Determination of a trivariate reference region for free thyroxine index, free triiodothyronine index, and thyrotropin from results obtained in a health survey of middle-aged women.

Abstract

Abstract We measured free thyroxine index, free triiodothyronine index, and thyrotropin in serum in a community survey of the female population 39--60 years old. A statistical method using Mahalanobis' distance was applied to the data, to identify and eliminate highly abnormal values, "outliers." There was a small but statistically significant increase in each of the three hormones with age. After correction for age dependency, significant but rather small correlations were found between the hormones. The material was used to calculate univariate reference intervals and a trivariate 0.95-tolerance region.