(See also Overview of Disorders of Phosphate Concentration Overview of Disorders of Phosphate Concentration Phosphorus is one of the most abundant elements in the human body. Most phosphorus in the body is complexed with oxygen as phosphate. About 85% of the about 500 to 700 g of phosphate in the... read more .)
Etiology of Hyperphosphatemia
The usual cause of hyperphosphatemia is
Decrease in renal excretion of phosphate
Advanced renal insufficiency (glomerular filtration rate [GFR] < 30 mL/minute) reduces excretion sufficiently to increase serum phosphate. Defects in renal excretion of phosphate in the absence of chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more also occur in pseudohypoparathyroidism Pseudohypoparathyroidism Hypocalcemia is a total serum calcium concentration < 8.8 mg/dL (< 2.20 mmol/L) in the presence of normal plasma protein concentrations or a serum ionized calcium concentration < 4... read more , hypoparathyroidism Hypoparathyroidism Hypocalcemia is a total serum calcium concentration < 8.8 mg/dL (< 2.20 mmol/L) in the presence of normal plasma protein concentrations or a serum ionized calcium concentration < 4... read more , and parathyroid suppression (as from hypercalcemia Hypercalcemia Hypercalcemia is a total serum calcium concentration > 10.4 mg/dL (> 2.60 mmol/L) or ionized serum calcium > 5.2 mg/dL (> 1.30 mmol/L). Principal causes include hyperparathyroidism... read more due to vitamin A or vitamin D excess or granulomatous disease).
Hyperphosphatemia occasionally results from a transcellular shift of phosphate into the extracellular space that is so large that the renal excretory capacity is overwhelmed. This transcellular shift occurs most frequently in
Overwhelming systemic infections
Hyperphosphatemia can also occur with excessive oral phosphate administration and occasionally with overzealous use of enemas containing phosphate.
Hyperphosphatemia can be spurious in cases of hyperproteinemia (eg, in multiple myeloma Multiple Myeloma Multiple myeloma is a cancer of plasma cells that produce monoclonal immunoglobulin and invade and destroy adjacent bone tissue. Common manifestations include lytic lesions in bones that cause... read more or macroglobulinemia Macroglobulinemia Macroglobulinemia is a malignant plasma cell disorder in which B cells produce excessive amounts of IgM M-proteins. Manifestations may include hyperviscosity, bleeding, recurrent infections... read more ), dyslipidemia Dyslipidemia Dyslipidemia is elevation of plasma cholesterol, triglycerides (TGs), or both, or a low high-density lipoprotein cholesterol (HDL-C) level that contributes to the development of atherosclerosis... read more , hemolysis, or hyperbilirubinemia.
Pathophysiology of Hyperphosphatemia
Hyperphosphatemia plays a critical role in the development of secondary hyperparathyroidism Hyperparathyroidism Hypercalcemia is a total serum calcium concentration > 10.4 mg/dL (> 2.60 mmol/L) or ionized serum calcium > 5.2 mg/dL (> 1.30 mmol/L). Principal causes include hyperparathyroidism... read more and renal osteodystrophy in patients with advanced chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more as well as in patients on dialysis.
Hyperphosphatemia can lead to calcium precipitation into soft tissues, especially when the serum calcium × phosphate product is chronically > 55 mg2/dL2 (4.4 mmol2/L2) in patients with chronic kidney disease.
Soft-tissue calcification in the skin is one cause of excessive pruritis in patients with end-stage renal disease who are on chronic dialysis. Vascular calcification also occurs in patients on dialysis who have a chronically elevated calcium × phosphate product; this vascular calcification is a major risk factor for cardiovascular morbidity, including stroke Overview of Stroke Strokes are a heterogeneous group of disorders involving sudden, focal interruption of cerebral blood flow that causes neurologic deficit. Strokes can be Ischemic (80%), typically resulting... read more , myocardial infarction Acute Myocardial Infarction (MI) Acute myocardial infarction is myocardial necrosis resulting from acute obstruction of a coronary artery. Symptoms include chest discomfort with or without dyspnea, nausea, and/or diaphoresis... read more , and claudication.
