ESPE Abstracts

Objectives: In laboratory medicine, external quality assessment (EQA) schemes have become versatile tools for the detection of analytical flaws. However, for pediatric sex steroid levels EQA schemes are lacking. We aimed to investigate the suitability of different estradiol and testosterone immunoassays in a pediatric setting, in comparison with clinical liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays.

Methods: The study was conducted by staff and the advisory group of endocrinology at Equalis, the Swedish provider of EQA schemes for laboratory medicine. Test material consisted of five pooled serum samples from children either prepubertal or in early puberty. Clinical laboratories enrolled in Equalis EQA schemes for estradiol and testosterone were invited to participate as well as clinical laboratories using LC-MS/MS-assays. Samples were analyzed by either commercial immunoassays (n=18) or in- house LC-MS/MS assays (n=3).

Results: For estradiol, LC-MS/MS assays showed a high degree of conformity with interlaboratory coefficients of variation (CV:s) below 24.2%. Reported levels were (mean±SD); 4.9±1.2; 8.5±1.3; 9.4 ±1.0; 16.6±0.6 and 33.9±1.6 pmol/L (group mean±standard deviation). The direct immunoassays had lower precision, their interlaboratory CV:s were up to 81.4%. Reported concentrations were 25.3±18.1; 32.6±25.3; 27.6±18.8; 32.8±26.7 and 45.7±19.4 pmol/L, a clear overestimation compared to LC-MS/MS. Testosterone LC-MS/MS also showed a high degree of conformity, CV:s were below 13.4%, and reported concentrations were 0.06±0.00; 0.19±0.02; 0.62±0.08; 0.99±0.11 and 1.00±0.11 nmol/L. The direct immunoassays had larger discrepancy between results; CV:s were up to 95.8%, with corresponding concentrations 0.12±0.11; 0.11±0.05; 0.46±0.12; 0.80±0.28 and 0.85±0.23 nmol/L. Both under- and over-estimation occurred.

Conclusions: This study enabled some general conclusions to be drawn for samples from children. a) Commercially available estradiol immunoassays are not suitable for diagnosis in children. b) Commercially available testosterone immunoassays have an uncertainty of reproducibility in the low range that each individual user should consider. c) For safe diagnosis and determination of sex steroids in children, analysis with MS/MS-based methods is recommended. d) Every pediatric endocrinologist or laboratory scientist should be familiar with the pitfalls of their sex steroid methods used.