What is the first recommended test to order for checking iodine deficiency?

Testing for Iodine Deficiency

The gold standard for assessing iodine status is 24-hour urinary iodine excretion, which should be the first test ordered to check for iodine deficiency. 1

Primary Assessment Methods

24-Hour Urinary Iodine Collection

• Gold standard method for assessing iodine status
• Reference values: 100-300 μg/24hr
• Values <100 μg/24hr indicate deficiency 1
• Provides the most accurate reflection of iodine intake

Alternative Testing Options

1. Spot Urine Iodine Concentration with Creatinine Correction

   • More practical when 24-hour collection is difficult
   • Should be scaled to creatinine (est24h-UIEcrea) for better accuracy
   • Significantly better correlation with true 24-hour excretion than uncorrected spot samples 2

2. Thyroid Function Tests

   • TSH, T4, and T3 measurements
   • Recommended for monitoring patients on long-term parenteral nutrition 3
   • Important caveat: TSH alone is not a sensitive indicator of iodine status, as concentrations often remain normal despite frank iodine deficiency 1

Testing Considerations

When to Test

• Populations with high prevalence of thyroid disorders 3
• Pregnant women (increased iodine requirements)
• Patients on long-term parenteral or enteral nutrition 3, 1
• Children in areas with known iodine deficiency

Field Testing Options

When laboratory resources are limited:

• Rapid Urinary Iodide Test (RUIT) - a semi-quantitative method with 96% sensitivity compared to standard methods 4
• Filter paper methods for dried urine collection - convenient for remote areas without refrigeration 5

Interpretation and Follow-up

Interpretation Guidelines

• Deficiency: <100 μg/24hr in 24-hour urine collection
• Normal range: 100-300 μg/24hr
• Serum iodine reference range: 40-100 μg/L 1

Common Pitfalls to Avoid

1. Relying solely on TSH measurements

   • TSH may remain normal despite significant iodine deficiency 1

2. Using uncorrected spot urine samples

   • Uncorrected spot samples correlate poorly with true 24-hour excretion 2

3. Overlooking special populations

   • Pregnant women, children, and patients on artificial nutrition have higher requirements and need careful monitoring 1

4. Ignoring potential contamination sources

   • Recent exposure to iodinated contrast media, topical iodine disinfectants, or medications like amiodarone can affect test results 3

By following these evidence-based testing approaches, clinicians can accurately identify iodine deficiency and implement appropriate interventions to prevent associated morbidity and mortality.