Thyroid analytes TSH, FT3 and FT4 in serum of healthy elderly subjects as measured by the Roche modular system: do we need age and gender dependent reference levels?

BACKGROUND: Age and gender may be involved in the regulation of TSH and thyroid hormones. Reliable investigations concerned with the matter of whether or not these factors are of importance for diagnostic evaluation of the thyroid function are scarce. We used serum values of the CARLA study to calculate reference intervals for TSH, FT3, and FT4 and examine these parameters for their association with age or gender. METHODS: The CARLA study included 967 men and 812 women aged 45 to 83 years. We defined a reference group of 1002 subjects that were free of thyroid disease for data analysis by laboratory analysis and questionnaire, calculated age-dependent moving percentiles (2.5th/97.5th) for TSH, FT4, and FT3 and tested this data set for the confounding factors age and gender. Thereafter, the results were compared to data from the Leipzig Blood Donor study established in 2005. RESULTS: TSH (significant in trend (p = 0.064)) and FT3 (p = 0.001) were inversely associated with age. The correlation of FT3 with age was furthermore influenced by gender (p < 0.001). Neither gender nor age influenced values of FT4. CONCLUSIONS: The decreased TSH and FT3 levels with increasing age suggest a diagnostically relevant modification in the feed back regulation of thyroid function of the elderly. FT3 data should thus be interpreted gender-dependent and even age-dependent for males. These findings should be considered for the diagnostic examination of older patients with suspected disorders of thyroid function.