Updated: Jan 31, 2008
Phosphorus is the sixth most abundant element in the human body. It is critical for bone mineralization, cellular structure, genetic coding, and energy metabolism. Many organic and inorganic forms exist. The adult body contains approximately 1000 g of phosphorus, of which 80-90% is in bone. An additional 10-14% is intracellular and the remaining 1% is extracellular.
The phosphorus in plasma is 12-17% protein bound. Free serum compounds represent much less than 1% of the total body phosphorus content. This fraction also varies with shifts between the intracellular and extracellular compartments. Thus, serum phosphorus levels may not reflect accurately the total body phosphorus content.
Levels are expressed in terms of serum phosphorus mass (mg/dL). One mg/dL of phosphorus is equal to 0.32 mmol of phosphate. The normal adult range is 2.5-4.5 mg/dL (0.81-1.45 mmol/L). Levels are 50% higher in infants and 30% higher in children because of growth hormone effects.
Hyperphosphatemia is considered significant when levels are greater than 5 mg/dL in adults or 7 mg/dL in children or adolescents.
Phosphorus homeostasis normally is maintained through several mechanisms. Gastrointestinal (GI) absorption must be matched by renal excretion, and cellular release is balanced by uptake in other tissues. Hormonal control is provided mainly by parathyroid hormone.
Hyperphosphatemia occurs when the phosphorus load (from GI absorption, exogenous administration, or cellular release) exceeds renal excretion and tissue uptake.
GI absorption
Phosphorus is present in nearly all foods, and GI absorption of dietary forms is very efficient. With low dietary intake, 80-90% is absorbed. When intake is greater than 10 mg/kg daily, 70% is absorbed. Normal daily dietary intake varies from 800-1500 mg.
Absorption occurs mainly in the jejunum, although some absorption occurs throughout the intestinal tract. A small amount of phosphorus is secreted into the GI tract.
Serum phosphorus levels
Serum phosphorus levels rise after a large meal. Antacids decrease absorption because calcium, aluminum, and magnesium bind phosphorus into insoluble complexes. Aluminum is the most efficient binder found in antacids.
Renal excretion and reabsorption
To maintain homeostasis, renal phosphorus excretion normally matches the amount of daily GI absorption. Excretion occurs in the proximal tubule and is largely dependent on the filtered phosphorus load. As the filtered load increases, a higher fraction of excreted phosphorus is reabsorbed.
Reabsorption is also dependent on concurrent sodium transport. However, while sodium that is not reabsorbed at the proximal tubule may be reabsorbed distally, this is not true for phosphorus. Proximal diuretics, which decrease sodium reabsorption, also increase phosphorus excretion. The usual load excreted is 5-15% of the filtered load or 600-800 mg/d in the normal net steady state. This amount may increase markedly in hyperphosphatemia. Marked hyperphosphatemia is unusual in chronic renal insufficiency unless the glomerular filtration rate (GFR) is less than 25 mL/min. Secretion plays an insignificant role in renal phosphorus excretion.
Hyperphosphatemia occurs most often in patients with renal insufficiency. Most patients with acute or chronic renal failure have hyperphosphatemia in some degree. To avoid hyperphosphatemia, patients with end-stage renal disease and a GFR <30 must restrict their intake of dietary phosphorus. If dietary restriction alone does not reduce serum phosphate levels into the normal range, oral phosphate binders should be added to reduce absorption.
Sequelae of hyperphosphatemia
Hyperphosphatemia causes hypocalcemia by precipitating calcium, decreasing vitamin D production, and interfering with parathyroid hormone-mediated bone resorption. Severe life-threatening hypocalcemia may result. Signs and symptoms of acute hyperphosphatemia are due to the effects of hypocalcemia.
Prolonged hyperphosphatemia promotes metastatic calcification, an abnormal deposition of calcium phosphate in previously healthy connective tissues such as cardiac valves and in solid organs such as muscles. The calcium-phosphate product predicts the risk of metastatic calcification.
