Impacto del empleo de umbrales específicos de referencia en el diagnóstico de las alteraciones funcionales tiroideas en la mujer gestante

Abstract

Objective

To determine trimester- and assay-specific reference intervals for thyroid hormones during pregnancy, and the impact of using non-specific intervals on the diagnosis of functional disorders in the first trimester.

Methods

A total of 759 healthy pregnant women older than 18 years with uncomplicated single intrauterine gestations and attending Primary Care Centres were consecutively recruited from January 2014 to September 2014. After excluding women who did not complete the follow-up during pregnancy, and those with functional thyroid disorders or with thyroid-specific autoantibodies, a total of 411 pregnant women were selected as the reference population. TSH, FT4, and FT3 were measured in each trimester using electrochemiluminescence immunoassay, and urinary iodine concentration was measured in the first and in the third trimester using high performance liquid chromatography.

Results

The TSH reference intervals expressed as median and 2.5-97.5 percentiles were: 1.53 μIU/ml (0.26-3.95), 1.90 μIU/ml (0.78-3.85) and 1.89 μIU/ml (0.71-3.61) in first, second and third trimesters, respectively. The median urinary iodine concentration (UIC) was 171.31 μg/l (90.7-274.9) in the first trimester and 190.37 μg/l (96.44-360.38) in the third. Interpretation of thyroid function tests using non-local-pregnant reference intervals would result in misclassification of the thyroid function in a significant percentage of pregnant women (19.8% with the proposed international specific reference intervals, and 8.52% with the non-specific reference intervals of our assay).

Conclusions

The use of non-local reference intervals for the diagnosis of thyroid disorders during pregnancy could lead to a large number of misclassified results, contributing to sub-optimal patient care.