Choosing among different technical variations of Percoll centrifugation for sperm selection.

We compared the efficiency of different methodological variations of the centrifugation through discontinuous Percoll gradients (PC) to improve semen samples in the laboratory. Five different combinations of the number, volume and density of PC layers were assayed in 14 semen samples presenting various qualities. Each specimen was divided into five aliquots and processed simultaneously. The percentage of spermatozoa showing optimal movement (VAP > 30 microns s-1 and STR > 80%) after PC selection when the number of gradients was reduced to three or two (PC-3: 43.3%, PC-2: 41.3%) and when the volume of layers was diminished to 0.5 ml (mPC-3: 44.2%, and mPC-2: 48.1%), was higher than in classical columns with four gradients of 1 ml (PC-4: 26.3%). The absolute recovery of optimal sperm was better with PC-2, mPC-2 and mPC-3. In samples showing low concentration or motility of spermatozoa, mPC-2 was the most effective technique. PC-2 and mPC-2 showed a tendency to eliminate more red blood cells contaminating the samples. Straight line velocity and straightness were similarly improved by all the methods. We conclude that the technique of PC centrifugation with only two gradients is simpler and more effective for sperm selection and in cases of poor samples can be used with low-volume layers.