Evaluation of a mass spectrometry-based method for estradiol determination in girls with benign premature thelarche - a method comparison with extraction RIA.

INTRODUCTION: Premature thelarche in girls younger than 4 years of age is a cause for clinical concern and requires reliable assessment tools. Current guidelines, for decision-making and management of girls with premature thelarche in Sweden are based on serum estradiol determination performed by sensitive extraction radioimmunoassay (RIA). However, the extraction RIA has been replaced by a high-sensitivity mass spectrometry (MS)-based estradiol method. The primary aim of the present study was to evaluate the performance of the MS-based method in comparison with extraction RIA. METHODS: In a prospective observational study, 43 serum samples from girls with premature thelarche aged 6-48 months were run in parallel for comparison between the phased-out extraction RIA and the newer high-sensitivity MS-based assay. The lower limits of detection were 4 pmol/L for both methods. RESULTS: There was a significant correlation between the two methods, r=0.67, p=0.000. The MS-based method yielded a mean of 5.3 (±2.7) pmol/L lower concentrations compared to extraction RIA. CONCLUSION: The estradiol upper limit level for what is considered benign in premature thelarche, obtained with extraction RIA, needs to be lowered when analyzed with high sensitivity MS-based methods.