Urine output in diagnosing acute kidney injury and predicting mortality

• Main Authors: Md Ralib, Azrina, Mat Nor, Mohd Basri
• Format: Conference or Workshop Item
• Language: English
• Published: 2015
• Subjects: R Medicine (General)
• Online Access: http://irep.iium.edu.my/43430/1/MSA_NGAL_AZRINA.pdf; http://irep.iium.edu.my/43430/; http://www.msa.asm.org.my/pview_eposters1.asp

Background: Urine output is the oldest biomarker of AKI. Clinically it can be the first indication of kidney dysfunction, especially in critical care settings where hourly urine outputs are routinely measured. It has been shown that the ideal urine output threshold for prediction of mortality or dialysis was 0.3 ml/kg/h for moving block of 6 hours. Objectives: We aim to assess this threshold in mortality prediction in our ICU population. Methods: This was a secondary analysis of a single centre, prospective observational study. Admission of less than 48 hours, post-elective surgery and ICU readmission were excluded. A moving average urine output over 6 hours over body weight was calculated for the first 48th hour post ICU admission. AKIuo was defined if urine output less than 0.5 ml/kg/h, and UO0.3 less than 0.3 ml/kg/h. Results: A total of 143 patients were recruited, of these 87 (61%) had AKIuo, and 52 (36%) had UO0.3. The AUC of AKIuo in predicting mortality was 0.62 (0.51 to 0.72), and UO0.3 was 0.66 (0.55 to 0.77). There were lower survival in patients with AKIuo and UO0.3 compared to those without (p=0.01, and 0.001, respectively). However, after adjusting for covariates (age and SOFA score without renal score), only UO0.3 but not AKIuo independently predicted mortality (HR 2.44 (1.15 to 5.18)). AKUuo assessed over 6 hours or longer independently predicted mortality, whereas UO0.3 assessed over 2 hours or longer predicted mortality. Conclusions: A threshold of 6 hourly urine output of 0.3 ml/kg/h but not 0.5 ml/kg/h was independently predictive of mortality. Duration of urine output assessed as low as 2 hours can be used when utilisng the stricker definiton, whereas at 6 hours is needed using the standard criteria. This support previous finding of a more stricker urine output definition in acute kidney injury.