Explanation

Iodine: what is measured?

Iodine is a trace element that the thyroid needs to make thyroid hormone. It mainly comes from bread made with iodized baker's salt, iodized table salt, dairy, eggs and sea fish. The thyroid normally has a large store of iodine, and what the body does not need leaves the body in the urine. This analysis measures iodine in the blood; that value mainly follows what you took in during the days before.

What can it detect?

A sign of a very low or, on the contrary, very high recent iodine intake, for example from seaweed, kelp tablets, supplements or a contrast agent containing iodine

Result

What does the result mean?

Iodine too high

A raised iodine is usually due to a recent high intake: kelp or seaweed tablets, a lot of seaweed, supplements with iodine, or a scan with a contrast agent containing iodine. The heart medicine amiodarone also contains a lot of iodine. In most people too much iodine causes no problems, but according to the Netherlands Nutrition Centre (Voedingscentrum) it can disturb thyroid function in people with a thyroid disorder. Symptoms that can then develop are palpitations, nervousness, diarrhea and weight loss despite a good appetite.

Iodine too low

A low iodine may fit a low intake, for example if you eat little or no bread, eat bread without iodized baker's salt (such as much organic or homemade bread) or eat little dairy, eggs and fish. Because the thyroid has a store, according to the Netherlands Nutrition Centre (Voedingscentrum) you often only notice a deficiency after several years. With a long-term deficiency, the thyroid can become underactive and swell (goiter), with symptoms such as weight gain, feeling cold, slowness and constipation. One low blood value does not prove a deficiency, because the value moves with what you ate in the last few days.

After an abnormal result

With an abnormal iodine, the GP usually measures TSH and, if needed, free T4 to see whether the thyroid works properly, and asks about seaweed, supplements, medicines and recent scans with a contrast agent.

Reliability

How reliable is the test?

Iodine in blood mainly follows the intake of the last few days. According to the RIVM (Dutch National Institute for Public Health and the Environment), urine collected over 24 hours is the most accurate way to determine iodine intake. According to the Dutch GP guideline (NHG) on thyroid disorders, whether the thyroid works properly is determined with TSH and, if needed, free T4, not with an iodine measurement. The result of this analysis is therefore hard to interpret.

What can affect the result?

Seaweed, kelp tablets, supplements and products containing iodine in the days before the sample collection raise the value.
A scan with a contrast agent containing iodine or the use of amiodarone can keep the value raised for a long time.
Few laboratories perform the test and reference values are not aligned nationally.

Who it is for

Who is the test useful for?

Useful for

The result says the most as a sign of a very low or very high recent intake, for example from seaweed or supplements. With symptoms that fit an underactive or overactive thyroid, TSH and free T4 are the first tests according to the Dutch GP guideline (NHG). If you eat little bread with iodized baker's salt, dairy, eggs or fish, according to the Netherlands Nutrition Centre (Voedingscentrum) you may have a lower iodine intake; a blood measurement cannot reliably show a deficiency, not even in pregnant women.

How common is it?

In the Netherlands, the soil and food naturally contain little iodine; that is why iodine is added to baker's salt and table salt. According to RIVM research in the north of the Netherlands (2020-2021), men got more than enough iodine and women just enough; in 4 to 7 in 100 women the average intake was below 100 micrograms per day. Intake has fallen by about a third since 2006-2007.

RIVM (report 2022-0066)

Drawbacks and risks

A low result can lead to taking iodine or kelp tablets on your own; the Netherlands Nutrition Centre (Voedingscentrum) advises against kelp tablets because the amount of iodine varies a lot, and too much iodine can disturb the thyroid.
Because the value moves with the diet of the last few days, a single measurement can cause unnecessary worry.

Get tested

Iodine: test panels

Iodine is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.

Blood draw
Iodine
Iodine; thyroid hormone synthesis.
€ 51,00

Evidence

Sources

This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.

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