Data sources and inclusion criteria for the Database on Iodine Deficiency
Survey reports and publications reporting on goitre and/or urinary iodine are collected/requested from:
- Ministries of Health through WHO regional and country offices.
- National research and academic institutions.
- Nongovernmental organizations.
- Organizations of the United Nations system.
- Regular searches of online databases, such as PubMed, Medline, Ovid, Embase, and WHO regional databases (African Index Medicus, Index Medicus for the WHO Eastern Mediterranean Region, Latin American and Caribbean Center on Health Sciences Information, Pan American Health Organization Library Institutional Memory Database, Index Medicus for South-East Asia Region).
Data inclusion criteria
Survey data are extracted and included in the database only from complete original survey reports and publications that provide details of the sampling methods. Data from all administrative levels and all population groups cited are included. Studies must have a population-based sample frame and must use standard UI and TGP measuring techniques1.
To be included, a survey must report on at least one of the following criteria:
- Goitre* prevalence investigated by palpation and classified according to WHO recommendations.
- Grade 1: A goitre that is palpable but not visible when the neck is in the normal position, even when the thyroid is not visibly enlarged. Thyroid nodules in a thyroid, which is otherwise not enlarged, fall into this category.
- Grade 2: A swelling in the neck that is clearly visible when the neck is in a normal position and is consistent with an enlarged thyroid when the neck is palpated.
* A thyroid gland will be considered goitrous when each lateral lobe has a volume greater than the terminal phalanx of the thumbs of the subject being examined.
Only TGP data measuring goitre by palpation are included. Until recently, no international reference values for thyroid size in iodine-replete populations measured by ultrasonography were available, and thus results from surveys using this technique have not yet been included2.
- Urinary iodine (UI) reported by at least one of the following categories:
- Distribution: The percentage of the population falling within the categories <20 µg/L, 20-49 µg/L, 50-99 µg/L, 100-299 µg/L, >300 µg/L.
- Prevalence: The percentage of the population falling below the cut-off level of 100 µg/L.
- Median and/or mean (µg/L, µg/g creatinine or µg/24h).
When a potentially relevant survey is identified and the full report obtained, all data are checked for consistancy as part of routine quality control. When necessary, the authors are contacted for clarification or additional information. Final data are extracted and entered into a standard data form. The full archived documentation and correspondence are available to users on request.
- World Health Organization, United Nation Children's Fund, International Council for Control of Iodine Deficiency Disorders. Assessment of the iodine deficiency disorders and monitoring their elimination. Geneva: World Health Organization; 2001. WHO document WHO/NHD/01.1.
- Zimmermann MB, Hess SY, Molinari L, de Benoist B, Delange F, Braverman LE et al. New reference values for thyroid volume by ultrasound in iodine-sufficient schoolchildren: a World Health Organization/Nutrition for Health and Development Iodine Deficiency Study Group Report. American Journal of Clinical Nutrition 2004;79: 231-237.