An iodine blood test measures iodine in serum or plasma, the liquid part of blood. Iodine is a trace mineral your thyroid uses to make thyroxine (T4) and triiodothyronine (T3), the hormones that help regulate metabolism, growth, temperature control, pregnancy development, and many body systems. A blood iodine result can help check for iodine overload, recent high exposure, or possible low iodine status, but it is not the most common first test for iodine nutrition. Urinary iodine is used more often for population iodine status because most absorbed iodine leaves the body in urine.
Normal blood iodine ranges vary by laboratory and method. A result that looks “normal” on one lab report may be flagged differently by another. The best interpretation combines your blood iodine value with your diet, supplements, medications, recent contrast imaging, kidney function, and thyroid tests such as TSH and free T4.
- A common serum iodine reference range is about 40–92 mcg/L, while another major lab uses 52–109 mcg/L.
- Blood iodine is usually ordered to assess iodine overload, monitor iodine-containing drugs, or clarify unusual thyroid-related findings.
- Low blood iodine can suggest low intake, but a single blood result does not prove iodine deficiency by itself.
- High blood iodine often comes from iodine contrast, amiodarone, kelp, iodine drops, or other high-dose iodine products.
- Iodine results should be interpreted with thyroid markers because both too little and too much iodine can disturb thyroid function.
- Pregnant and breastfeeding people need more iodine and should not start high-dose iodine without clinician guidance.
Table of Contents
- What the Iodine Blood Test Measures
- Iodine Blood Test Normal Range
- How to Read Your Iodine Result
- Low Iodine Blood Test Results
- High Iodine Blood Test Results
- Blood Iodine vs Urine Iodine
- Preparation and Result Factors
- Next Steps After Abnormal Results
What the Iodine Blood Test Measures
The iodine blood test measures iodine concentration in serum or plasma, usually reported in micrograms per liter (mcg/L). Some laboratories report the same concentration as nanograms per milliliter (ng/mL). For iodine, 1 ng/mL equals 1 mcg/L, so a value of 80 ng/mL is the same as 80 mcg/L.
Iodine in the bloodstream reflects the iodine available after recent intake, absorption, redistribution into tissues, and elimination through the kidneys. The thyroid gland takes up iodide from blood and uses it to make thyroid hormones. Most of the body’s iodine is stored in the thyroid, not circulating freely in blood.
A blood iodine test is most useful when a clinician wants to evaluate:
- Possible iodine overload from medication, contrast dye, kelp, or iodine drops
- Unexplained thyroid changes after high iodine exposure
- Iodine status when urine testing is not enough or not practical
- Iodine-containing drug monitoring, especially with amiodarone
- A possible exposure pattern in someone with thyroid symptoms
This test does not directly measure thyroid hormone production. A person can have an iodine result within range and still have hypothyroidism, hyperthyroidism, thyroid autoimmunity, or another thyroid disorder. For that reason, iodine is usually interpreted alongside TSH, free T4, sometimes free T3, thyroid antibodies, and clinical history.
Iodine also belongs in a broader nutrient context. People being assessed for several nutrient problems may have iodine checked as part of a vitamin and mineral blood test panel, especially when diet restriction, malabsorption, pregnancy, or supplement overuse is part of the picture.
Iodine Blood Test Normal Range
A typical serum or plasma iodine reference range is roughly 40–109 mcg/L, depending on the laboratory. Two commonly cited lab ranges differ enough that you should always use the range printed next to your result.
| Specimen | Example reference range | Units | Important note |
|---|---|---|---|
| Serum iodine | 40–92 | mcg/L or ng/mL | Used by some specialty laboratories for serum iodine interpretation. |
| Serum or plasma iodine | 52–109 | mcg/L | Used by another major laboratory for serum/plasma iodine testing. |
| Pregnancy research ranges | Often population-specific | mcg/L | Pregnancy reference intervals are still being studied and should not be applied across all patients. |
Reference ranges differ because laboratories may use different specimen types, collection tubes, instruments, calibration methods, and population data. Many iodine blood tests use inductively coupled plasma mass spectrometry, often shortened to ICP-MS. This method can measure trace elements at very low concentrations, but the sample must be collected and handled carefully to avoid contamination.
There is no single universal “optimal” serum iodine range that applies to every adult, child, pregnant person, thyroid condition, or iodine exposure scenario. A value of 95 mcg/L may be normal at one lab and slightly high at another. A result just outside the listed range may matter less than a clear pattern: recent contrast exposure, kelp supplement use, low iodine diet, abnormal TSH, or symptoms that fit thyroid dysfunction.
For practical use:
- Use your lab’s reference interval first.
- Check whether your result is serum, plasma, whole blood, or urine.
- Check the unit before comparing values.
- Do not compare a blood iodine number directly with urinary iodine cutoffs.
