Evaluation of the ADVIA Centaur TSH-3 assay

Nomogram-based evaluation of thyroid function in appropriate-for-gestational-age neonates in intensive care unit

OBJECTIVE

The objective of this study was to help neonatologists to interpret the thyroid hormone results accurately, and also to provide reference ranges and/or nomograms of FT4 (free thyroxine) and thyrotropin against gestational age at postnatal 1 week and 1 month in order to assess thyroid function in AGA (appropriate for gestational age) neonates in intensive care unit.

STUDY DESIGN

This is a retrospective study. We included a total number of 515 AGA neonates between 24 and 42 weeks of gestation. Routine results of serum FT4 and TSH that had been analyzed with an immunoassay were collected from existing laboratory data. Least square regression analyses were used to estimate both the mean and the s.d. curves as polynomial functions of gestational age.

RESULT

Free T4 levels were correlated with gestational age both at postnatal 1 week (r=0.39, P<0.001) and 1 month (r=0.26, P<0.001). Serum TSH levels at postnatal 1 week and 1 month did not show any correlation with gestational age. Scatterplots of FT4 levels against gestational age at 1 week and 1 month, showing the predicted 2.5th, 50th and 97.5th percentiles and central 95% reference ranges for TSH were provided.

CONCLUSION

Gestational age-specific nomograms for FT4 and reference ranges for TSH at postnatal 1 week and 1 month in AGA neonates have been developed. This can help neonatologists to interpret the thyroid hormone results accurately. Further studies providing reference ranges/nomograms for thyroid function in small-for-gestational-age neonates are needed.

Pediatric reference intervals for thyroid hormone levels from birth to adulthood: a retrospective study

BACKGROUND

Age- and sex-specific reference intervals are an important prerequisite for interpreting thyroid hormone measurements in children. However, only few studies have reported age- and sex-specific pediatric reference values for TSHbasal (TSH), free T3 (fT3), and free T4 (fT4) so far. Reference intervals are known to be method- and population-dependent. The aim of our study was to establish reference intervals for serum TSH, fT3, and fT4 from birth to 18 years and to assess sex differences.

METHODS

2,194 thyroid hormone tests obtained from a hospital-based pediatric population were included into our retrospective analysis. Individuals with diagnoses or medications likely to affect thyroid function were primarily excluded, as well as the diagnostic groups, if different from the purely healthy subgroup (n = 414). Age groups were ranging from 1 day to 1 month, 1 - 12 months, and 1 - 5, 6 - 10, 11 - 14, and 15 - 18 years, respectively. Levels of fT3, fT4 and TSH were measured on Advia(R) Centaur automated immunoassay system.

RESULTS

The final sample size for reference data creation was 1,209 for TSH, 1,395 for fT3, and 1,229 for fT4. Median and 2.5/10/25/75/90/97.5 percentiles were calculated for each age group. Males had greater mean fT3 concentrations than females (p < 0.001). No sex-differences were found for TSH and fT4 between age-matched serum samples. Median concentrations of fT3, fT4 and TSH were greatest during the first month of life, followed by a continuous decline with age.

CONCLUSION

Our results corroborate those of previous studies showing that thyroid hormone levels change markedly during childhood, and that adult reference intervals are not universally applicable to children. Moreover, differences of our reference intervals compared to previous studies were observed, likely caused by different antibody characteristics of various analytical methods, different populations or undefined geographic covariates, e.g. iodine and selenium status.

Continuous age-dependent reference ranges for thyroid hormones in neonates, infants, children and adolescents established using the ADVIA Centaur Analyzer

In neonates, infants, children and adolescents serum concentrations of the thyroid hormones show a clear age dependency. Currently, age-dependent thyroid hormone reference ranges for the new ADVIA Centaur immunoanalyzer are not available. Thyroid-stimulating hormone (TSH), free thyroxine (FT4), total thyroxine (T4), free triiodothyronine (FT3) and total triiodothyronine (T3) were determined in the sera of 460 healthy children aged 0 daysto 18 years from an inland (n=308) and a seaside city (n=152) using the Bayer ADVIA Centaur analyzer. Square root functions defining the upper and lower limit of the continuous age-dependent reference range and the median line for each thyroid hormone were estimated applying a parametric regression technique. Continuous age-dependent reference ranges show a better fit to the obtained data than discontinuous reference ranges. The median TSH and FT4 concentrations decrease within the first year of life and are nearly constant until 18 years of age. The median T4 decreases within the entire age interval, whereas the median FF3 is constant. The median T3 increases within the first year of life and decreases afterwards. The calculated continuous reference ranges for T4, T3 and partly FT4 are consistent with published reference ranges. However, the reference ranges obtained for FT3 and partly TSH differed considerably, compared to published reference ranges. No significant residence- or sex-specific effects on age-adjusted hormone concentrations were found except for a slight residence-specific effect on age-adjusted FT4, which was probably due to assay imprecision. Due to the lack of international standardization, the assay-specific evaluation of reference ranges is very important. Continuous age-dependent reference ranges comply better with the biological reality and are more reliable than discontinuous reference ranges.