Adverse renal and metabolic effects associated with oral sodium phosphate bowel preparation

Abstract

Colorectal cancer can be prevented by the removal of adenomatous polyps during screening colonoscopy, but adequate bowel preparation is required. Oral sodium phosphate (OSP), an effective bowel purgative, is available over the counter and requires a substantially lower volume than polyethylene glycol-based preparative agents. Accumulating reports implicate OSP in electrolyte disturbances as well as acute kidney injury (AKI) in a syndrome termed phosphate nephropathy (a form of nephrocalcinosis). Despite published case reports and case series, the actual incidence, risk factors, and natural history of phosphate nephropathy remain largely undefined. Several recent observational studies have provided new information on these important issues while supporting a link between OSP and acute phosphate nephropathy as well as the development of chronic kidney disease in elderly patients, many of whom had a normal serum creatinine at the time of OSP ingestion. This review summarizes current knowledge about the renal complications of OSP, risk factors for its development, and the pathophysiology of acute and chronic kidney damage in nephrocalcinosis.

Figure 1.

Clinical course observed in a 74-yr-old who received 90 ml of oral sodium phosphate solution before colonoscopy. (36) Reproduced by permission, © Georg Thieme Verlag KG.

Figure 2.

Renal pathology in nephrocalcinosis. (A) Hematoxylin and eosin-stained biopsy from a patient with phosphate nephropathy. Note the evidence of acute tubular injury with simplified epithelial cell brush borders and necrotic luminal cell debris. (B) von Kossa stain of the same biopsy specimen reveals abundant intraluminal calcium crystals. (C) Hematoxylin and eosin-stained glomerulus from a patient with acute kidney injury and inflammatory bowel disease. (D) On polarized light, the calcium oxalate crystals from the same section are positively birefringent. (E) Hematoxylin and eosin-stained section from a patient with advanced malignancy with bony metastases and hypercalcemia. Note the thickening of tubular basement membranes. (F) von Kossa stain from the same biopsy reveals typical findings in metastatic calcification with punctate and linear tubular basement calcium phosphate crystals.