- Interpret borderline results with thyroid markers and exposure history.
How to Read Your Iodine Result
The most useful interpretation starts with three questions: Is the result below range, within range, or above range? Was there a recent iodine exposure? Are thyroid tests normal?
A normal iodine blood result usually means there is no obvious blood evidence of iodine deficiency or overload at the time of testing. It does not prove that iodine intake has been ideal for months, and it does not rule out thyroid disease. Many thyroid conditions are driven by autoimmune disease, nodules, inflammation, pituitary signaling, medication effects, or previous thyroid treatment rather than iodine intake alone.
A low result suggests that circulating iodine is below that laboratory’s expected range. This may fit with low dietary intake, pregnancy-related increased need, breastfeeding, avoidance of iodized salt, limited seafood and dairy intake, or restrictive eating patterns. It may also need confirmation because iodine levels can shift with recent intake and sample timing.
A high result suggests excess circulating iodine or recent exposure. This is especially common after iodinated contrast for CT scans or angiography, iodine-containing medications, kelp tablets, high-dose “thyroid support” supplements, Lugol’s solution, potassium iodide products, or repeated topical iodine use over large skin areas.
| Result pattern | Common meaning | Usual follow-up |
|---|---|---|
| Below range | Possible low iodine intake or increased iodine need | Review diet, pregnancy/lactation status, urinary iodine, TSH, and free T4. |
| Within range | No obvious iodine overload or low circulating iodine | Interpret with symptoms, thyroid tests, and reason for ordering. |
| Mildly above range | Recent iodine exposure or supplement intake | Check contrast imaging, kelp, iodine drops, multivitamins, and medications. |
| Markedly high | Iodine overload is more likely | Assess thyroid function and stop nonessential iodine sources only with clinician guidance. |
The same iodine result can mean different things in different people. A mildly high iodine level after a recent contrast CT may be expected. The same value in someone with unexplained palpitations, weight loss, and low TSH may raise concern for iodine-triggered hyperthyroidism. A borderline low iodine level in a nonpregnant adult with normal TSH and a varied diet may need repeat testing or urine testing before any treatment decision. The same result in early pregnancy deserves closer attention because iodine needs rise during pregnancy.
Low Iodine Blood Test Results
A low iodine blood test means the serum or plasma iodine concentration is below the lab’s reference range. It can suggest inadequate iodine intake, but it should not be treated as a stand-alone diagnosis. Iodine deficiency is usually assessed through a combination of diet history, urinary iodine, thyroid function tests, thyroid size when relevant, pregnancy status, and symptoms.
Common reasons for low iodine include:
- Avoiding iodized salt while also eating little seafood or dairy
- Vegan or dairy-free diets without iodine-fortified foods
- Pregnancy or breastfeeding, when iodine needs are higher
- Low intake during weight-loss dieting or highly restricted diets
- Living in or coming from a region with low iodine soil and limited iodized salt use
- Long-term use of specialty salts that are not iodized, such as many sea salts, kosher salts, and Himalayan salts
- Some malabsorption conditions or gastrointestinal surgery
- Heavy reliance on plant-based milk alternatives that are not iodine-fortified
Low iodine can reduce thyroid hormone production when intake is low enough. The thyroid may respond by increasing iodine uptake and, over time, enlarging into a goiter. In adults, significant deficiency may contribute to fatigue, cold intolerance, constipation, dry skin, slowed heart rate, weight gain, heavy menstrual bleeding, or elevated TSH. These symptoms overlap with many other conditions, so lab confirmation matters.
A low iodine result is especially important during pregnancy and lactation. Thyroid hormone supports fetal and infant brain development, and iodine needs rise because of increased thyroid hormone production, kidney iodine losses, and iodine transfer to the fetus or breast milk. Pregnant people should not self-treat low iodine with high-dose supplements. The safer approach is to review prenatal vitamin iodine content, diet, thyroid tests, and iodine testing with a clinician.
Low iodine often appears with normal TSH at first. TSH is not a sensitive early marker of iodine deficiency in every person. Thyroglobulin, urinary iodine patterns, thyroid size, and dietary assessment may add context. If the result is truly low, a clinician may suggest reasonable dietary correction, such as iodized salt in appropriate amounts, seafood, dairy if tolerated, eggs, or a standard-dose iodine-containing prenatal or multivitamin when appropriate.
For a deeper explanation of low results, causes, and thyroid-related follow-up, see low iodine blood test meaning.
High Iodine Blood Test Results
A high iodine blood test means the serum or plasma iodine concentration is above the lab’s expected range. High iodine is often caused by exposure rather than ordinary food intake. The most common clues are recent imaging contrast, amiodarone, kelp, iodine drops, or high-dose supplements.
