Hypoosmotic swelling test with a medium of distilled water.

The functional competence of the human sperm membrane is assessed by studying the swelling reaction of sperm when suspended in a medium of distilled water (water test). Eighty-seven patients with idiopathic infertility were investigated by the water test and the results were compared with various semen parameters. High correlations with the percentage of b-g type swollen sperm in the water test were observed for sperm concentration (r = .53, p < .05) and percent motility (r = .62, p < .01). The sperm swelling values obtained by the water test correlated well with those obtained by the hypoosmotic swelling test (HOST). Correlation coefficients in b-g and g swelling pattern were 0.89 and 0.71, respectively. The percentage of g-type swelling obtained by the water test was significantly larger than that obtained by the HOST (p < .05), although the two hypoosmotic procedures gave similar percentages of b-g swelling pattern. The percentage of g swelling pattern obtained by the water test correlated well with percent motility (r = .70, p < .001). These findings suggest that the water test is more useful for assessing the integrity of the sperm membrane than the HOST. The relationship between this test and subsequent fertility, as well as to other sperm function tests, needs further investigation.