Excess free serum phosphorus is taken up into vascular smooth muscle via a sodium-phosphate cotransporter. The increased cellular phosphate activates a gene, cbfa-1, that promotes calcium deposition in the vascular cell, making smooth muscle cells engage in osteogenesis. Vascular walls become calcified and arteriosclerotic, leading to increased systolic blood pressure, widened pulse pressure, and subsequent left ventricular hypertrophy.
Hyperphosphatemia is an independent risk factor contributing to the increased incidence of aortic and mitral stenosis and other cardiovascular disease among dialysis-dependent patients. A peripheral form known as calcific uremic arteriolopathy (calciphylaxis) can induce necrotic ulceration and gangrene in affected extremities.
Hyperphosphatemia-induced resistance to parathyroid hormone contributes to secondary hyperparathyroidism and renal osteodystrophy.
Patients with end-stage renal disease make up the bulk of patients with hyperphosphatemia. Approximately 250,000 persons are affected.
Prolonged hyperphosphatemia is an independent risk factor for cardiovascular disease in patients with renal failure. Patients with chronic phosphate levels above 6.5 have an 18-39% higher mortality compared with patients with renal failure with near-normal serum phosphate levels.
Although women have physiologic elevation of serum phosphate levels after menopause, this has no known clinical significance.
The nervous and cardiovascular systems are most commonly affected.
Phosphorus balance between intracellular and extracellular compartments and between bone and other tissues may be influenced by many factors. The most common cause of hyperphosphatemia is decreased renal excretion due to renal insufficiency from any cause. All marked elevations of phosphorus involve significant addition of phosphorus to the extracellular compartment, usually with some impairment of renal function.
Hypercalcemia
Hypermagnesemia
Hypocalcemia
Pseudohyperphosphatemia is most commonly due to paraproteinemia from the following:
Waldenström macroglobulinemia
Multiple myeloma
Monoclonal gammopathy of unknown significance
Most symptoms and sequelae are due to secondary hypocalcemia. Initial care is aimed at management and correction of the hypocalcemia and its sequelae. Endpoints of therapy include resolution of symptoms and a serum calcium level within the low reference range.
Oral phosphate binders are used to decrease the highly efficient GI absorption of phosphorus. Calcium salts are widely used but may produce hypercalcemia. Aluminum salts are effective binders but may induce aluminum toxicity. Newer compounds containing iron or bile acid sequestrants are replacing calcium and aluminum binders.
Proximal diuretics are phosphuretic to the same extent they are natriuretic. Acetazolamide is particularly efficient in promoting renal phosphate excretion.
These agents decrease GI phosphate absorption.
The polymer forms ionic and hydrogen bonds with phosphates and bile acids to promote fecal excretion. Lowers serum phosphate to near normal levels in hemodialysis patients as effectively as calcium acetate without inducing hypercalcemia or increased aluminum levels. Maintains stable iPTH levels and increases alkaline phosphatase levels compared to calcium acetate.
2.4-4.8 g PO divided tid with meals
Not established
May decrease absorption of oral medications causing a decrease in levels of antiarrhythmics and antiepileptics
Documented hypersensitivity; bowel obstruction, hypophosphatemia
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Caution in patients with dysphagia, altered GI motility or GI tract surgery; measure serum phosphate and calcium frequently to adjust dose to keep serum phosphate <6 mg/dL
Combines with dietary phosphate to form calcium acetate, which is then excreted in feces.
4-8 g PO divided tid with meals
Not established
May increase effect of quinidine; may decrease effects of tetracyclines, atenolol, salicylates, iron salts, and fluoroquinolones; IV administration antagonizes effects of verapamil; large intakes of dietary fiber may decrease calcium absorption and levels
Documented hypersensitivity; hypercalcemia or hypercalcuria may occur when therapeutic amounts are given
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Monitor serum calcium and phosphate frequently; adjust dose to keep serum phosphate less than 6 mg/dL; avoid use of over-the-counter antacids
Noncalcium, nonaluminum phosphate binder indicated for reduction of high phosphorus levels in patients with end-stage renal disease. Directly binds dietary phosphorus in upper GI tract, thereby inhibiting phosphorus absorption.
