• Rui V Duarte, Jon H Raphael, Mourad Labib, Jane L Southall, and Robert L Ashford.
• Birmingham City University, Birmingham, UK. ruivduarte@gmail.com
• Pain Physician. 2013 Jan 1;16(1):9-14.

BackgroundHypogonadism is frequently diagnosed based on total testosterone (TT) levels alone. However, 99% of testosterone is bound to the sex hormone-binding globulin (SHBG) with only 1% free testosterone. Alternative assessment methods consist of assay of free testosterone (FT) or bioavailable testosterone (BT) by equilibrium dialysis, calculation of FT and BT through the Vermeulen equations, and calculation of the free androgen index (FAI).ObjectivesThe aim of this study was to investigate the prevalence of hypogonadism in male chronic non-cancer pain patients undertaking long-term intrathecal opioid therapy and the existence of diagnostic discrepancies according to the criteria used.Study DesignProspective observational study.SettingDepartment of Pain Management, Russells Hall Hospital, Dudley, United Kingdom.MethodsTwenty consecutive male patients undertaking long-term intrathecal opioid therapy had the gonadal axis evaluated by assays of luteinising hormone (LH), follicle stimulating hormone (FSH), TT, SHBG and by calculating the FT, BT and FAI.ResultsHypogonadism was present in 17 (85%) of the patients based on TT; 17 (85%) according to FT and BT calculations; and 14 (70%) when calculating FAI. Based on either TT or FT being low or borderline/low, 19 (95%) of the investigated patients were biochemically hypogonadal. Significant differences were observed between diagnosis based on FT and FAI (P < 0.05). No significant differences were observed between diagnosis based on TT and FT (P = 0.40) or TT and FAI (P = 0.20).ConclusionHypogonadism is common in patients undertaking intrathecal opioid therapy for the management of chronic non-malignant pain; however, diagnostic criteria can influence the diagnosis of this side effect. The assessment of the hypothalamic-pituitary-gonadal axis should include evaluation of total serum testosterone, free testosterone, or bioavailable testosterone.

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