Hyperkalemia, Hyperphosphatemia, Hypocalcemia
Hyperkalemia is often a first sign of TLS, because potassium may start to leave dying cancer cells before they lyse. This electrolyte imbalance can impair normal cardiac function and cause lethal dysrhythmias. The kidneys, overwhelmed by excess potassium in the bloodstream, may be unable to excrete enough potassium to compensate for the hyperkalemia.
Hyperphosphatemia results from the large amount of phosphorus released from malignant cells, especially malignant blood cells.8 The kidneys try to eliminate the excess phosphorus by increasing urine output and reducing the amount of phosphorus reabsorption, but eventually the kidneys reach a point where they can no longer compensate, and phosphorus accumulates in the blood.
As serum phosphate levels increase, phosphate ions (which are negatively charged) combine with calcium ions (positively charged), resulting in decreased serum calcium levels (hypocalcemia). These calcium-phosphate complexes precipitate in soft tissues and the renal tubules, causing tubular obstruction and acute renal failure. Hyperphosphatemia usually develops 24 to 48 hours after the start of chemotherapy.
Purine nucleic acids are also released by lysed cancer cells. Normally, purines are metabolized to hypoxanthine, which is converted to xanthine by the enzyme xanthine oxidase, and then to uric acid, which is excreted by the kidneys. Excess amounts of purine nucleic acids are released quickly into the bloodstream during cancer cell lysis, overwhelming the kidneys' ability to excrete the converted excess amounts of uric acid. This results in hyperuricemia and uric acid crystal formation in the kidneys.
Because of these events, the kidneys are overwhelmed by excess potassium, phosphorus, calcium phosphate precipitates, and uric acid crystals, resulting in acute renal failure. Initially, the kidneys try to compensate for the increased electrolyte and uric acid load by increasing urine output, but they can't maintain normal electrolyte and uric acid levels due to volume depletion and uric acid nephropathy. Hyperuricemia is usually seen 48 to 72 hours after chemotherapy begins.
If a patient is at risk for tumor lysis syndrome, lab work is performed every six hours for the first 24 hours after chemotherapy is started. Lab work consists of a complete blood cell count, serum electrolytes, calcium, phosphorus, creatinine, uric acid, lactate dehydrogenase, and blood urea nitrogen.
After the first 24 hours, lab values are monitored at least every 12 hours for several days and then daily, or as ordered. The severity of the patient's risk helps guide the frequency of lab work.
