The practical nurse (PN) is caring for an older client who is receiving chemotherapy for lung cancer. Which finding is the highest priority for the PN to report to the charge nurse? Reference ranges: Blood urea nitrogen (BUN): [Adult: 10 to 20 mg/dL or 3.6 to 7.1 mmol/L] Platelets: [150,000 to 400,000/mm3 or 150 to 400 x 10^9/L]

A. Platelet count 135,000/mm³ or 135 x 10⁹/L: This mild thrombocytopenia is a common effect of chemotherapy and does not require urgent intervention unless the count drops below 100,000/mm³ or active bleeding occurs. B. Blood urea nitrogen 75 mg/dL or 12.9 mmol/L: A BUN level this high indicates severe renal impairment or dehydration, both of which are critical in a chemotherapy patient. Renal dysfunction can result from nephrotoxic effects of chemotherapeutic drugs and must be reported immediately to prevent further kidney damage. C. Decreased deep tendon reflexes: While this may suggest electrolyte imbalance or peripheral neuropathy, it is not immediately life-threatening and can be monitored until further evaluation. D. Periodic nausea and vomiting: These are expected side effects of chemotherapy and, though uncomfortable, do not represent an acute or life-threatening condition compared to severe renal dysfunction reflected by the elevated BUN.