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

Abstract

Background: Hypophosphatemia is a common finding in patients in the intensive care unit (ICU). Its cause is often poorly understood.

Purpose: 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.

Methods: 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.

Main results: 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 μmol/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.

Conclusion: 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.