Acute Kidney Injury (AKI)

Definition : 

Acute Kidney Injury (AKI) is an abrupt decline in kidney function, leading to retention of waste products, electrolyte imbalance, and fluid dysregulation. It is classified based on etiology and severity.  

Types of AKI by Etiology 

Pre-Renal AKI   

Cause: Decreased renal perfusion without intrinsic kidney damage.  

Examples:  

• Hypovolemia (dehydration, hemorrhage). 
• Hypotension/shock (sepsis, cardiogenic shock) 
• Heart failure, liver failure 

Documentation Tip:   Specify underlying cause (e.g., “AKI due to hypovolemia from GI bleed”).  

Intrinsic (Intra-Renal) AKI  

Cause: Direct damage to kidney tissue.  

Examples:  

• Acute Tubular Necrosis (ATN\) – ischemia or nephrotoxins 
• Acute Interstitial Nephritis (AIN) – drug-induced, autoimmune 
• Glomerulonephritis 

Documentation Tip: If ATN or AIN is suspected, document specifically (e.g., “AKI secondary to ATN from contrast exposure”). 

Post-Renal AKI  

Cause: Obstruction of urine flow.  

Examples:  

• Ureteral obstruction (stones, tumors) 
• Bladder outlet obstruction (BPH, neurogenic bladder) 
• Documentation Tip: State the obstructive cause (e.g., “AKI due to bilateral ureteral obstruction from stones”). 

Diagnostic Criteria (KDIGO)  

• Increase in serum creatinine by ≥ 0.3 mg/dL within 48 hrs, OR 
• Increase in serum creatinine to ≥ 1.5 times baseline within 7 days, OR 
• Urine output < 0.5 mL/kg/hr for 6 hrs 

Severity Staging 

• Stage 1: 1.5–1.9 × baseline creatinine or ≥ 0.3 mg/dL rise 
• Stage 2: 2.0–2.9 × baseline 
• Stage 3: ≥ 3 × baseline or creatinine ≥ 4.0 mg/dL or dialysis required 

CDI and Current Coding Guidance 

• Avoid vague terms like “renal insufficiency”; use “acute kidney injury” or “acute renal failure” (interchangeable per coding). 
• Always link AKI to the underlying cause (e.g., sepsis, dehydration, obstruction). 
• If ATN or AIN are present, document explicitly (these are MCCs). 
• Do not abbreviate AKI without context; clarify in the first mention. 
• Trend labs and urine output to support diagnosis before querying. 
• Assign code N17.0, Acute kidney failure with tubular necrosis, with a POA of N for documentation of a patient with AKI on admission who then develops ATN after admission. 
• For a case of acute kidney injury (AKI) due to acute tubular necrosis (ATN) secondary to contrast-induced nephropathy, the correct coding assignment is N17.0 for acute kidney failure with tubular necrosis, N14.11 for contrast-induced nephropathy, and T50.8X5A for adverse effect of diagnostic agents, initial encounter. This combination accurately reflects the underlying cause, the specific kidney injury type, and the adverse effect of the contrast agent. 

Pro Tip:

AKI impacts severity of illness and quality metrics (e.g., PSI-10 Post-Op AKI). Accurate documentation ensures correct DRG assignment and patient safety.