Hyperphosphatemia
Hyperphosphatemia is a serum phosphate level above 4.5 mg/dL (1.45 mmol/L), most often from reduced renal excretion in advanced chronic kidney disease or from acute cellular lysis in tumor lysis syndrome or rhabdomyolysis. Management sequences correction of the underlying cause and kidney function with dietary phosphate restriction, phosphate binders, and dialysis, while chronic elevation drives CKD-mineral and bone disorder, secondary hyperparathyroidism, and vascular calcification.
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What this article covers
- Overview
Hyperphosphatemia is defined as a serum phosphate level greater than 4.5 mg/dL (1.45 mmol/L).
- Epidemiology
Hyperphosphatemia is essentially a universal complication of advanced CKD: serum phosphorus stays normal until eGFR drops below 30 mL/min/1.73 m2 (stage G4-G5), the point at which compensatory…
- Risk factors
CKD stage G4-G5 or end-stage kidney disease, the dominant risk factor, once eGFR falls below 30 mL/min/1.73 m2.
- Pathophysiology
Reduced renal phosphate excretion from decreased GFR is the dominant mechanism: rising FGF-23 (from stage G3a) and PTH increase phosphate excretion and maintain normal phosphorus as GFR falls, until…
- Clinical features
Most patients are asymptomatic, with hyperphosphatemia detected incidentally on a metabolic panel, particularly with mild to moderate chronic elevation.
- Differential diagnosis
Tumor lysis syndrome: rapid cellular breakdown after (or independent of) cytotoxic therapy; distinguished by concurrent hyperuricemia, hyperkalemia, hypocalcemia, and AKI.
- Diagnosis
Hyperphosphatemia is confirmed by a serum phosphate level greater than 4.5 mg/dL (1.45 mmol/L); a hemolyzed or improperly handled sample can falsely elevate the result, so an unexpected value should be repeated before acting on it.
- Management
First, determine whether kidney function is adequate and whether the elevation is acute or chronic.
- Complications
Secondary and, if unaddressed, tertiary hyperparathyroidism, from sustained PTH stimulation by chronic hyperphosphatemia and hypocalcemia.
- Prognosis
Elevated phosphorus, PTH, and FGF-23 are associated with increased cardiovascular events and mortality in CKD/end-stage kidney disease; observational data suggest a mortality benefit from lowering…
- Prevention
In CKD stages G3a to G5, lower elevated phosphorus toward the normal range through dietary modification with or without phosphate binders, per KDIGO guidelines, rather than waiting for overt hyperphosphatemia.
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Related articles
- Chronic kidney disease mineral and bone disorders
Chronic kidney disease-mineral and bone disorder (CKD-MBD) is the syndrome of disturbed calcium, phosphorus, PTH, vitamin D, and FGF-23 homeostasis, abnormal bone mineralization (renal osteodystrophy), and vascular calcification that develops as kidney function declines. Management centers on serial phosphorus/calcium/PTH monitoring, dietary phosphorus restriction plus phosphate binders (noncalcium-based preferred) to normalize phosphorus, avoiding hypercalcemia and unnecessary calcitriol before dialysis, and calcimimetics or activated vitamin D for uncontrolled secondary hyperparathyroidism on dialysis, reserving parathyroidectomy for tertiary disease.
- Acute kidney injury
Acute kidney injury is a sudden rise in serum creatinine or fall in urine output from prerenal, intrinsic, or postrenal causes, defined and staged by KDIGO criteria. Management targets the underlying cause, corrects volume and electrolyte derangements, and escalates to renal replacement therapy for refractory hyperkalemia, acidosis, volume overload, or uremia.
- Tumor lysis syndrome (TLS)
Tumor lysis syndrome is a metabolic oncologic emergency in which massive tumor cell breakdown, spontaneous or chemotherapy-induced, releases potassium, phosphate, and nucleic acids into the blood, producing hyperuricemia, hyperkalemia, hyperphosphatemia, and secondary hypocalcemia that can precipitate acute kidney injury, arrhythmia, seizure, and death. Risk-stratified prophylaxis with hydration plus allopurinol or rasburicase before chemotherapy, and aggressive correction of electrolytes with renal replacement therapy when needed, are the cornerstones of management.
- Rhabdomyolysis
Rhabdomyolysis is necrosis of skeletal muscle with release of myoglobin, creatine kinase, and intracellular electrolytes into the circulation, diagnosed by a serum creatine kinase at least five times the upper limit of normal (typically over 1500 U/L) with a urine dipstick positive for blood but no red cells on microscopy; treatment is aggressive isotonic intravenous fluid to a urine output of 200 to 300 mL/h and correction of hyperkalemia, with acute kidney injury from pigment nephropathy the dominant complication.
- Hypocalcemia
Hypocalcemia is a low serum calcium concentration, most often from insufficient parathyroid hormone action (postsurgical or autoimmune hypoparathyroidism, hypomagnesemia, or PTH resistance) or from vitamin D deficiency and chronic kidney disease. Severe or symptomatic disease requires urgent intravenous calcium, while chronic disease is managed with oral calcium, vitamin D repletion, and calcitriol when PTH is absent or the kidney cannot activate vitamin D.
- Hypoparathyroidism
Hypoparathyroidism is PTH deficiency causing hypocalcemia and hyperphosphatemia, most often from inadvertent parathyroid injury during anterior neck surgery. First-line treatment is oral calcium plus calcitriol titrated to a low-normal serum calcium, with recombinant PTH reserved for inadequate control.
- Calciphylaxis
Calciphylaxis, also called calcemic uremic arteriopathy, is a form of vascular calcification that produces extensive calcification of the skin, muscles, and subcutaneous tissue, leading to ischemic ulceration and necrosis, most often in patients with end-stage renal disease. There is no single diagnostic test; management centers on normalizing serum calcium and phosphate, increasing the intensity of dialysis, non-calcium phosphate binders and calcimimetic therapy, and aggressive pain control and wound care.