The following article provided by the Kern County Regional Criminalistics Laboratory, Toxicology Unit, Bakersfield, CA contains some tips that you have probably overlooked. Enjoy.
Vincent P. Villena (2010) Beating the System: A Study of a Creatinine Assay and Its Efficacy in Authenticating Human Urine Specimens. Journal of Analytical Toxicology, Vol. 34, January/February 2010
