scrum albumin, in short MAA (for lung scanning), 25 μCi ortho‐iodohippuric acid, in short OIH (for renography) and 10 μCi human serum albumin, in short HSA (for placental localization). In the MAA series (7 patients) the maximum radioactivity secreted into milk in the 24 hours following injection was 0.7%, and the mean activity 0.14% of the injected dose. The corresponding figures of the OIH series (25 patients) were 2.4 and 0.32%. In both cases activity was at its maximum during the first 24 hours after injection. In the HSA series (8 patients) the maximum radioactivity secreted into the milk during 24 hours after injection was 0.22% of the injected dose. After the administration of OIH and apparently also of MAA, the radioactivity secreted in 24 hours increases if the excreted volume of milk increases. The radio‐iodine secreted in the milk was not bound to the radiopharmaceutical originally administered, but was mainly in the form of free isotope. The breast feeding of babies whose mothers had undergone lung scanning, renography or placental localization was discussed. It was proposed that milk should be discarded for a minimum of 7 days following lung scanning and a minimum of 2 days following renography, provided the examinations were carried out by means of the radiopharmaceuticals and doses used by the present authors.