Measurement of viscosity of human semen with a rotational viscometer

The viscosity of 130 human seminal plasma samples was studied with a rotational viscometer instead of by the traditional subjective rating method. The average seminal viscosity one hour after ejaculation was 9.35 +/- 0.99 centipoise (cps), which was statistically identical to that in the third hour (8.63 +/- 0.77 cps). Seminal viscosity showed a significant negative correlation with the percentage of motile sperm (p < 0.05); however, no significant correlation between seminal viscosity and sperm concentration could be found (r = -0.15, p = 0.098). The seminal viscosity of the oligoasthenospermic group was significantly higher than that of the normospermic group (p < 0.01); there was also a trend towards higher viscosity in the semen of asthenospermia and oligospermia when compared with the normospermic group. It is concluded that seminal viscosity may be higher in cases of poor-quality semen; however, sperm motility and concentration are not the sole determinants of viscosity. Determining the seminal viscosity with this rapid, objective and quantitative method is valuable in identifying and treating the subgroup of infertile men with viscid semen.