What Causes Hyperphosphatemia?

Patient Presentation
A 6-month-old male came to the floor of a regional children’s hospital after being transferred from a local emergency room because of abdominal distention. The local emergency room physicans had contacted a local pediatrician who ordered an enema for the patient. The patient received the enema but had no fecal return. He continued to have abdominal distention and the decision to transfer him was made. Upon arrival at the children’s hospital the patient had bradycardia and a respiratory arrest. After intubation his heart rate increased to normal and he had spontaneous respirations. In the pediatric intensive care unit the pertinent physical exam showed a temperature of 99.8°F, heart rate of 128, respiratory rate of 22, blood pressure of 104/62 with a capillary refill of 3-4 seconds and pale color. He had a grossly distended abdomen without bowel sounds. He had a normal heart rate and sounds. His lungs were clear. He also had intermittent extremity spasms especially of his hands and feet. The pertinent laboratory evaluation at that time showed a glucose of 23 mg/dl, ionized calcium of 1.3 (normal 4.5-5.6 mg/dl), total calcium of 7.4 (normal 9.0-10.5 mg/dl), phosphorous of 28 (normal 3-4.5 mg/dl) and magnesium of 1.9 (normal 1.8-3.0 mg/dl). The differential diagnosis at that time included sepsis with ileus, volvulus, appendicitis with perforation (unlikely due to age), pseudoobstruction, bowel perforation, and metabolic abnormalities. The past medical history that became available later revealed a term infant who stooled around birth but had problems with constipation. A previous rectal biopsy had shown ganglion cells and his neonatal screening test was normal including for cystic fibrosis. He had been treated with oral polyethylene glycol and occasional enemas for constipation. The family history was negative for genetic, metabolic, neurologic or gastrointestinal problems. He was treated for presumed sepsis and hypocalcemia, hypoglycemia, and hyperphosphatemia with aggressive hydration, calcium gluconate, ampicillin, gentamycin and metronidazole, and rectal irrigation.

His clinical course over the next 24 hours, showed having tetany episodes that improved with additional calcium, but eventually his hypocalcemia, hypoglycemia and hyperphoshatemia all resolved. His blood cultures later grew Enterococcus species as a cause of his sepsis. He unfortunately had an ileal perforation that required an ileostomy. During surgery there was normal bowel anatomic alignment and biopsy of various bowel segments showed ganglion cells in all biopsies. Cystic fibrosis and other testing for severe ileus with perforation was being pursued. The tetany and metabolic problems were felt to be caused by the retention of a phosphate-based enema with resulting hyperphosphatemia and hypocalcemia which caused cardiac irritability and cardiopulmonary arrest.

Case Image
Figure 120 – Supine view of the abdomen reveals multiple dilated loops of bowel without evidence of rectal gas. The findings were felt to be compatible with a distal bowel obstruction.

Constipation is a common problem in general pediatrics and its causes are numerous. It can cause acute and recurrent abdominal pain and is a cause of abdominal distention. Patients who are young, whose presentations are other than routine or who had complications should be invested for underlying causes of their constipation. This patient had undergone some evaluations in the past for constipation but because of the presentation of sepsis a more rigorous evaluation was undertaken. The differential diagnoses of the following can be found here: constipation, acute abdominal pain, recurrent abdominal pain, and abdominal distention.

Hyperphosphatemia caused by retention of oral phosphate containing medications and hypertonic sodium phosphate enemas are known causes of hyperphosphatemia. Phosphate-containing medications are used because the hyperosmolarity draws fluid into the intestinal lumen which stimulates peristalsis. Usually the phosphate and fluid are then evacuated. However, the phosphate can be absorbed, particularly if there is lack of bowel integrity, with resulting hyperphosphatemia. With rising concentrations of phosphate, calcium is bound causing hypocalcemia both extracellualrly and intracellularly. Hyperphosphatemia also inhibits Vitamin D hydroxylation and inhibits reabsorption of calcium in the bone. While hypocalcemia is the most common secondary problem due to hyperphosphatemia, hypokalemia, hypomagnesemia and hypoglycemia can also occur. Phosphate toxicity is treated by increasing urinary excretion, phosphate binders (such as aluminum hydroxide) and dialysis.

Hypocalcemia is associated with neuromuscular problems including irritability, poor feeding, emesis, paresthesia, muscle cramps (tetany) seizures, prolongation of the QT interval and cardiac arrhythmias. Chvostek’s sign occurs when tapping on the facial nerve causes facial muscle movement. It is common in hypocalcemia but can also be seen in hypomagnesemia, normal individuals, and patients with migraines or epilepsy. Trousseau’s sign occurs when a blood pressure cuff is inflated around the arm at a pressure greater than systolic pressure for 3 minutes and induces a spasm of the hand and forearm. This also occurs with hypocalcemia. Acidosis and hypoproteinemia tend to protect patients from secondary hypocalcemia problems by increasing the ionized fraction of serum calcium. Hypocalcemia is treated by giving calcium by judicious infusions with either calcium gluconate or calcium chloride. A differential diagnosis of hypercalcemia can be reviewed here.

Learning Point

Phosphate is mainly regulated by parathyroid hormone and dietary/gastrointestinal intake. Therefore hyperphosphatemia occurs primarily because of disregulation to these systems.
The differential diagnosis of hyperphosphatemia includes:

  • Phosphate containing medications and bisphosphonates
  • Renal failure – acute or chronic
  • Hypoparathyroidism
  • Vitamin D toxicity
  • Tumor lysis syndrome
  • Tissue necrosis
  • Rhabdomyolysis
  • Hyperostosis
  • Familial tumoral calcinosis
  • Pseudohyperphosphatemia
  • Acromegaly

Questions for Further Discussion
1. What causes changes in magnesium?
2. What causes changes in potassium?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Fluid and Electrolyte Balance and Minerals.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

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Hebbar K, Fortenberry JD, Parks JS. Severe hypocalcemic tetany and respiratory failure in an infant given oral phosphate soda. Pediatr Emerg Care. 2006 Feb;22(2):118-20.

Domico MB1, Huynh V, Anand SK, Mink R. Severe hyperphosphatemia and hypocalcemic tetany after oral laxative administration in a 3-month-old infant. Pediatrics. 2006 Nov;118(5):e1580-3. Epub 2006 Sep 25.

Stubbs JR, Yu ASL. Overview of the causes and treatment of hypophatemia. UpToDate. (rev. 7/6/2015, cited 6/27/16).

Hasan ZU, Absamara R, Ahmed M. Chvostek’s Sign in Paediatric Practice. Current Pediatric Reviews, 2014:10;194-97.

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa Children’s Hospital