Final answer:
Creatinine is a metabolic waste product filtered by the kidneys, which are critical in removing waste, regulating fluid balance, and maintaining pH levels.
Step-by-step explanation:
Creatinine is a waste product that is filtered from the blood by the kidneys. These organs serve as the body's natural filtration system, continuously removing various metabolic waste products from the bloodstream.
The kidneys not only filter out substances like creatinine and uric acid but also regulate water balance and maintain the pH of the body's fluids. Creatinine, specifically, is a byproduct of muscle metabolism and is eliminated through urine, which the kidneys produce.