Effects of geographical factors on reference values of the thyroid stimulating hormone in healthy adults in China and its clinical significance.

The thyroid stimulating hormone (TSH) plays an important regulatory role in maintaining normal function of the thyroid gland. The purpose of this study was to explore the geographical, spatial distribution of TSH normal values in healthy Chinese adults to be used for the formulation of a standard reference. TSH values of 9321 healthy adults from 120 cities in China were collected together with 24 topographic, climatic and soil variables and used for the determination of spatial, significant relationships between TSH and these geographical factors by correlation analysis. Eleven significant factors were extracted and subjected to ridge regression and construction of vector machine models. The predicted values were tested for normality, with the disjunctive Kriging interpolation method used for geographical distribution. The values found showed a spatial pattern of higher values in the North and west but lower in the South and east We concluded that ridge regression models are useful for this kind of investigations and that certain geographical factors determine the level of TSH in healthy adults in a large expanse of land where topography, climate and soil indices vary.