Once known the sensitivity and specificity of the direct radioassay (DR) techniques were measured antithyroid antibodies (AAT) by this method in pediatric patients that consulted by different motives to discard presumed thyroid pathology.

Objective: 1.-To establish cut criteria expressed in KU/l for TPO-Ab and TG-Ab in euthyroid patients (EU). 2.-To establish their usefulness in the clinical diagnosis, through frequency analysis of positiveness(F+) by functional state and by thyroid pathology.

Material and Methods: 439 pat. (0.01-18y, F:65%, M:35%) classified according to functional state to the moment of the test and thyroid final diagnosis. They were effected studies of ecograffa thyroid, scanning with Tc99 or I131. There were dosed AAT by RD: TPO-Ab and TG-Ab, T3, T4, T4L by RIA, TSH and Test of TRH by IRMA. The correlation measures were studied through coefficient of Spearman or Phi (for binary variables). The cut criteria were established by studies of the frequencies distribution and the comparisons of prevalence of positiveness by analysis of contingency tables.

Results: The association among TPO-Ab and TG-Ab with chronological age showed a low correlation being in EU of 0.13 and 0.07 respect. The distribution of TPO-Ab in EU suggested a value of cut of 0.46 UK/l (P95) and of 0.30 UK/l (P95) for TG-Ab, which was below that ones found according to the euthyroid functional to the moment of the test. It was observed clear association among goiter and TPO-Ab+ (68% for goiter and 42% in the without goiter, p<0.01). TG-Ab it was positive in 50% of goiter vs 17% in the patients without goiter (p< 0.001). The prevalence of positiveness in diffuse goiters was positively correlated with the degree of goiter for both AAT. The clinic or subclínical condition of the hypothyroidism was associated to the presence of AAT by TPO-Ab (73% and 49.5% resp.) and TG-Ab(46% and 28% resp.). It was demonstrated a meaningful association among TPO-Ab and TG-Ab (p< 0.001) even though the correspondence among both was not high(Phi=0.44). The total discrepancy was 29% (25% for TPO-Ab+ vs TG-Ab-). Among the etyological diagnoses is underlined the pure autoimmunity with discrepancy(TPO-Ab + and TG-Ab-) of 68% and in autoimmune thyroiditis disease of 35%.

Conclusions: The low correlation among TPO-Ab, TG-Ab and age would not justify the search of a cut criterion with age correction for pediatric patients. The cut criterion for TPO-Ab and TG-Ab in base to the final diagnosis was more reasonable than the one based on the functional state. The condition of positiveness was not independent of the functional state or of the ethiology. Our results show that TPO-Ab would be the best marker of pure autoimmunity and of autoimmune thyroiditis disease. Nevertheless the determination of both AAT increases the detection probability of autoimmunity.