Trace Element: Iodine (I) (SAAS)
Biochemistry Overview / Directory
Purpose of the test
Iodine is an essential trace element required for the synthesis of thyroid hormones, thyroxine and triiodothyronine, which in turn control various metabolic processes and are thus essential for growth and development. Iodine is rapidly absorbed from dietary sources (as iodide) via the GI Tract and is largely confined to the extra-cellular fluid with some found in red blood cells. Iodine concentrates primarily in the thyroid, saliva and mammary glands and stomach via a sodium-iodide symporter.
Iodine deficiency is a global problem, especially in areas where the iodine content in the soil is low. Deficiency is rare in developed countries but may still arise if subjects are persistently consuming low-iodine containing diets. Severe deficiency during pregnancy may result in still births, perinatal death or low-birth weight babies. Surviving offspring may present with neurological defects- due to irreversible damage to the brain and CNS. Severe iodine deficiency in infancy leads to poor growth and developmental delay.
The recommended daily dosage for iodine (NRC of US National Academy of Sciences), depending on age is 40-150µg, with fish and sea-weed being a rich source. Intake needs to be increased during pregnancy. There is a high tolerance to ingested iodine: A dietary limit of 2mg/d is thus indicated, though intakes of up to 5mg/d or higher have been reported to have no ill effects.
Accidental/suicidal ingestion can cause corrosive damage to the GI tract. Commoner causes of iodine toxicity include the heavy application of iodine (as povidone-iodine) to open wounds, large injections of iodine radio-contrast media, amiodarone treatment and large intake of dairy products or kelp (eaten in large amounts in Japan).
As iodine is primarily cleared via the kidneys, measurement in the urine is the most practical indicator for ascertaining iodine intake/status. A 24h collection is advisable though random samples are usable. Additional information can be provided by thyroid function tests. Hair is not a useful for indicating iodine exposure, as the iodide which layers on the external surface of the hair root can be easily removed during washing.
Sample Requirements
A 24h collection in an acid washed container is preferred but a random sample (NOT the first (overnight) sample) provided in a sterile plastic universal is usable. If a 24h collection is available, please provide an aliquot of the collection in a plastic universal (but note the total volume on the sample and/or request form). A volume of 10ml is adequate for analysis.
Storage and Transport
Store sample(s) in the fridge (short term). For longer periods store samples at -20oC.
Transport the sample(s) in appropriate package via first class mail.
Turnaround Time
10 working days.
Price
Price available on application - please contact adrianturner1@nhs.net. Discounts could be available for significant workloads.
Contacts
Dr Kishor Raja
T: 020 3299 4127
