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

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.