Final answer:
The least expected test result for a child with Wilms' tumor would be an elevated HVA with a 24-hour urine collection, as homovanillic acid tests are typically associated with neuroblastoma, not Wilms' tumor.
Step-by-step explanation:
In the context of a child diagnosed with Wilms' tumor, which is a type of kidney cancer often found in children, the least expected test result among the provided options would be 'D) Elevated HVA with 24-hour urine collection'. Homovanillic acid (HVA) tests are commonly associated with neuroblastoma, another type of pediatric malignancy, and not typically with Wilms' tumor. Homovanillic acid (HVA) is a metabolite of the neurotransmitter dopamine, and elevated levels can be indicative of neuroblastoma because it can reflect the tumor's metabolism.
Typically, a complete blood count (CBC) within normal limits (Option A) is not unexpected as Wilms' tumor doesn't necessarily affect blood cell levels unless there is severe disease or the tumor is bleeding. A urinalysis positive for blood (Option B) may occur if the tumor causes bleeding within the kidney, which can spill into the urine. Furthermore, the presence of a mass on the kidney (Option C) is characteristic of Wilms' tumor and would be expected on diagnostic imaging tests like an ultrasound or an MRI.
Other tests may involve checking renal function and for hypercalcemia due to the renal origin of Wilms' tumor. Leukocytosis, or an elevated white blood cell count, might suggest an infection, which isn't directly related to Wilms' tumor unless there is an associated infection.