Proposed age-stratified reference intervals of FSH derived from normozoospermic men

Objective: To demonstrate that serum follicle-stimulating hormone (FSH) in men rises with age, and to explore FSH reference intervals of age-related partitioning. Methods: Men aged 20-50 years (n=1 190) underwent semen analysis according to World Health Organization (2010) methods. Serum was frozen prior to measurement of FSH by using the Siemens ADVIA Centaur® XP immunoassay system. FSH central 95% intervals after logarithmic transformation based on age were derived from 1 037 normozoospermic men. These were then applied to oligozoospermic and azoospermic men. Men producing azoospermic semen samples were further classified as having non-obstructive azoospermia by clinical diagnostic criteria, including genetic analysis and surgical exploration. Results: Serum FSH in normozoospermic men increased with age (P<0.05), and reference intervals were determined with 10-year brackets: 21-30 years [(1.0-8.2) IU/L], 31-40 years [(1.4-9.5) IU/L], 41-50 years [(1.9-12.0) IU/L]. The proportion of oligozoospermic men with normal FSH concentrations was less than the normozoospermic men, which in turn was lower among azoospermic men (both P<0.01). The azoospermic men were further broken down according to the nature of the azoospermia as either obstructive or non-obstructive azoospermia, and 86.4% (38/44) men with non-obstructive azoospermia had elevated serum FSH concentrations whereas only 6.7% (1/15) men with obstructive azoospermia had high FSH levels, and this was significantly different (P<0.01). Conclusions: FSH concentrations increase in men between 20-50 years, and clinical interpretation of serum FSH results in men must be made by using age-based reference intervals.