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.