What causes hyperphosphatemia in dogs?

Answer 1

Hyperphosphatemia ---- * Spurious Hyperphosphatemia

1) Hemolysis: Hemolysis or prolonged contact of serum with cells in the blood sample causes movement of phosphate from the red cells into serum and can raise the Pi result.

2) Post-prandial: A mild increase occurs after eating.

3) Monoclonal gammopathy: Hyperphosphatemia can be observed in monoclonal gammopathies, due to binding of phosphate to the monoclonal protein.

* Decreased excretion

1) Decreased GFR: This is the most common cause of hyperphosphatemia. Many animals that are azotemic are also hyperphosphatemic. Acute and severe reduction in GFR, as in acute renal failure or severe hypovolemia, is more likely to result in hyperphosphatemia than is chronic renal failure.

2) Hypoparathyroidism: Phosphate is retained whilst calcium is lost in the urine due to lack of PTH.

3) Acromegaly: Growth hormone promotes retention of phosphate.

4) Hyperthyroidism: Phosphate is increased in up to 21% of hyperthyroid cats.

* Increased absorption

1) Hypervitaminosis D: This produces hyperphosphatemia as well as hypercalcemia.

2) Increased intake: Ingestion of excess phosphate (nutritional hyperparathyroidism) or administration of phosphate containing fluids or compounds. Use of hypertonic phosphate enemas (Fleet) in cats has been recognized to cause extreme hyperphosphatemia through absorption of phosphate. Hypernatremia, hypokalemia, hypocalcemia, and high anion gap metabolic acidosis are additional abnormalities. Affected cats can die. Morbidity and mortality resulting from use of Fleet enemas is increased by prolonged retention of the hypertonic phosphate, mucosal defects enhancing absorption, and pre-existing abnormalities in water and electrolyte balance. This product should be administered to cats with extreme caution if used at all.

* Transcellular shifts

1) Acute tumor lysis syndrome: This results in high phosphate, high potassium, high uric acid and low calcium. Animals often die of acute oliguric renal failure.

2) Severe soft tissue trauma: This can also result in increased phosphate as phosphate is higher intracellularly than extracellularly, e.g. rhabdomyolysis.