Common causes of high iodine include:
- Iodinated contrast used for CT scans, angiography, or other imaging
- Amiodarone, a heart rhythm medication that contains a large amount of iodine
- Kelp, bladderwrack, seaweed capsules, and some “thyroid support” products
- Lugol’s iodine, nascent iodine, potassium iodide, or SSKI
- Repeated use of iodine-containing antiseptics on large wounds or burns
- Very high seaweed intake, especially kelp or kombu
- Occupational or environmental iodine exposure
- Reduced kidney clearance in some people
High iodine does not always mean toxicity, but it can stress the thyroid in susceptible people. Excess iodine can temporarily reduce thyroid hormone production through the Wolff-Chaikoff effect. Most healthy thyroid glands adapt, but some people do not escape this effect well and may develop hypothyroidism. Others, especially people with nodular thyroid disease or previous iodine deficiency, may develop iodine-induced hyperthyroidism.
People at higher risk from excess iodine include those with Hashimoto’s thyroiditis, Graves’ disease, multinodular goiter, thyroid nodules, previous thyroid disease, older adults, newborns, and people taking amiodarone. A high blood iodine result in these groups deserves careful thyroid follow-up even when symptoms are mild.
Symptoms that may suggest iodine-related hyperthyroidism include fast heartbeat, palpitations, tremor, heat intolerance, sweating, anxiety, unexplained weight loss, frequent bowel movements, and trouble sleeping. Symptoms that may suggest iodine-related hypothyroidism include fatigue, cold intolerance, constipation, dry skin, low mood, weight gain, puffy face, hoarse voice, and slow pulse.
Seek urgent medical care for chest pain, fainting, severe shortness of breath, confusion, very fast or irregular heartbeat, high fever with agitation, or severe weakness. These symptoms are not specific to iodine, but they can signal serious thyroid, heart, or metabolic problems.
Do not stop prescribed amiodarone, antithyroid medication, or potassium iodide without medical advice. Instead, list all iodine exposures and ask whether TSH, free T4, free T3, thyroid antibodies, kidney function, and repeat iodine testing are needed. For more detail on excess iodine sources and thyroid risk, see high iodine blood test causes.
Blood Iodine vs Urine Iodine
Blood iodine and urine iodine answer related but different questions. Blood iodine measures iodine circulating in serum or plasma. Urinary iodine measures iodine leaving the body in urine. Since most absorbed iodine is excreted in urine, urinary iodine is widely used to assess recent iodine intake across groups of people.
The biggest limitation is individual interpretation. A single spot urine iodine result can swing widely from day to day depending on meals, hydration, salt use, and supplement timing. For populations, the median value from many people is useful. For one person, repeated spot urine tests or a 24-hour urine collection can give a clearer picture than a single spot sample.
WHO-style urinary iodine cutoffs apply mainly to populations, not to diagnosing one individual from one sample. They are still helpful for understanding iodine status categories.
| Group | Median urinary iodine concentration | Population interpretation |
|---|---|---|
| School-age children and nonpregnant adults | Less than 100 mcg/L | Insufficient iodine intake |
| School-age children and nonpregnant adults | 100–199 mcg/L | Adequate iodine nutrition |
| School-age children and nonpregnant adults | 200–299 mcg/L | Above requirements |
| School-age children and nonpregnant adults | 300 mcg/L or higher | Excessive intake at the population level |
| Pregnant women | 150–249 mcg/L | Adequate iodine nutrition |
| Pregnant women | 500 mcg/L or higher | Excessive intake at the population level |
These urine values should not be compared with serum iodine ranges. A urine iodine of 160 mcg/L and a serum iodine of 80 mcg/L do not mean the same thing. They come from different specimen types, different physiology, and different reference systems.
Blood iodine may be more useful when the question is iodine overload from medication or contrast. Urine iodine may be more useful when the question is recent dietary intake. Thyroid tests show whether iodine status is affecting thyroid function. In some situations, thyroglobulin adds information about longer-term iodine strain on the thyroid, especially in pregnancy or population studies.
Because iodine, selenium, iron, and vitamin D can all affect thyroid-related physiology in different ways, clinicians may also check other nutrient markers when symptoms or diet history point in that direction. Selenium is one example because it supports enzymes involved in thyroid hormone metabolism; abnormal results may lead to follow-up such as a selenium blood test.
Preparation and Result Factors
Most people do not need to fast for an iodine blood test unless the lab or clinician gives specific instructions. The more important preparation step is an accurate exposure history. Iodine can rise sharply after certain medicines, supplements, and procedures, so the timing of the test matters.
