Hyperphosphatemia

Key Features

Essentials of Diagnosis

• Advanced chronic kidney disease (CKD) is the most common cause

• Hyperphosphatemia in the presence of hypercalcemia imposes a high risk of metastatic calcification

General Considerations

• 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 gastrointestinal procedure routinely cause transient hyperphosphatemia, unless the patient has impaired kidney function

• Rapid cell breakdown from tumor lysis syndrome, rhabdomyolysis and massive hemolysis, releases intracellular phosphate

• Hyperphosphatemia from insulin deficiency can occur in diabetic ketoacidosis

• These patients, however, are typically phosphate depleted and are at risk for developing hypophosphatemia with insulin therapy

Etiology

• Massive load of phosphate into the extracellular fluid

  • Exogenous sources

    • Hypervitaminosis D

    • Laxatives or enemas containing phosphate

    • Intravenous phosphate supplement

  • Endogenous sources

    • Rhabdomyolysis (especially if chronic kidney disease 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

  • Chronic kidney disease

  • Acute kidney injury

  • Hypoparathyroidism

  • Pseudohypoparathyroidism

  • Acromegaly

• Pseudohyperphosphatemia

  • Plasma cell myeloma

  • Hyperbilirubinemia

  • Hypertriglyceridemia

  • Hemolysis in vitro

Clinical Findings

• 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

Diagnosis

• In addition to elevated phosphate, blood chemistry abnormalities are those of the underlying disease

Treatment

• Treatment is directed at the underlying cause

• Intravenous calcium

  • Can be given in life-threatening cases of acute hyperphosphatemia with symptomatic hypocalcemia and ECG changes (QTc prolongation)

  • Should be avoided in asymptomatic patients due to the risk of vascular calcification

• Hemodialysis may be necessary in patients with impaired kidney function

• Oral phosphate binders

  • Used in chronic hyperphosphatemia to decrease dietary phosphate intake and reduce absorption

  • Examples include

    • Calcium acetate

    • Calcium carbonate

    • Sevelamer

    • Ferric citrate

Outcome

When to Admit

• Patients with acute severe hyperphosphatemia require hospitalization for emergent therapy, possibly including dialysis

• Concomitant illnesses, such as acute kidney injury or cell lysis, may necessitate admission

References