The spectrum of hypophosphatemia in internal medicine: lessons from a Greek population study

Hypophosphatemia, a common but often overlooked electrolyte disorder in hospitalized patients, lacks routine monitoring. This study aimed to assess the incidence, causes and associated biochemical and clinical features, as well as concurrent electrolyte and acid-base disturbances and mortality in patients with hypophosphatemia in an internal medicine ward.

We prospectively included adult patients who either presented with or developed hypophosphatemia (serum phosphate levels < 2.5 mg/dL or 0.81 mmol/L) during hospitalization.

Among 4,095 patients, 4.3% (n = 176) had or developed hypophosphatemia. Of those, 126 patients (71.6%) had hypophosphatemia on admission, while 50 patients (28.4%) developed hypophosphatemia during hospitalization. All but one patient exhibited mild (72.2%) or moderate (27.3%) hypophosphatemia with serum phosphate levels between 2 and 2.5 mg/dL (0.65-0.81 mmol/L) and 1-2 mg/dL (0.32-0.65 mmol/L), respectively. The most common potential causes of phosphate depletion were respiratory alkalosis, malnutrition, drugs, e.g. diuretics and corticosteroids, diabetes mellitus and secondary hyperparathyroidism, with most patients (75.6%) exhibiting more than one likely causes. 64.8% of patients had at least one concomitant electrolyte disorder, the most common being hypocalcemia (40.9%), hyponatremia (38.6%), hypomagnesemia (23.9%) and hypokalemia (22.7%). 77% of patients exhibited pure or mixed acid-base disorders, mainly respiratory alkalosis (48.3%). Mortality was markedly higher in hypophosphatemic patients compared to the overall hospitalized population (15.9% vs. 4.26%). Furthermore, 8.1% of discharged patients had died within a month. Patients who developed hypophosphatemia during hospitalization were older, with higher incidence of hyponatremia and mortality rate (16% versus 5.6%). They also had higher parathyroid hormone and lower vitamin D levels, compared with those with hypophosphatemia on admission.

Hypophosphatemia in internal medicine patients is often multifactorial and may signal greater illness severity. The high prevalence of associated electrolyte and acid-base disturbances suggests shared underlying mechanisms.