Before testing, tell your clinician and the lab about:
- CT scans, angiograms, or other imaging with iodinated contrast in the past several weeks
- Amiodarone or other iodine-containing medicines
- Kelp, seaweed capsules, iodine drops, thyroid support supplements, or potassium iodide
- Prenatal vitamins, multivitamins, and mineral formulas
- Recent radioactive iodine treatment or thyroid cancer preparation diets
- Large wound care, burns, or repeated use of povidone-iodine antiseptics
- Kidney disease or reduced kidney function
- Pregnancy, breastfeeding, or trying to conceive
Do not stop prescribed medication just to “clean up” the result. A high iodine value caused by amiodarone or contrast is still clinically useful because it tells the clinician what your thyroid has been exposed to. Stopping a heart rhythm medication without medical supervision can be dangerous.
Sample handling can also affect accuracy. Trace-element testing usually needs special collection materials, such as a trace metal-free tube and acid-washed or metal-free container. Contamination can falsely raise results. The lab may reject the sample if the wrong tube, anticoagulant, temperature, or container is used.
Recent diet matters, but ordinary iodine intake usually causes smaller changes than contrast dye, kelp, or iodine medication. Eating fish the night before testing is less likely to explain a marked high blood iodine result than taking iodine drops or having contrast imaging. Seaweed is the exception because iodine content varies enormously by type; kelp and kombu can contain far more iodine than nori.
Biotin is often discussed with thyroid testing because it can interfere with some immunoassays. Biotin is not the main concern for iodine measurement by ICP-MS, but it can affect related thyroid labs at some laboratories. If TSH, free T4, free T3, or thyroid antibodies are being checked at the same time, ask whether you should pause high-dose biotin before testing.
Next Steps After Abnormal Results
An abnormal iodine blood result should lead to a structured review, not guesswork. The next step depends on the degree of abnormality, symptoms, thyroid history, pregnancy status, and whether there was a clear exposure.
For a low iodine result, useful follow-up may include:
- Review the lab range, specimen type, and units.
- Check diet patterns, including iodized salt, dairy, seafood, eggs, and fortified foods.
- Review pregnancy, breastfeeding, or fertility plans.
- Check TSH and free T4, and sometimes free T3.
- Consider urinary iodine testing if intake status is unclear.
- Review other thyroid-related nutrients when clinically relevant.
- Correct intake with food or standard-dose supplements rather than high-dose iodine unless specifically prescribed.
For a high iodine result, useful follow-up may include:
- Identify contrast imaging, amiodarone, kelp, iodine drops, and thyroid support products.
- Stop nonessential high-iodine supplements after discussing the result with a clinician.
- Check TSH, free T4, and sometimes free T3 to look for thyroid effects.
- Repeat iodine testing only after enough time has passed for the exposure pattern to change.
- Monitor more closely if there is Hashimoto’s disease, Graves’ disease, thyroid nodules, pregnancy, newborn exposure, or older age.
- Review kidney function if iodine remains high without a clear source.
Daily intake targets can help put results in context. For many adults, the recommended iodine intake is 150 mcg/day. During pregnancy, the U.S. recommended intake is 220 mcg/day, and during lactation it is 290 mcg/day. Some international guidance uses 250 mcg/day during pregnancy and lactation. These are intake targets, not blood test targets.
The adult upper intake level is 1,100 mcg/day from food and supplements for most adults. This limit does not apply to people receiving iodine for medical treatment, such as certain thyroid or radiation-related indications, but those situations require clinician supervision. Long-term supplement use above the upper limit increases the chance of thyroid problems, especially in susceptible people.
Food-based correction is often safer than large iodine doses. Good iodine sources include iodized salt, cod, seafood, milk, yogurt, eggs, and some breads made with iodate dough conditioners. Many specialty salts are not iodized. Many plant-based milk alternatives contain little iodine unless fortified. Seaweed can be helpful in small amounts, but kelp products are unpredictable and can overshoot intake by a wide margin.
A result within range does not always end the evaluation. If thyroid symptoms persist, the focus should shift to thyroid function, autoimmune thyroid disease, medication effects, pituitary causes, anemia, sleep, heart rhythm, inflammation, or other nutrient issues. Iodine is one piece of thyroid health, not the whole picture.
References
- Iodine – Health Professional Fact Sheet 2024 (Official Fact Sheet)
- IOD – Overview: Iodine, Serum 2025 (Lab Test Directory)
- Iodine, Serum/Plasma 2026 (Lab Test Directory)
- Iodine deficiency 2026 (Official Reference)
- Serum iodine reference ranges and their correlations with urinary iodine and thyroid function: A systematic review and meta-analysis 2025 (Systematic Review)
- Serum iodine concentration and its associations with thyroid function and dietary iodine in pregnant women in the southeast coast of China: a cross-sectional study 2023 (Cross-Sectional Study)
Disclaimer
An iodine blood test should be interpreted by a qualified healthcare professional, especially during pregnancy, breastfeeding, thyroid disease, kidney disease, or amiodarone treatment. Do not start high-dose iodine or stop prescribed medication based only on one iodine result. Seek urgent medical care for severe palpitations, chest pain, fainting, confusion, or serious breathing symptoms.
