TMP/GFR AND IONIZED CALCIUM IN THE MANAGEMENT OF SEVERE HYPOPHOSPHATEMIA

Severe hypophosphataemia (serum phosphate concentration less than 0-32 mmol/L) due to phosphate depletion can lead to a number of serious complications if left uncorrected including respiratory failure, cardiac failure and haemolytic anaemia.1-3 These effects are secondary to intracellular depletion of adenosine triphosphate (ATP).4 The management of phosphate depletion has been controversial as intravenous phosphate in high doses can cause widespread metastatic calcification and severe hypocalcaemia. In addition, patients in renal failure are likely to develop hyperkalaemia. In view of these problems, it is recommended that low doses of intravenous phosphate are given and that serum calcium, potassium and phosphate concentrations are measured regularly during the course of management.5 We report the results of ionized calcium assays during the treatment of three severely hypophosphataemic patients and TmP/GFR ratios prior to the commencement of therapy. The TmP/GFR ratio (a measure of the renal tubular reabsorption of phosphate) was used to help elucidate the source of phosphate loss.