Aim: To determine the predictive value of the hypo-osmotic swelling (HOS) test to identify viable, non-motile sperm. Methods: Semen samples from 20 men with severe asthenozoospermia underwent traditional seminal analysis, eosin-nigrosin (EN) staining and the HOS test. A further EN stain was then performed on a HOS pre-treated aliquot and a total of 2000 further sperm examined. Results: The median sperm density was 5.1 million/mL (IQR 4.3~13.1) and the median motility was 3.0 % (IQR 0~7). Seven samples showed complete asthenozoospermia. Initial EN staining showed 59 % viability (range 48~69) despite the poor standard parameters and 47 % (range 33~61) in the complete asthenozoospermia subgroup. The HOS test showed 49.9 % reacted overall (range 40~59) and 41.7 % (range 22~61) in the complete asthenozoospermia subgroup. The combined HOS/EN stain showed the positive predictive value of the HOS test to identify viable sperm was 84.2 % overall and 79.7 % in the complete asthenozoospermia subgroup. Conclusion: The HOS test can effectively predict sperm viability in patients with severe and complete asthenozoospermia.

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