Topical iodine and neonatal hypothyroidism
C. M. Gordon, D. H. Rowitch, M. L. Mitchell and I. S. Kohane
Division of Endocrinology, Children's Hospital, Harvard Medical School, Boston, Mass, USA.
OBJECTIVES: To determine whether skin care practices with iodine-containing
disinfectants are putting patients in the neonatal intensive care unit at
risk for primary hypothyroidism. Cutaneous exposure to povidone-iodine
antiseptic solutions may be a cause of primary hypothyroidism in neonates.
DESIGN: Prospective pilot study. SETTING: Level III neonatal intensive care
unit of a university-affiliated hospital. PARTICIPANTS: Sequential sample
of 47 medial and surgical patients admitted to the neonatal intensive care
unit who received cutaneous povidone-iodine applications in preparation for
invasive or surgical procedures. METHODS: Seven to 10 days after iodine
exposure, capillary blood samples were obtained on filter paper blots for
thyroid function testing and urine samples were collected to determine
quantitative iodine concentrations. A plasma creatinine level was
determined for each subject. RESULTS: A total of 47 patients were enrolled.
The gestational ages of subjects ranged from 26 to 41 weeks (mean, 33.6
weeks); the male-to-female ratio was 28:19; and the birth weights ranged
from 0.7 to 5.1 kg(mean, 2.42 kg). The thyroxine level ranged from 20 to
187 nmol/L (1.6 to 14.6 micrograms/dL) (mean, 102 nmol/L [7.9
micrograms/dL];reference, > or = 90 nmol/L [> or = 7 micrograms/dL];
and the thyrotropin level ranged from 0.1 to 16.5 mU/L (mean, 6.4 mU/L;
reference, < 20 mU/L). The mean uridine iodine concentration was 2798.0
micrograms/dL (reference, < 40 micrograms/dL), and the mean plasma
creatinine level was 60 mumol/L (0.69 mg/dL) (reference, < or = 50
mumol/L [ < or = 0.6 mg/dL] for males and < or = 40 mumol/L [ < or
= 0.5 mg/dL] for females). CONCLUSIONS: There was no documentation of
primary hypothyroidism in our subjects despite elevated urine iodine
levels. While it is still possible that patients who receive long-term
iodine exposure in other settings (eg, cardiac catheterization) are at risk
for primary hypothyroidism, our study suggests that the amount of iodine
absorbed through routine neonatal intensive care unit procedures does not
substantially alter thyroid function during the first 10 days of life. An
important confounding variable is that seven patients were receiving
dopamine hydrochloride infusions and four were receiving dexamethasone
phosphate at the time of sample collection. We therefore cannot rule out
the possibility that these medications masked a thyrotropin level elevation
that would have occurred in a primary hypothyroid state. We discuss
implications for the interpretation of the results of neonatal thyroid
function tests.
