Why is creatinine measured in a 24 hour urine collection?

Tell kidney function. Single urine specimens can be tested for creatinine. But daily urine output and urinary concentration varies hence a 24 hr urine collection. Normal creatinine output for an adult should be >1gm/24 hours. Also getting blood creatinine provides optimal way to accurately determine creatine clearance which in turn is a most accurate way to measure kidney function.