Azoospermia and normal follicle-stimulating hormone (FSH) levels – role of α-glucosidase as discriminator between patients with or without obstruction

Objective: Although α-glucosidase determination is included in the WHO Handbook for Semen Analysis, its value in the infertility workup is controversial. We reinvestigated its diagnostic power to distinguish between obstructive (OA) and non-obstructive azoospermia (NOA).

Methods: 164 healthy volunteers with normal sperm concentration formed the control group. The group with proven OA consisted of 86 patients diagnosed with vasectomy (n=55) or congenital bilateral absence of vas deferens (CBAVD, n=31). 79 patients with azoospermia and normal FSH levels (≤7 U/l) but no apparent clinical reasons for azoospermia were subdivided according to an α-glucosidase threshold derived from the control group.

Results: The 2.5-percentile (16 mU/ejaculate) of α-glucosidase in the control group was chosen as the cut-off to categorise the study groups. 33 patients had α-glucosidase levels below (suspected OA) and 46 above this threshold (susp. NOA). The susp. OA group was indistinguishable from the group with proven OA. In contrast, those with susp. NOA differed significantly from the proven OA group in semen volume, fructose and α-glucosidase (higher) and testicular volume and age (lower). No differences in hormone levels were found except that the control group had higher LH and lower FSH. All patients of the susp. OA group with available histology had elongated spermatids in their biopsy (16/16) while in the susp. NOA group several patients with spermatogenic arrest were identified (6/16; 10 had elongated spermatids) giving a specificity of 100% (pos. predictive value: 100%) and sensitivity of 62% (neg. predictive value: 38%) for an α-glucosidase of 16 mU/ejac.

Conclusion: The α-glucosidase level of 16 mU/ejac., slightly below the WHO cut-off level of 20 mU/ejac. derived from proven fathers, provides a discriminator useful when counselling patients with azoospermia and normal FSH about the likelihood of finding sperm in a biopsy (specificity 100%). However, the sensitivity of 62% is rather poor. Fructose and zinc do not improve diagnosis.