Final answer:
The nurse should report elevated creatinine levels to the provider.
Step-by-step explanation:
The nurse should report to the provider an elevated creatinine levels in the laboratory report of the preschooler with Wilm's tumor. Elevated creatinine levels indicate impaired renal function, which can be a result of the tumor affecting the kidneys. This information is important for the provider to assess the child's overall health and plan appropriate treatment.