Creatinine comes from your body's everyday use of your muscles -- and also from eating meat. As blood flows through the kidneys, creatinine is excreted out into your urine along with other waste products. Levels of creatinine in the urine taken over 24 hours, together with blood levels of creatinine, can be used to estimate the rate at which your kidneys do their filtering job.
Measuring Urine Creatinine
Determining the level of creatinine in your urine can help your doctor determine whether or not your kidneys are functioning well. The level of creatinine present in the urine can be a good reflection of how well the kidneys are working when combined with other tests. The higher the rate of clearance of waste products like creatinine, the better your kidneys are functioning. Normal rates of filtering are between 90 and 139 milliliters per minute for adult males younger than 40 years, and between 80 and 125 milliliters per minute for adult females younger than 40 years.
What is normal for you may be different than what is normal for someone else. People who eat a lot of red meat will have higher urinary creatinine levels than vegetarians. But for them, this higher level is still normal. Urine creatinine levels also reflect the amount of muscle mass you have. Amputees, for instance, have lower levels. On average, normal creatinine levels are lower in children than adults and lower in women compared to men. Normal urinary creatinine levels also decline with age.