When they check the creatinine level, they will also check the pH and SG levels as well.
The creatinine levels and SG levels are checked together in order to arrive at a "diluted" result.

Under US Federal regulations, a "diluted" result is determined when the creatinine level is between 2 - 20 mg/dl and the SG reading is between 1.0010 - 1.0030 on a single aliquot.