Aim: The aim of this study was to determine the most common causes of hypophosphataemia (⩽0.5 mmol/l) in a hospital population in order to identify patient groups at risk of developing the condition.

Methods: The study was conducted at Tygerberg Hospital, a tertiary care centre in the Western Cape, South Africa. All patients identified with a phosphate level ⩽0.5 mmol/l during an 18-month period were included in the study. Medical records of these patients were reviewed.

Results: Of all the requests received for serum phosphate determination by the laboratory, 2% (861 out of 45 394 requests) were ⩽0.5 mmol/l. Thirty per cent (30%; n = 189) of the patients in the study population died during their hospital stay. Most (45%; n = 278) of the patients with low phosphate levels occurred in an intensive care setting, whereas 10% (n = 63) were most likely due to refeeding, and 6% (n = 35) had neoplastic disease. Sepsis was implicated as a contributing factor in 26% (n = 162).

Conclusion: Severe hypophosphataemia is associated with a very high mortality (30%, n = 189). Patients with a high risk of developing hypophosphataemia include those in an intensive care unit (ICU), patients suffering from neoplastic diseases, possible refeeding syndrome and septic patients. Regular phosphate determination is recommended in these patients to facilitate early diagnosis of hypophosphataemia.