Urine collections
All participants were asked to give a urine sample when they
visited the centers between 08.00 a.m. and 5.30 p.m. These spot
urine samples were analyzed for iodine and creatinine. Iodine
excretion was expressed in two ways: as a concentration and as an
estimated 24-h urinary iodine excretion. To calculate the estimated
24-h urinary iodine excretion, the iodine/creatinine ratio was
multiplied by the calculated 24-h creatinine excretion. The calculation of the 24-h creatinine excretion was done by using the
formula:7.54age (years)þ14.15weight (kg)þ3.48height
(cm)þ423.15 for men and6.13age (years)þ9.97weight
(kg)þ2.45height (cm)þ342.73 for women. This formula was
developed for a Danish population.
9
Iodine concentration in urine
was available for 4616 participants in C1a and 2453 in C1b.
Iodine in urine was measured using the CeeAs method after
alkaline ashing as described previously.
10
The recovery of
127
I
(corresponding to 32 mg/L) when added tofifteen urine samples
with a median iodine concentration of 35 (range 15e80)mg/L was
95.9 (SEM 2.4) %. Final values were not corrected for percentage
recovery. Serial dilutions offifteen urine samples containing 15e
80mg I/L gave curves parallel to the standard curve. When a urine
sample measured to contain 93.9mg/L was measured in triplicate in
eighteen assays, the intra- and inter-assay CV for single determinations was 2.1 and 2.7%, respectively. The lowest standard
above the zero blank contained 10mg I/L. The analytical sensitivity
of the set-up varied between 2 and 3mg/L. The standard was