Incidence and aetiology of renal phosphate loss in patients with hypophosphatemia in the intensive care unit

Hypophosphatemia is a common finding in patients in the intensive care unit (ICU). Its cause is often poorly understood. The aim of this study was to understand the incidence of renal phosphate loss in ICU-related hypophosphatemia, and to examine the role of phosphaturic hormones in its etiology. Plasma phosphate levels were measured on day 1, 3, 5 and 7 in 290 consecutive patients admitted to the ICU. Renal phosphate handling and phosphaturic hormones were studied in a subset of patients with phosphate levels < 0.6 mmol/L. Renal phosphate loss was defined as a TmP/gfr < 0.6 mmol/L. Hypophosphatemia developed in 24 % of all patients. This mainly occurred within the first 3 days of stay and in patients with serum creatinine levels < 150 mu mol/L. Renal phosphate loss was present in 80 % of patients who developed hypophosphatemia, and was not related to serum levels of parathyroid hormone (PTH), PTH-related protein (PTH-rp), fibroblast growth factor 23 (FGF-23), or calcitonin. Hypophosphatemia in the ICU is commonly associated with renal phosphate loss. It mainly occurs within the first 3 days of admission, in particular in patients with preserved renal function. Renal phosphate loss is not explained by elevated PTH, PTH-rp, FGF-23 or calcitonin levels.