The Effects of Pre-Existing Hyponatremia and Subsequent-Developing Acute Kidney Injury on In-Hospital Mortality: A Retrospective Cohort Study.
OBJECTIVE
Both hyponatremia and acute kidney injury (AKI) are common and harmful in hospitalized patients. However, their combined effects on patient mortality have been little studied.


METHODS
We retrospectively enrolled 19191 adult patients who were admitted for 1 year. Pre-existing hyponatremia was defined as a serum sodium level < 135 mmol/L on the first measurement of their admission. AKI was defined as a rise in serum creatinine by ≥ 26.5 μmol/L or ≥ 1.5 times of the baseline value of creatinine during the hospital stay.


RESULTS
The prevalence of pre-existing hyponatremia was 8.2%. During a median 6.0 days of hospital stay, the incidence rates of AKI and in-hospital patient mortality were 5.1% and 0.9%, respectively. Pre-existing hyponatremia independently predicted AKI development and in-hospital mortality (adjusted hazard ratio [HR] 1.300, P = 0.004; HR 2.481, P = 0.002, respectively). Pre-existing hyponatremia and subsequent development of AKI increased in-hospital mortality by 85 times, compared to the patients with normonatremia and no AKI. In subgroup analysis, the AKI group showed higher rates of de novo hypernatremia than the non-AKI group during the admission. De novo hypernatremia, which might be associated with over-correction of hyponatremia, increased in-hospital mortality (HR 3.297, P <0.001), and patients with AKI showed significantly higher rates of de novo hypernatremia than patients without AKI (16.2% vs. 1.4%, P < 0.001, respectively).


CONCLUSIONS
Pre-existing hyponatremia may be associated with the development of AKI in hospitalized patients, and both hyponatremia and hospital-acquired AKI could have a detrimental effect on short term patient mortality, which might be related to the inappropriate correction of hyponatremia in AKI patients.
Department of Internal Medicine, Seoul National University Postgraduate School, Seoul, Korea.|Department of Internal Medicine, Eulji General Hospital, Seoul, Korea.
Sung Woo
SW
Lee
Department of Internal Medicine, Seoul National University Postgraduate School, Seoul, Korea.|Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
Seon Ha
SH
Baek
Department of Internal Medicine, Korea University Guro Hospital, Seoul, Korea.
Shin Young
SY
Ahn
Department of Internal Medicine, Seoul National University Postgraduate School, Seoul, Korea.|Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
Ki Young
KY
Na
Department of Internal Medicine, Seoul National University Postgraduate School, Seoul, Korea.|Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
Dong-Wan
DW
Chae
Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
Ho Jun
HJ
Chin
Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
Sejoong
S
Kim
D058186:Acute Kidney Injury / Q000209:etiology* / Q000401:mortality*; D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D007010:Hyponatremia / Q000150:complications* / Q000401:mortality* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D056910:Republic of Korea / Q000453:epidemiology; D012189:Retrospective Studies; D012307:Risk Factors