In the forensics section of the bat cave (where you enter it the first time), there are four vials of blood. Three are in a drawer on the right and one is on the desk in front of you. To analyze a sample, put it in the centrifuge on the right and hit the spin button (you can do three at once). Once this is done, on the left hand side there is an analysis canister you can raise up. Put a tube inside, lower it, then hit the button to analyze the blood. Repeat for all four tubes.
For the fifth blood sample, use the syringe on the desk to draw a sample from yourself, then stick the syringe in the empty tube to fill it. Follow the rest of the procedure to analyze it and unlock the achievement.