A client receiving intravenous amphotericin B for treatment of a fungal infection. Which laboratory result is most important for the practical nurse (PN) to report to the healthcare provider? Reference range: Creatinine [0.6 to 1.2 mg/dL (53 to 106 μmol/L)] Hematocrit [42% to 52% (0.42 to 0.52 volume fraction)] Potassium [3.5 to 5.0 mEq/L (3.5 to 5.0 mmol/L)] Platelets [150,000 to 400,000/mm3 (150 to 400 x 10L)]