In urine sediment preparation, what is the purpose of centrifugation?

• A. Sterilize sample
• B. Concentrate sediment and allow microscopic evaluation
• C. Dissolve crystals
• D. Remove all bacteria

Answer: (B)

The main idea is to concentrate the material in urine so you can see it under a microscope. Urine is mostly liquid, and the formed elements you want to examine—like red and white blood cells, crystals, casts, bacteria, and debris—are present in small numbers. Centrifugation uses centrifugal force to push these dense particles into a pellet at the bottom of the tube, allowing you to remove most of the liquid and resuspend the concentrated sediment for slide preparation. This makes microscopic evaluation much more reliable than looking at raw urine. It’s not a sterilization step, it doesn’t dissolve crystals, and it doesn’t remove all bacteria; it simply concentrates what’s present so you can detect it more easily.