Your questions pertain to accurate urinary sampling.
Additional information follows.
OSHA has received several questions concerning overhydration and its effects on urinary sample results. In Appendix F of the cadmium standard, OSHA specified a number of sample collection and handling procedures for enhancing the accuracy of blood and urine samples taken as part of the cadmium biological monitoring program. OSHA now believes this prehydration procedure may lead to overhydration in some instances, thereby lowering CRTU levels. This third sample should be collected without first drinking a glass of water. If screening tests indicate that the CRTU levels is still too low, then the renal function of the employee should be evaluated medically to rule out other possible etiologies that may account for these effects.