Annexin columns The annexin columns allow for sperm selection based on their capacity to discriminate between live spermatozoids and apoptotic spermatozoids. Sperm selection methods like the density gradients and the swim-up technique make it possible to select the spermatozoids with greater mobility. The annexin columns, however, respond to the needs to select between mobile spermatozoids, and those that are alive. In the laboratory the semen sample is left to incubate in an annexin solution conjugated with an iron micro particle. The apoptotic spermatozoids will remain attached to the iron particle and, when passing the sample over a column under the effect of a magnet, these will remain trapped in the column, while the live spermatozoids will no longer be attached.