ESSENTIALS OF DIAGNOSIS
The two most common etiologies of hyperphosphatemia are decreased kidney clearance from CKD and transcellular shift. Increased dietary intake of phosphates in the setting of advanced CKD can cause hyperphosphatemia. Phosphate-containing laxatives taken as preparation for a GI procedure can cause hyperphosphatemia in patients with impaired kidney function and are less commonly used. Rapid cell breakdown from tumor lysis syndrome, rhabdomyolysis, and massive hemolysis releases intracellular phosphate. Hyperphosphatemia from insulin deficiency can occur in diabetic ketoacidosis (DKA). These patients, however, are typically phosphate depleted and are at risk for developing hypophosphatemia with insulin therapy. Other causes are listed in Table 21–9.
Table Graphic Jump Location Table 21–9.Causes of hyperphosphatemia. ||Download (.pdf) Table 21–9. Causes of hyperphosphatemia.
Massive load of phosphate into the extracellular fluid
Laxatives or enemas containing phosphate
Intravenous phosphate supplement
Rhabdomyolysis (especially if CKD coexists)
Tumor lysis by chemotherapy, particularly lymphoproliferative diseases
Metabolic acidosis (lactic acidosis, ketoacidosis)
Respiratory acidosis (phosphate incorporation into cells is disturbed)
Decreased excretion into urine
Plasma cell myeloma
Hemolysis in vitro
A. Symptoms and Signs
The clinical manifestations are those of the underlying disorder or associated condition. Acute hyperphosphatemia is generally asymptomatic, and symptoms are generally associated with concurrent hypocalcemia.
B. Laboratory Findings
In addition to elevated phosphate, blood chemistry abnormalities are those of the underlying disease.
Treatment is directed at the underlying cause. Acute hyperphosphatemia with symptomatic hypocalcemia and ECG changes (QTc prolongation) can be life-threatening. Intravenous calcium (1–2 g of calcium gluconate over 10–20 minutes) can be given in this situation, though it should be avoided in asymptomatic patients due to the risk of vascular calcification. Hemodialysis may be necessary in patients with impaired kidney function. In chronic hyperphosphatemia, dietary phosphate intake should be decreased and absorption reduced with oral phosphate binders, such as calcium acetate, calcium carbonate, sevelamer, or ferric citrate.
Patients with acute severe hyperphosphatemia require hospitalization for emergent therapy, possibly including dialysis. Concomitant illnesses, such as AKI or cell lysis, may necessitate admission.
J. Phosphate binders in chronic kidney disease: an updated narrative review of recent data. J Nephrol. 2020;33:497.
et al. Current understanding of tumor lysis syndrome. Hematol Oncol. 2019;37:537.