Background: Goitre surveys are used to assess the degree of iodine deficiency in a population. The change of goitre classification made by WHO in 1994 implied that a smaller thyroid size should be regarded as goitre. Furthermore, the acceptable goitre prevalence was lowered from 10% to 5%, and ultrasonography was recommended as a more precise method for diagnosis of goitre. We studied the effects of the change of palpation system, and compared the precision of the old and new systems with that of ultrasonographic examination.
Methods: We studied 225 schoolchildren (aged 7-14 years) in a highland village in Tanzania. The size of the thyroid was assessed in duplicate by ultrasonography and by WHO's 1960 and 1994 palpation systems. The latter were done by three examiners. Variations within and between examination methods and examiners were assessed, and measurement errors by ultrasonography were assessed from duplicate examinations. The sensitivity and specificity of the two palpation systems were calculated, with diagnosis by ultrasonography as the gold standard. Apparent palpation prevalences were calculated at a "true" 5% prevalence.
Findings: The lowered criterion for goitre resulted in an extra 20-33% of children being diagnosed as having goitre by palpation. The variation between repeat examinations was only slightly smaller by ultrasonography (kappa=0.63) than by experienced examiners (kappa=0.57-0.58). The variation between thyroid volume estimation by ultrasonography and the true volume was about 50% due to both measurement error and variation in the shape of thyroid lobes. The new goitre criterion decreased specificity from 76% to 29%, whereas sensitivity rose from 56% to 80%. In contrast, a suggested sharpening of the old criterion increased specificity to 90%.
Interpretation: A return to the old (1960) palpation criterion for goitre: "lobes larger than the terminal phalanxes of thumbs" and to an accepted palpation goitre prevalence of 10% can allow affordable monitoring of thyroid size through palpation in field surveys.