Classification of thyroid size by palpation and ultrasonography in field surveys

Background Goitre surveys are used to assess the degree of iodine deficienc y in a population. The change of goitre classification made by WHO in 1994 implied that a smaller thyroid size should be regarded as goitre. Furthermo re, the acceptable goitre prevalence was lowered from 10% to 5%, and ultras onography 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 ultrasonographic examination. Methods We studied 225 schoolchildren (aged 7-14 years) in a highland villa ge in Tanzania. The size of the thyroid was assessed in duplicate by ultras onography and by WHO's 1960 and 1994 palpation systems. The latter were don e by three examiners. Variations within and between examination methods and examiners were assessed. and measurement errors by ultrasonography were as sessed 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 "tr ue" 5% prevalence. Findings The lowered criterion for goitre resulted in an extra 20-33% of ch ildren 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 lob es. The new goitre criterion decreased specificity from 76% to 29%, whereas sensitivity rose from 56% to 80%. In contrast, a suggested sharpening of t he 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 palp ation goitre prevalence of 10% can allow affordable monitoring of thyroid s ize through palpation in field surveys.