Normal levels of phosphorus are between 2.5 to 4.5mg/dL (0.81-1.45 mmol/L). Hyperphosphatemia is characterized by phosphate levels above 4.5mg/dL (>1.46mmol/L).
Shift from intracellular – >extracellular:
Acute metabolic or respiratory acidosis
Excessive oral or rectal use of an oral phosphate-saline laxative or enema
Excessive parenteral administration of phosphate
Vitamin D intoxication
Renal failure (acute or chronic)
Causes of false elevations of measured phosphate (pseudohyperphosphatemia):
Blood sample taken from line containing heparin or alteplase
High concentrations of paraproteins
In vitro hemolysis
SIGNS & SYMPTOMS:
Most patients are asymptomatic and the symptoms, when present, are usually related to other abnormalities that may be associated (in hypocalcemic patients: muscle cramps, tetany, numbness and tingling; in uremic patients, fatigue, shortness of breath, nausea, sleep disorders).
Acute hyperphosphatemia is often a result of intracellular -> extracellular shift (tumor lysis syndrome, rhabdomyolisis, among other causes). In patients with normal kidney function, the treatment should be focused on promoting phosphaturia with the administration of normal saline as well as acetazolamide and sodium bicarbonate if needed. Patients with acute hyperphosphatemia and bad kidney function may benefit from insulin and glucose or dialysis (peritoneal dialysis may be better in such cases).
Chronic hyperphosphatemia, which occurs often in patients with chronic kidney disease, should be treated with low phosphate diet to a maximum dietary intake of 900mg/day (avoid dairy products, sodas, processed foods) and phosphate binders (e.g. Sevelamer 800-1600mg TID, lanthanum carbonate 1500-4500mg daily, calcium acetate or calcium carbonate). Phosphate binders are indicated for all patients with CKD and eGFR <60mL/min/1.73m2 with hyperphosphatemia that does not respond to oral restrictions alone. The ideal phosphate levels in CKD patients is below 3.5mg/dL (1.13mmol/L). For patients with CKD refractory hyperphosphatemia despite diet and binders, daily or prolonged dialysis, calcimimetics or parathyroidectomy may be necessary.
SOURCES & FURTHER READING:
- Hruska KA et al. Hyperphosphatemia of chronic kidney disease. Kidney International. Volume 74, Issue 2, 2 July 2008, Pages 148-157.
- Malberti F. Hyperphosphataemia: treatment options. Drugs. 2013 May;73(7):673-88.
- Lederer E. Hyperphosphatemia. Medscape. Updated: Nov 17, 2016.
- Coladonato JA. Control of Hyperphosphatemia among Patients with ESRD. JASN November 1, 2005 vol. 16 no. 11 suppl 2 S107-S114.