Final answer:
The substance poured off after centrifuging a urine sample is called the supernatant. It contains mostly fluid processed by the kidneys to efficiently remove wastes and is used for further diagnostic analysis.
Step-by-step explanation:
The term used for the substance that should be poured off after a urine sample is centrifuged is known as the supernatant. When a urine sample is centrifuged, the heavier particles settle at the bottom forming a layer called the sediment, while the clear liquid above is the supernatant.
This supernatant part of the sample may be decanted for further analysis, and it predominantly consists of a fluid with a variable composition that has been processed by the kidneys to safely and efficiently remove wastes from the body. The examination of the supernatant can provide important diagnostic information, just as the sediment may also be analyzed for the presence of cells, bacteria, crystals, and other substances that help diagnose various diseases.