AbstractEstablishment of reliable reference intervals remains valuable for confirming validity and advancing standardization across methods and populations. Moreover, knowledge of the measurement uncertainty (U) and of the reference change value (RCV) has important applications in clinical chemistry.Starting from the information available in the laboratory data base (29,901 subjects) an initial selection was carried out by eliminating all subjects with a clinical or laboratory pathological report; data from 7581 0- to 20-year-old subjects (53.87% girls) remained in the study. These subjects, divided into nine age groups, were used to define reference distribution percentiles (2.5th, 50th and 97.5th) of serum thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4), and free T4 (fT4), as well as U and RCV of these assays.In early infancy, T4 and fT4 values were higher than in the older age groups. Serum T4 95th percentile reference value, useful for the diagnosis of hyperthyroidism, was 142.9 in 20-year-old boys and 230.4 nmol/L in early infants and serum T3 95th percentile was 2.6 and 3.5 nmol/L, respectively, while fT4 2.5th percentile reference value, useful for the diagnosis of hypothyroidism, was 9.6 and 13.0 pmol/L, respectively. Serum TSH 97.5th percentile showed less age variation, 4.38–4.88 mIU/L. Performance of the four assays resulted in approximately 20% Us, reflecting simple and complex imprecision, trueness, analytical and functional sensitivity. RCV of serum TSH (58.6%) was larger than for thyroid hormones (28.3%–34.7%), probably due to the high biological variation of this hormone.We have established reference interval for TSH and thyroid hormones, as well as Us for assessing reliability of measurements, and RCVs to alert users on the presence of clinical significant changes.

Serum IGF-I and IGFBP-3 assays are used to monitor rhGH treatment. Some discrepancies in results obtained by means of different assays have been reported. The aim of this study was to establish normal ranges for circulating IGF-I and IGFBP-3 in children and adolescents of Hispanic and Italian origin. Circulating levels of IGF-I and IGFBP-3 were measured in 169 Hispanic and Italian prepubertal children and 66 adolescents of both sexes, using a chemiluminescent assay. Serum levels of IGF-I and IGFBP-3 increased from early childhood into adolescence. After pubertal peaks of IGF-I and IGFBP-3, slight decreases were observed with increasing age. Furthermore, serum IGF-I levels were significantly higher in girls than in boys, suggesting a sexual dimorphism in serum IGF-I values in late prepuberty and early puberty. Differences in IGF-I and IGFBP-3 absolute values between our study and previous studies suggest the need to establish reference ranges for each ethnic group.

Presentación de casos clínicos RESUMEN El síndrome de Guillain-Barré constituye una entidad de etiología diversa, que se caracteriza por debilidad muscular aguda, simétrica, ascendente y progresiva, y es una de las polineuropatías adquiridas más frecuentes en la infancia. Entre los diagnósticos diferenciales, deben considerarse las neuropatías producidas por metales pesados, mercurio y plomo, y metaloides, como el arsénico, plaguicidas organofosforados y el tetracloruro de carbono. Se presenta a un paciente de 14 años con diagnóstico de síndrome de Guillain-Barré sin respuesta al tratamiento convencional con gammaglobulina. Considerando otras etiologías, se sospechó neuropatía producida por metales pesados, y se confirmó intoxicación por mercurio. El objetivo de esta presentación es concientizar a los pediatras acerca del impacto de los tóxicos ambientales en la salud infantil para realizar un diagnóstico precoz pesquisando datos clave a través de la historia clínica ambiental. Palabras clave: polineuropatías, intoxicación del sistema nervioso por mercurio, historia clínica ambiental.

Introduction. Due to the heavy industrialization of the Autonomous City of Buenos Aires and Greater Buenos Aires, the population may have become exposed to metals. To assess the level of exposure to chromium and mercury in children, it is critical to have local reference values (RVs). Our objective was to determine pediatric RVs for chromium and mercury in a single urine sample. Population and methods: Children who were not exposed to the studied contaminants and who attended the Department of Low Risk Conditions and the Daycare Center Office of Hospital de Pediatría S.A.M.I.C. "Prof. Dr. Juan P. Garrahan" were included. Urinary chromium (UCr), urinary mercury (UHg), and urinary creatinine were measured. The p95 and its corresponding 95 % confidence interval (CI) were estimated based on the RV concept proposed by the German Human Biomonitoring Commission. Results: The study included 160 patients. A total of 144 samples from children aged 1-17 years (median: 7 years) were collected. UCr was measured in 137 samples and UHg, in 129 samples. The median value of chromium was 0.54 µg/g of creatinine (range, undetectable to 3.06), while that of mercury was 0.49 µg/g of creatinine (range, undetectable to 7.57). Conclusions: The RVs for UCr were up to 1.5 µg/L [1.2-2.8] and up to 2.2 µg/g of creatinine [1.8-3.0], and for UHg, up to 2.5 µg/L [1.8-4.8] and 3.2 µg/g of creatinine [2.5-4.7].