Urine Output of 300 mL Over 24 Hours Corresponds to Stage 3 Acute Kidney Injury
A urine output of 300 mL over 24 hours meets the KDIGO criteria for Stage 3 AKI, as this represents severe oliguria (<0.3 mL/kg/h for ≥24 hours) in most adult patients. 1
KDIGO Staging Based on Urine Output Criteria
The KDIGO classification system stages AKI severity using both serum creatinine and urine output thresholds, with urine output criteria defined as follows:
- Stage 1: Urine output <0.5 mL/kg/h for 6-12 hours 1
- Stage 2: Urine output <0.5 mL/kg/h for ≥12 hours 1
- Stage 3: Urine output <0.3 mL/kg/h for ≥24 hours OR anuria for ≥12 hours 1
Calculating the Stage for 300 mL/24 Hours
To determine the stage, you must calculate the hourly urine output per kilogram of body weight:
- For a 70 kg patient: 300 mL ÷ 24 hours = 12.5 mL/h ÷ 70 kg = 0.18 mL/kg/h
- For a 60 kg patient: 300 mL ÷ 24 hours = 12.5 mL/h ÷ 60 kg = 0.21 mL/kg/h
- For an 80 kg patient: 300 mL ÷ 24 hours = 12.5 mL/h ÷ 80 kg = 0.16 mL/kg/h
In all typical adult body weights (50-100 kg), 300 mL over 24 hours yields a rate well below the Stage 3 threshold of 0.3 mL/kg/h sustained for 24 hours. 1
Clinical Significance of Stage 3 AKI
Stage 3 AKI carries the highest mortality risk among all AKI stages, with patients requiring renal replacement therapy experiencing approximately four-fold higher in-hospital mortality compared to lower stages. 2 Progressive advancement through KDIGO stages correlates with incrementally higher mortality risk. 2
Even when diagnosed by urine output criteria alone (without meeting serum creatinine thresholds), Stage 3 AKI is associated with significantly worse outcomes. 3 Oliguria lasting more than 12 hours (Stage 2 or 3) has major diagnostic implications and is independently associated with 90-day mortality regardless of serum creatinine elevations. 3
Important Caveats and Pitfalls
Body Weight Dependency
The actual KDIGO stage depends on the patient's body weight—you must know the patient's weight to definitively assign a stage. 1 However, for any adult weighing more than approximately 40 kg, 300 mL/24 hours will meet Stage 3 criteria.
Unreliable Populations
Urine output criteria should NOT be used as the primary diagnostic tool in certain populations:
Cirrhotic patients with ascites: These patients are frequently oliguric with avid sodium retention despite maintaining relatively normal GFR, making urine output unreliable. 1, 4 Focus exclusively on serum creatinine changes in this population. 1, 4
Patients receiving diuretics: Diuretic therapy confounds urine output interpretation and makes the criteria less reliable. 1, 4
Measurement Method Matters
The method used to calculate urine output significantly affects AKI diagnosis and staging. 5 Using consecutive hourly readings (each hour must meet the threshold) versus mean hourly output can more than double the reported incidence of AKI. 5 The KDIGO criteria do not specify which method to use, creating potential inconsistency. 5
Integration with Serum Creatinine Criteria
Remember that AKI staging uses the worst criterion met—either serum creatinine OR urine output. 1 A patient may simultaneously meet:
- Stage 3 by urine output (<0.3 mL/kg/h for ≥24 hours)
- Stage 1 by serum creatinine (1.5-1.9× baseline)
In this case, the patient is classified as Stage 3 AKI because that is the more severe criterion. 1
Immediate Management Implications
When Stage 3 AKI is identified by severe oliguria:
- Discontinue all nephrotoxic medications immediately (NSAIDs, ACE inhibitors, ARBs, aminoglycosides) 2
- Assess volume status and provide fluid resuscitation if hypovolemic 2
- Rule out urinary obstruction with renal ultrasound 2
- Monitor serum creatinine and electrolytes every 4-6 hours 2
- Obtain urgent nephrology consultation for Stage 2 or 3 AKI 6
- Evaluate for indications for renal replacement therapy (severe oliguria unresponsive to fluid resuscitation, severe metabolic acidosis, uremic complications) 2