A nurse is caring for a client who has a fungal infection and has a new prescription for gentamicin. Which laboratory finding should the nurse report to the provider before administering the medication?

A. Gentamicin is an aminoglycoside antibiotic with a very high risk of nephrotoxicity, as it is primarily excreted unchanged by the kidneys. An increased serum creatinine indicates impaired glomerular filtration and a high risk for drug accumulation and further renal damage. The nurse must report this finding to prevent potential permanent kidney injury and to allow for appropriate dosage adjustments based on clearance. B. While an increased serum sodium level, or hypernatremia, requires clinical attention, it is not a specific contraindication or a primary adverse effect associated with gentamicin therapy. Gentamicin does not directly interfere with sodium regulation or the endocrine mechanisms of water balance. The nurse should prioritize findings that suggest organ-specific toxicity related to the drug's known safety profile, such as renal dysfunction. C. Decreased serum potassium can occur with various medications, but it is not a classic hallmark of aminoglycoside toxicity or a reason to withhold an initial dose of gentamicin. Hypokalemia would be more concerning if the patient were taking diuretics or digoxin. In the context of gentamicin, the most critical electrolyte disturbances are usually secondary to the renal tubular damage indicated by rising creatinine. D. Increased blood glucose levels are typically associated with diabetes mellitus or corticosteroid use rather than aminoglycoside administration. Gentamicin does not affect insulin secretion, peripheral glucose uptake, or hepatic gluconeogenesis in a clinically significant manner. Therefore, while hyperglycemia is an important metabolic finding, it does not represent an immediate safety risk specifically tied to the administration of this antibiotic.