The fallacy of the BUN:creatinine ratio in critically ill patients.
OBJECTIVE
Acute kidney injury (AKI) is common in critically ill patients and is associated with a high mortality rate. Pre-renal azotemia, suggested by a high blood urea nitrogen to serum creatinine (BUN:Cr) ratio (BCR), has traditionally been associated with a better prognosis than other forms of AKI. Whether this pertains to critically ill patients is unknown.


METHODS
We conducted a retrospective observational study of two cohorts of critically ill patients admitted to a single center: a derivation cohort, in which AKI was diagnosed, and a larger validation cohort. We analyzed associations between BCR and clinical outcomes: mortality and renal replacement therapy (RRT).


RESULTS
Patients in the derivation cohort (N = 1010) with BCR >20 were older, predominantly female and white, and more severely ill. A BCR >20 was significantly associated with increased mortality and a lower likelihood of RRT in all patients, patients with AKI and patients at risk for AKI. Patients in the validation cohort (N = 10 228) with a BCR >20 were older, predominantly female and white, and more severely ill. A BCR >20 was associated with increased mortality and a lower likelihood of RRT in all patients and in those at risk for AKI, BUN correlated with age and severity of illness.


CONCLUSIONS
A BCR >20 is associated with increased mortality in critically ill patients. It is also associated with a lower likelihood of RRT, perhaps because of misinterpretation of the BCR. Clinicians should not use a BCR >20 to classify AKI in critically ill patients.
Division of Critical Care Medicine, Department of Medicine, Cooper University Hospital, Camden, NJ, USA.
Jean-Sebastien
JS
Rachoin
Ralph
R
Daher
Charles
C
Moussallem
Barry
B
Milcarek
Krystal
K
Hunter
Christa
C
Schorr
Mariam
M
Abboud
Patricia
P
Henry
Lawrence S
LS
Weisberg
D058186:Acute Kidney Injury / Q000378:metabolism / Q000401:mortality*; D000293:Adolescent; D000328:Adult; D000368:Aged; D001806:Blood Urea Nitrogen; D003404:Creatinine / Q000097:blood*; D016638:Critical Illness / Q000401:mortality*; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D017582:Renal Replacement Therapy / Q000401:mortality*; D012189:Retrospective Studies; D055815:Young Adult
D003404:Creatinine