Inadequacy of the WHO classification of the thyroid gland.

In order to evaluate the reproducibility of the WHO classification of goitre, the observer variation was estimated as kappa coefficients. Three observers independently inspected and palpated the thyroid gland of 53 patients twice and assessed the thyroid according to the five grades of the WHO classification. The thyroid volume was also measured by ultrasonography. We found kappa values from 0.15 to 0.70 in the interobserver study, and from 0.02 to 0.89 in the intraobserver study. Considerable overlap between the five grades was demonstrated when the assessments were related to volume estimated by ultrasonography. Description of the thyroid gland according to the WHO classification is inaccurate and not reproducible and is therefore of limited value.