Clinical and laboratory characteristics of hypernatraemia in an internal medicine clinic

Hypernatraemia is a frequent electrolyte disorder in hospitalized patients that has been mainly studied in an entire hospital population. The aim of this study was to determine the incidence, clinical characteristics, concomitant electrolyte abnormalities and outcome of hypernatraemia in an internal medicine clinic. Also, we sought to identify differences between patients who were admitted with hypernatraemia and those who developed hypernatraemia during hospitalization.

We prospectively studied patients who either on admission to our internal medicine clinic or during their hospitalization were found to have hypernatraemia (sodium concentration greater than 148 meq/l, 148 mmol/l). One hundred and thirteen patients out of 9158 patients at risk had hypernatraemia (incidence 1.2%). Of those, fifty patients had hypernatraemia on admission, whereas 63 had hospital-acquired hypernatraemia.

Patients who developed hypernatraemia before hospital admission had a much lower mortality rate than patients with hospital-acquired hypernatraemia (28% vs 47.6%, P=0.03), despite the fact that they had a higher peak serum sodium concentration (160.4+/-9.9 vs 154.4+/-2.4 meq/l, P=0.000). Furthermore, they did not differ in either age or the frequency of concomitant electrolyte abnormalities in comparison with patients who developed hypernatraemia during hospitalization. There were two main subgroups of patients with hospital-acquired hypernatraemia. A total of 26 Patients (41%) exhibited a biochemical profile consistent with extracellular volume depletion, whereas 32 patients (51%) with euvolaemia. On the contrary, the majority of patients (82%) who were hypernatraemic on admission had hypovolaemic hypernatraemia. The construction of the receiver operating characteristics (ROC) plots revealed that the urea to creatinine ratio was the best predictor of the extracellular volume status. Indeed, a urea to creatinine value of 57 could differentiate between the groups with euvolaemic or hypovolaemic hypernatraemia with a sensitivity of 96.5% and a specificity of 100%.

The incidence of hypernatraemia in the present study was 1.2% with a high mortality rate mainly in patients with hospital-acquired hypernatraemia. There were two main profiles of hospital-acquired hypernatraemia, one consistent with extracellular volume depletion and another with euvolaemia. On the contrary, the majority of hypernatraemic patients on admission exhibited hypovolaemia. Almost half of our hypernatraemic patients had at least one additional electrolyte disturbance.