Are you saying that in the 6405N SAP 5-50 gc/ms test they don't even check creatinine levels unless it makes it to the gc/ms portion
The GC/MS is used only to confirm the presence of drugs and two types of adulterants: glutaraldehyde and pyridine. Creatinine is checked with a seperate colorimetric dipstick before the drug assay is performed. In some cases, labs would use a drug assay with integrated panels for creatinine, SG, pH, etc.

Color is not an accurate means to determine creatinine and SG levels. Even samples with a nice yellow color to them can still fall below the acceptable limits for creatinine and SG, and thus being ruled "too-dilute".