Hyperphosphataemia after bowel preparation with oral sodium phosphate

Dr. Mishra et al. [1] presented two patients with renal impairment who developed severe symptomatic hyperphosphataemia and hypocalcaemia after bowel preparation with oral sodium phosphate. They postulated that a significant increase in serum phosphate can occur after a single dose of sodium phosphate when the patient’s serum creatinine is over 2.0 mg/dL.

We recently published a prospective study of the biochemical effects of sodium phosphate preparation in 100 patients undergoing colonoscopy [2]. We support the conclusion that hyperphosphataemia can occur in patients with renal impairment. None of our patients had significant renal impairment, the highest creatinine level recorded being 1.64 mg/dL (145 mmol/L). We found that the serum phosphate was elevated with any degree of renal impairment, and all the patients with a serum creatinine of over 1.22 mg/dL (108 mmol/L) had a serum phosphate above the normal range, with a correlation between creatinine and serum phosphate found across the range. Elevated serum phosphate also correlated independently with increasing age. In addition, we found that hyperphosphataemia was more likely in patients taking angiotensin-converting enzyme (ACE) inhibitors, AT₂-receptor antagonists, or diuretics.

We believe that any degree of renal impairment can lead to the development of hyperphosphataemia after colonoscopy preparation with oral sodium phosphate and that the risk is increased by older age and by the medications mentioned above.

Competing interests: None

References

• 1 Mishra R, Kaufman D, Mattern J III, Dutta S K. Severe hyperphosphatemia and hypocalcemia caused by using oral sodium phosphate in end-stage renal disease.  Endoscopy. 2005;  37 1259
• 2 Ainley E J, Winwood P J, Begley J P. Measurement of serum electrolytes and phosphate after sodium phosphate colonoscopy bowel preparation: an evaluation.  Dig Dis Sci. 2005;  50 1319-1323