Iodine (Urine, Spot / 24h)
Urinary iodine measures how much iodine your body is excreting, usually from a spot or 24-hour urine sample. Because most iodine you take in leaves through urine, this reflects your recent iodine intake.
Iodine is essential for making thyroid hormones, which regulate metabolism, growth, and development. Urine is used to assess iodine because blood levels are less informative for day-to-day intake. Individual urine tests vary with recent meals, so iodine status is best understood across a population or with repeated sampling.
A high urinary iodine reflects high recent intake, often from supplements, certain foods like seaweed, or iodine-containing medications or contrast dyes. Excess iodine can disturb thyroid function in susceptible people, so a very high value may warrant review. A single measurement reflects recent intake rather than long-term status.
A low urinary iodine suggests recent intake has been limited, which over time can affect thyroid hormone production. It is more likely with low-dairy, low-seafood, or non-iodized-salt diets.
Because single samples vary, urinary iodine is interpreted cautiously and often alongside thyroid tests. A clinician can help you understand your result, especially in pregnancy when iodine needs rise.
Sources
Educational context only, not medical advice or a diagnosis. Reference ranges vary by lab, age and sex; always discuss your results with a clinician.