Initial: 250-500 mg PO tid pc (chewable tabs); adjust dose q2-3wk to target serum phosphorus level
Maintenance: 500-1000 mg PO tid pc
Not established
Drugs known to interact with antacids (eg, alendronate, amprenavir, ciprofloxacin, itraconazole, tetracycline, thyroid hormones) should not be administered within 2 h
Documented hypersensitivity; bowel obstruction; hypophosphatemia
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Deposited into developing bone, including growth plate (long-term effects unknown); common adverse effects typically diminish over time but include headache, abdominal pain, nausea, diarrhea, constipation, and vomiting; in clinical trials, dialysis graft occlusion occurred more frequently than with placebo; caution with GI motility diseases (eg, Crohn disease, ulcerative colitis) or recent GI surgery
These agents are used to treat symptomatic hypocalcemia resulting from hyperphosphatemia by replacing calcium.
IV preparation used in treatment of symptomatic hypocalcemia, particularly for treatment of tetany. In absence of symptoms, hypocalcemia may be treated with oral supplements rather than IV infusions. Calcium gluconate 10% solution contains 100 mg/mL = 0.45 mEq elemental calcium/mL.
2 g (20 mL) IV over 10-30 min initially, followed by maintenance dose of 0.5-2 mg/kg/h
Neonates: 200-800 mg/kg/d IV continuous infusion or divided qid
Infants and children: 100-200 mg/kg IV over 10 min initially, followed by maintenance dose of 200-500 mg/kg/d IV continuous infusion or divided qid
May decrease effects of tetracyclines, atenolol, salicylates, iron salts, and fluoroquinolones; antagonizes effects of verapamil; large intakes of dietary fiber may decrease calcium absorption and levels
Renal calculi; hypercalcemia; hypophosphatemia; renal or cardiac disease; digitalis toxicity
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Caution in digitalized patients, respiratory failure, acidosis, or severe hyperphosphatemia
IV preparation used in treatment of severe symptomatic hypocalcemia. Do not confuse calcium chloride with calcium gluconate; calcium chloride contains approximately 3 times as much elemental calcium per unit weight as does calcium gluconate. In absence of symptoms, hypocalcemia may be treated with oral supplements rather than IV infusions. Calcium chloride 10% solution contains 100 mg/mL = 1.4 mEq/mL.
500-1000 mg slow IV q6h
10-20 mg/kg/dose slow IV q4-6h prn
With digoxin may cause arrhythmias; with thiazides may induce hypercalcemia; may antagonize effects of calcium channel blockers, atenolol, and sodium polystyrene sulfonate
Ventricular fibrillation not associated with hyperkalemia; digitalis toxicity; hypercalcemia; renal insufficiency; cardiac disease
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Administer slowly (not to exceed 0.5-1 mL/min) to avoid extravasation; hypercalcemia may occur in renal failure
These agents increase renal excretion of phosphate.
Increases renal excretion of phosphorus.
250-375 mg PO/IV qd in am
5 mg/kg PO/IV qd in am
Can decrease therapeutic levels of lithium and alter excretion of drugs (amphetamines, quinidine, phenobarbital, salicylates) by alkalinizing urine
Documented hypersensitivity; hepatic disease; severe renal disease; adrenocortical insufficiency; severe pulmonary obstruction
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Patients with impaired hepatic function may go into coma; may cause substantial increase in blood glucose in some diabetic patients
Sutherland SM, Hong DK, Balagtas J, Gutierrez K, Dvorak CC, Sarwal M. Liposomal amphotericin B associated with severe hyperphosphatemia. Pediatr Infect Dis J. Jan 2008;27(1):77-9. [Medline].
