Endocrine Abstracts

Iodine deficiency may lead to reduced thyroid hormone production and ultimately hypothyroidism. The UK has previously been considered to be iodine sufficient, however recent evidence suggests the UK may be iodine deficient. Iodine status can be assessed in several ways, including measurement of urinary iodine excretion, for which inductively coupled plasma-mass spectrometry (ICP-MS) is considered the gold standard method.

An ICP-MS method for determination of urine iodine was developed using an Agilent 7700× instrument with auto-sampler and integrated sample introduction system. Published methods showed discrepancies in the choice of diluent therefore this was optimised. The final diluent was alkali based (tetramethylammonium hydroxide) including tellurium 125 as internal standard. Following method validation, iodine concentration was measured in spot urine samples from 203 individuals (18–70 years) enrolled in a local study recruiting patients with subclinical hypothyroidism (TSH >5 mU/l). These individuals had known thyroid function tests results at the time of urine collection.

Method validation studies demonstrated that the assay allowed accurate, precise, and sensitive quantification of iodine. Intra- and inter-assay coefficients of variation were 3.6 and 3.0% respectively. The limit of detection was 2 μg/l and the limit of quantitation was 1 μg/l. Minimal carryover was observed, and linearity of dilution was demonstrated. Measurement of urine iodine in 203 individuals revealed a median concentration 93 μg/l (range 8–3340 μg/l), consistent with mild iodine deficiency according to World Health Organisation classification. No correlation was found between urine iodine concentration and TSH or free T₄ in this cohort.

An ICP-MS assay for analysis of urine iodine has been successfully developed and validated. Use of this assay demonstrated the presence of mild iodine deficiency in a local cohort, consistent with a previous report suggesting iodine deficiency in the UK. This assay may have utility for further investigating iodine deficiency in the local population.