Toward a consensus on reference values for thyroid volume in iodine-replete schoolchildren: results of a workshop on interobserver and inter-equipment variation in sonographic measurement of thyroid volume

Objective: Interpretation of thyroid ultrasonography for assessing goiter p revalence requires valid reference criteria from iodine-sufficient populati ons. Reports have suggested the current reference criteria for thyroid volu me (T-vol) of WHO/ICCIDD (International Council for the Control of Iodine D eficiency Disorders) may be too high. Our objective was to determine if int er-observer and/or inter-equipment variability contributes to the disagreem ent in sonographic T-vol in children reported from iodine-sufficient areas. Design: A 2-day workshop in which four experienced ultrasound examiners fro m around Europe measured T-vol in 45 6-12-year-old Swiss schoolchildren usi ng four different portable ultrasound machines. One of the participating ex aminers (observer A) had generated the T-vol data in European children that are the basis for the WHO/ICCIDD reference criteria, Methods: Sonographic T-vol was measured in each child by all four examiners on all four machines. Six hundred and eighty-four examinations were comple ted, with examiners having no knowledge of one another's results. Inter-obs erver and inter-equipment variation was calculated, Results: Mean inter-equipment variation in T-vol was 15.2% (95% CI: 14.1, 1 6.3%), There were no significant differences in T-vol between equipment (P = 0.51). For all observers, the mean interobserver variation in T-vol was 2 5.6% (95% CI: 23.9, 27.2%). At all ages and all body surface areas, there w as a large systematic measurement bias (+30% volume) between the mean T-vol of observer A and the mean T-vol of observers B, C and D. Reanalysis using data from observers B, C and D reduced the mean inter-observer variation i n T-vol to 13.3% (95% CI: 11.9, 14.7%). A correction factor for the systema tic difference of operator A for the P50 and P97 of T-vol was estimated usi ng analysis of covariance. When applied to the WHO/ICCIDD reference data, i t sharply reduced the discrepancy between the WHO/ICCIDD criteria and those from other iodine-sufficient children around the world. Conclusions: Inter-equipment error contributes minimally to reported differ ences in sonographic T-vol. Even among experienced examiners, inter-observe r variation in sonographic T-vol in children can be high, and probably cont ributes to the current disagreement on normative values in iodine-sufficien t children. A systematic bias at least partially explains why the WHO/ICCID D reference data differ from those reported from other iodine-sufficient ch ildren around the world. The findings argue strongly for the standardizatio n of methods used for sonographic measurement of T-vol in children.