What are normal urine creatinine levels?

Q: My niece is under custody of the bureau of prisons. She has been in a half way house for 8 weeks and is being sent back to prison because her urine creatinine is less than 20. They are saying they are not accusing her of drug abuse but it is because of her low levels of creatinine. She exercises regularly, drinks lots of fluids and avoids red meat and smoking. She is not on drugs. Can you shed any light on this topic? We do not understand and are heartbroken. She is 35 years old, 5 feet 6 inches tall and not on any medication. Please tell me about creatinine levels.

A:Urine creatinine, urinary creatinine clearance and serum (blood) creatinine are measured to determine kidney function. The normal range of urine creatinine is 8-18 mmol/d. In kidney dysfunction and hypothyroidism, it can go down.