Apparatus is provided for testing a biological fluid for presence of a biological particulate. The apparatus includes a tube, a plunger sized and shaped to be inserted into and advanced within the tube, and a filter. The apparatus is configured such that as the plunger is advanced within the tube while the biological fluid is within the tube, the biological fluid in the tube is pushed through the filter, thereby trapping, by the filter, the biological particulate present in the biological fluid. The apparatus is shaped so as to define at least one enclosed cavity containing a biological particulate-presence-testing-facilitation solution configured to test for the presence of the biological particulate trapped by the filter. The enclosed cavity is configured to open while the plunger is inside the tube, so as to release the biological particulate-presence-testing-facilitation solution within the tube. Other embodiments are also described.