Symptoms and Signs of Hyperphosphatemia
Most patients with hyperphosphatemia are asymptomatic, although symptoms of hypocalcemia Symptoms and Signs Hypocalcemia is a total serum calcium concentration < 8.8 mg/dL (< 2.20 mmol/L) in the presence of normal plasma protein concentrations or a serum ionized calcium concentration < 4... read more , including tetany, can occur when concomitant hypocalcemia is present.
Soft-tissue calcifications are common among patients with chronic kidney disease; they manifest as easily palpable, hard, subcutaneous nodules often with overlying scratches. Imaging studies frequently show vascular calcifications lining major arteries.
Diagnosis of Hyperphosphatemia
Phosphate concentration > 4.5 mg/dL (> 1.46 mmol/L)
Hyperphosphatemia is diagnosed by phosphate concentration.
When the etiology is not obvious (eg, rhabdomyolysis, tumor lysis syndrome, renal failure, overingestion of phosphate-containing laxatives), additional evaluation is warranted to exclude hypoparathyroidism Hypoparathyroidism Hypoparathyroidism is a deficiency of parathyroid hormone often caused by an autoimmune disorder or by iatrogenic damage or removal of the glands during thyroidectomy or parathyroidectomy. Symptoms... read more or pseudohypoparathyroidism Pseudohypoparathyroidism Hypocalcemia is a total serum calcium concentration < 8.8 mg/dL (< 2.20 mmol/L) in the presence of normal plasma protein concentrations or a serum ionized calcium concentration < 4... read more , which is end-organ resistance to parathyroid hormone (PTH).
False elevation of serum phosphate also should be excluded by measuring serum protein, lipid, and bilirubin concentrations.
Treatment of Hyperphosphatemia
Sometimes saline diuresis or hemodialysis
The mainstay of treatment in patients with advanced chronic kidney disease is reduction of phosphate intake, which is usually accomplished with avoidance of foods containing high amounts of phosphate and with use of phosphate-binding medications taken with meals. Although quite effective, aluminum-containing antacids should not be used as phosphate binding agents in patients with end-stage renal disease because of the possibility of aluminum-related dementia and osteomalacia.
Calcium carbonate and calcium acetate are frequently used as phosphate binders. But their use requires close monitoring because of the possibility of excessive calcium × phosphate product causing vascular calcification in patient on dialysis who are taking calcium-containing binders.
A phosphate-binding resin without calcium, sevelamer, is widely used in patients on dialysis. It is given in doses of 800 to 2400 mg orally 3 times a day with meals. Lanthanum carbonate is another phosphate binder that lacks calcium and is used in patients on dialysis. It is given in doses of 500 to 1000 mg orally 3 times a day with meals.
Sucroferric oxyhydroxide combines elemental iron with phosphate binding because many patients on dialysis need both. It is given in doses of 500 mg orally 3 times a day with meals.
Hemodialysis Hemodialysis In hemodialysis, a patient’s blood is pumped into a dialyzer containing 2 fluid compartments configured as bundles of hollow fiber capillary tubes or as parallel, sandwiched sheets of semipermeable... read more does remove some phosphate, but not enough to allow most patients with end-stage renal disease to avoid significant hyperphosphatemia without dietary interventions.
Saline diuresis can be used to enhance phosphate elimination in cases of acute hyperphosphatemia in patients with intact kidney function. Hemodialysis can lower phosphate levels in cases of severe acute hyperphosphatemia.
The usual cause of hyperphosphatemia is advanced renal insufficiency; hypoparathyroidism and pseudohypoparathyroidism are less common causes.
Most patients are asymptomatic, but those who also are hypocalcemic may have tetany.
Treat by restricting dietary phosphate and sometimes with phosphate binders.
Saline diuresis or hemodialysis may be needed.
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