not be corrected unless the patient’s serum potassium falls in a critically low range (less than mEq/L), significant muscular weakness develops, or if hypokalemia is associated with EKG changes Hypocalcemia should remain uncorrected as well, unless clinical signs or symptoms develop Supplemental calcium may increase the risk of formation of calcium phosphate precipitates in the kidney Renal tubular dysfunction is common in oncology patients Patients may waste electrolytes such as sodium, potassium, calcium, magnesium, and phosphorus through their kidneys as a result of specific treatment exposures or prior renal injury Antifungal agents such as amphotericin and ambisome cause potassium wasting, which may have clinical significance Calcineurin inhibitors, such as tacrolimus or cyclosporine, which may be used after stem cell transplantation, can cause significant magnesium wasting Patients with hypomagnesemia are more likely to experience seizures when on calcineurin inhibitors so the magnesium should be kept more than 1.8 mEq/L in these patients In addition, patients with tumors of the CNS may renally waste sodium so monitoring of serum sodium is crucial, especially in the postoperative period Patients receiving drugs that cause salt wasting are often prescribed oral electrolyte replacement However, inability to tolerate oral medications or nonadherence may allow electrolyte abnormalities to develop Most of these derangements are clinically asymptomatic with the notable exceptions of hypocalcemia, which can cause tetany or cardiac arrhythmias and hyponatremia resulting in refractory seizures For the most part, management and replacement strategies for these electrolyte abnormalities not differ from children who not have cancer (see Chapter 100 Renal and Electrolyte Emergencies ) However, when replacing calcium in pediatric oncology patients, the clinician should remember that hypomagnesemia, a common side effect of cancer therapies, could complicate efforts to address hypocalcemia Elevated blood sugar can be a transient side effect of corticosteroids as well as asparaginase therapy Asparaginase affects the body’s ability to make many proteins, including insulin In ALL treatment, steroids and asparaginase may be used together and hyperglycemia may result Treatment need not include insulin if dietary measures alone are sufficient to control the serum blood sugar If blood glucose is greater than 250 mg/dL or is significant enough to cause glycosuria or ketonuria, treatment with small doses of insulin may be considered However, the approach to insulin use in this setting should be conservative so as to limit the risks of hypoglycemia Diabetic ketoacidosis is rare in this situation High serum calcium levels are observed commonly in the setting of adult malignancy but are rare in children with cancer Hypercalcemia is usually related to the tumor destroying bone or to ectopic production of parathyroid hormone by the