The density of human semen and the validation of weight as an indicator of volume: a multicentre study

A multi-centre study was undertaken to: a/ determine the density of human semen, and b/ assess the validity of measuring semen volume either volumetrically or gravimetrically. Semen samples from four clinical categories (azoospermia following vasectomy, azoospermia without vasectomy, oligozoospermia (<20x10(6)/ml) and normozoospermia (>= 20x10(6)/ml)) had similar densities (one-way ANOVA: F(3,180)=1.25, not significant), being close to 1.0 g/ml when taken to one decimal place. Measurement of semen volume was then made with either a graduated pipette or by weighing and assuming a density of 1 g/ml. A comparison of the two methods gave an excellent correlation, with a gradient of 1.0571 and a coefficient of determination (R(2)) of 0.98 (p<0.0001). However, it was noted that the aspiration of the ejaculate in to a graduated pipette underestimated the volume by approximately 0.2 ml, but in an inconsistent manner making the use of a set correction factor inappropriate. The estimation of volume to one decimal place by weighing the collection container before and after ejaculation, assuming a density of 1 g/ml, would seem to be a viable alternative although the density of a small number of samples may deviate from this assumption. Whilst the relatively small underestimation of volume with a pipette is unlikely to have clinical significance, the known reporting of inaccurate results by a laboratory is contrary to the philosophy and key principles of quality management. Reproductive Biology 2010 10 2: 141-153.