Some decisions must be left to common sense. The patient that comes to a lab for analyses will have to come back in the case of a rejected specimen. We hope that the former does not return for only a urinalysis prescribed without conviction. As for the serum, urinary substances and elements don't have the same stability. Cells degenerate rapidly while the characteristics of casts will be more easily preserved.
Many crystals seen in urine are absent in the freshly voided specimen.
Specimens that no longer represent the patient at the time of collection and those that could lead to false interpretation should be rejected. It should be remembered that these are an extreme situation. For several reasons, we think that all specimens should be analyzed. The quality of a specimen, that cannot be analyzed rapidly depends on its conservation method. Several centers recommend that specimens be refregerated if they cannot be processed shortly after collection.