Hyperphosphatemia may portend poor outcomes in septic acute kidney injury (AKI) patients undergoing continuous renal replacement therapy (CRRT), a new study suggests.

In a post-hoc analysis of their randomized controlled trial on high-volume CRRT (NCT01191905), Su-Young Jung, MD, of Yonsei University in Seoul, South Korea, and colleagues studied all-cause mortality rates within 28 and 90 days of CRRT initiation for 210 septic AKI patients who attended 2 hospital intensive care units in 2011 to 2014. They assessed patients’ levels of sodium, potassium, calcium, and phosphate at 0 and 24 hours after the start of CRRT.

Before CRRT, 126 (60.0%) of patients had at least a single deficiency in electrolytes or minerals and 188 (67.6%) had an excess. Hyperphosphatemia was present in 59.5%. CRRT reduced excesses after 24 hours, whereas hypokalemia and hypophosphatemia developed in more patients.

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Using adjusted models, Dr Jung and colleagues determined that deficiencies were not associated with death, but hyperphosphatemia was. Within 28 days, 89 (71.2%) deaths occurred among patients with hyperphosphatemia (4.5 mg/dL and above) compared with 49 (57.6%) among patients with normal to low phosphate levels below 4.5 mg/dL. The death rate at 90 days also was significantly higher among hyperphosphatemia patients (84% vs 67.1%). Among the 184 survivors of 24-hour CRRT, hyperphosphatemia was associated with a significant 2.2 times and 2.6 times increased risk of death at 28 days and 90 days, respectively.

When serum phosphate was examined as a continuous variable by 1 mg/dL increments, increasing levels again emerged as a significant predictor of death.   

Previous studies, in contrast, have found increased death risks with hypophosphatemia, specifically serum phosphate levels below 1.0 mg/dL. This level of deficiency was rare in the current study.

Higher phosphate levels may be simply a marker of disease severity, the investigators explained. Direct phosphate toxicity is another possibility.

“If phosphate is a biomarker that can reflect disease severity, then more careful attention should be paid to patients with increased phosphate levels,” Dr Jung and colleagues concluded in Medicine.

Among the study’s limitations, they acknowledged a lack of data on magnesium, another potentially relevant mineral.

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1.   1. Jung SY, Kim H, Park S, et al. Electrolyte and mineral disturbances in septic acute kidney injury patients undergoing continuous renal replacement therapy. Medicine. 2016 95;36:e4542. doi: 10.1097/MD.0000000000004542.