Berner YN, Shike M. Consequences of phosphate imbalance. Annu Rev Nutr. 1988;8:121-48. [Medline].
Bleyer AJ, Burke SK, Dillon M, et al. A comparison of the calcium-free phosphate binder sevelamer hydrochloride with calcium acetate in the treatment of hyperphosphatemia in hemodialysis patients. Am J Kidney Dis. Apr 1999;33(4):694-701. [Medline].
Block GA, Port FK. Re-evaluation of risks associated with hyperphosphatemia and hyperparathyroidism in dialysis patients: recommendations for a change in management. Am J Kidney Dis. Jun 2000;35(6):1226-37. [Medline].
Card RT, Brain MC. The "anemia" of childhood: evidence for a physiologic response to hyperphosphatemia. N Engl J Med. Feb 22 1973;288(8):388-92. [Medline].
Chan J, Gill J Jr, eds. Kidney Electrolyte Disorders. Churchill Livingston; 1990:247-60, 460.
Chertow GM, Burke SK, Raggi P. Sevelamer attenuates the progression of coronary and aortic calcification in hemodialysis patients. Kidney Int. Jul 2002;62(1):245-52. [Medline].
Fauci A, Braunwald E, et al, eds. Harrison's Principles of Internal Medicine. New York: McGraw-Hill; 1998:1510, 2217-8, 2243, 2245, 2262.
Larner AJ. Pseudohyperphosphatemia. Clin Biochem. Aug 1995;28(4):391-3. [Medline].
Liu YL, Lin HH, Yu CC, Kuo HL, Yang YF, Chou CY. A comparison of sevelamer hydrochloride with calcium acetate on biomarkers of bone turnover in hemodialysis patients. Ren Fail. 2006;28(8):701-7. [Medline].
London GM, Pannier B, Marchais SJ, Guerin AP. Calcification of the aortic valve in the dialyzed patient. J Am Soc Nephrol. Apr 2000;11(4):778-83. [Medline].
Medical Economics Staff. Physicians' Desk Reference. 54th ed. Medical Economics Co; 2000:811-2, 3339-40.
Rostand SG. Coronary heart disease in chronic renal insufficiency: some management considerations. J Am Soc Nephrol. Oct 2000;11(10):1948-56. [Medline].
Rutecki G, Whittier F. Decision points in hypocalcemia: is emergent therapy required?. J Crit Illn. 1998;13(2):84-90.
Rutecki G, Whittier F. Life-threatening phosphate imbalance: when to suspect, how to treat. J Crit Illn. 1997;12(11):699-704.
Schrier R, ed. Renal and Electrolyte Disorders. 4th ed. Boston: Little Brown & Co; 1992:287-315.
Schrier R, Gottschalk C, eds. Diseases of the Kidney. 6th ed. Boston: Little Brown & Co; 1997:2490-4.
Slatopolsky E. New developments in hyperphosphatemia management. J Am Soc Nephrol. Sep 2003;14(9 Suppl 4):S297-9. [Medline].
Sutters M, Gaboury CL, Bennett WM. Severe hyperphosphatemia and hypocalcemia: a dilemma in patient management. J Am Soc Nephrol. Oct 1996;7(10):2056-61. [Medline].
Thatte L, Oster JR, Singer I. Review of the literature: severe hyperphosphatemia. Am J Med Sci. Oct 1995;310(4):167-74. [Medline].
Wang AY, Woo J, Sea MM, et al. Hyperphosphatemia in Chinese peritoneal dialysis patients with and without residual kidney function: what are the implications?. Am J Kidney Dis. Apr 2004;43(4):712-20. [Medline].
phosphorus homeostasis, high phosphorus level, hyperphosphatemia, renal insufficiency, acute renal failure, chronic renal failure, end-stage renal disease, hypocalcemia, calcific uremic arteriolopathy, calciphylaxis, managing hyperphosphatemia and chronic kidney disease
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