What is your approach to interpretation of 24 hour urine stone risk studies that persistently demonstrate elevated urinary creatinine excretion despite a reliable patient who denies improper collection?

I would start with a physical examination, looking at muscle mass. Urine creatinine comes from serum creatinine, which in turn comes from muscle mass. Patients with high muscle mass will have high serum and urine creatinine.

If all of the collections are mutually consistent, I presume a high muscle mass or perhaps supplements. I can see the patient and also ask. So I 'screen' for all supplements. As an example, some use protein supplements. I also look for protein catabolic rate (on all competent 24-hour collection plat...

Typically, I don't try to determine the cause, but I use their baseline value to check subsequent collections. It is always difficult to determine the cause for the aberrant value and likewise, difficult to know their true muscle mass, so I simply look for consistency.