Bias to routine semen analysis by uncontrolled changes in laboratory environment--detection by long-term sampling of monthly means for quality control.

To detect systematic bias in the results of routine semen analysis over time, monthly means of semen parameters determined by the recommended WHO methods were computed. The analysis was based on a total sample size of 1784 ejaculates and included 18 months of observation. In addition to slight changes of morphology estimates caused by a change of laboratory staff, a major bias in the measurement of sperm motility could be detected. This observation triggered a search for changes in protocols not previously given the required attention. It revealed that the newly introduced use of polypropylene syringes with a mounted needle for accurate measurement of seminal volume impaired sperm motility. More detailed investigation by computerized sperm motion analysis in 10 semen samples treated simultaneously in different ways revealed that predominantly it was the needle which caused the drop in proportion of motile sperm (glass cylinder: 50.3 +/- 4.1% vs. syringe + needle: 26.6 +/- 5.3%; mean +/- SEM) and not the contact with the plastic material alone (syringe alone: 43.4 +/- 4.8%). Other motion parameters such as curvilinear velocity (36.0 +/- 1.6 microns/sec), linearity (78.5 +/- 8.4%) and lateral head displacement (3.8 +/- 0.9) were not influenced by the different methods of handling. The results indicate that long-term sampling of monthly means may serve as part of a quality control scheme in semen analysis.