Importance of total and measured free testosterone in diagnosis of male hypogonadism: immunoassay versus mass spectromet
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ORIGINAL ARTICLE
Importance of total and measured free testosterone in diagnosis of male hypogonadism: immunoassay versus mass spectrometry in a population of healthy young/middle‑aged blood donors P. Agretti1 · C. Pelosini1 · L. Bianchi1 · A. Del Grosso1 · A. Saba2,3 · D. Canale4 · M. R. Sessa1 Received: 12 February 2020 / Accepted: 20 May 2020 © Italian Society of Endocrinology (SIE) 2020
Abstract Purpose To meet clinicians’ request for adequate results and reliable reference ranges for testosterone, this study was planned with the aims (i) to verify the reliability of the reference interval for total testosterone (TT) declared by immunoassay manufacturer and adopted by laboratory, (ii) to compare results for serum TT obtained by immunoassay and LC–MS/MS and (iii) to verify if the cutoff values for low TT and measured free testosterone (FT), defined by Endocrine Society Guidelines for diagnosis of hypogonadism, are applicable to our study group. Methods Sera from anonymous young/middle-aged male blood donors were selected for the study. TT was measured by immunoassay and LC–MS/MS. SHBG was measured by immunoassay and used with albumin concentration to calculate FT according to Vermeulen’s formula. Results The reference interval declared by the manufacturer and adopted by the lab was validated. The two methods for TT evaluation correlated very well. TT and FT lower limits at 5th and 2.5th percentile are below the cutoffs reported in the literature for the diagnosis of hypogonadism. Conclusions The immunoassay currently used in our lab can be considered an adequate tool for TT, but it’s essential that clinical data agree with the biochemical ones, particularly in the presence of TT values between the lower limit of reference range and the cutoff values recommended by scientific societies. Keywords Testosterone · Hypogonadism · Immunoassay · Mass spectrometry · Men healthy donors
Introduction Testosterone is the main male sex hormone that regulates fertility, muscle mass, fat distribution, and red blood cell production. It is primarily secreted by testicular Leyding cells and to a lesser extent by adrenal cortex, and its * P. Agretti p.agretti@ao‑pisa.toscana.it 1
Laboratory of Chemistry and Endocrinology, University Hospital of Pisa, Via Paradisa 2, 56124 Pisa, Italy
2
Department of Surgical, Medical and Molecular Pathology and Critical Care Medicine, University of Pisa, Via Savi 10, 56126 Pisa, Italy
3
Laboratory of Clinical Pathology, University Hospital of Pisa, Via Roma 67, 56126 Pisa, Italy
4
Endocrinology Unit, University Hospital of Pisa, Via Paradisa 2, 56124 Pisa, Italy
production is regulated by hypothalamus-pituitary-gonad axis negative feedback. Most circulating testosterone is tightly bound to sex-hormone-binding globulin (SHBG), a minor fraction is weakly bound to albumin and a small amount exists as free hormone. Albumin-bound testosterone dissociate freely in capillary blood becoming readily available for tissue uptake. For this reason, free testosterone and albumin-bound
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