From the Guidelines
To distinguish chronic kidney disease (CKD) from acute kidney injury (AKI), assess creatinine and Glomerular Filtration Rate (GFR) over time, with CKD diagnosed if abnormalities persist for >3 months and AKI characterized by a sudden increase in creatinine or rapid decline in GFR. The diagnosis of CKD and AKI can be made based on the following criteria:
- CKD:
- GFR <60 mL/min/1.73m2 for >3 months 1
- Elevated creatinine and BUN
- Stable or gradual decline in kidney function
- AKI:
- Sudden increase in creatinine (≥0.3 mg/dL within 48 hours) 1
- Rapid decline in GFR
- Urine output <0.5 mL/kg/hour for 6 hours Key steps in diagnosis include:
- Checking baseline kidney function if available
- Repeating tests after 1-2 weeks to assess for improvement
- Considering kidney ultrasound to evaluate for structural abnormalities It is essential to note that CKD is typically irreversible, while AKI may be reversible if the underlying cause is addressed promptly, as highlighted in the KDIGO guidelines 1. Early detection and management are crucial for both conditions to prevent further kidney damage and complications.
From the Research
Distinguishing Chronic Kidney Disease (CKD) from Acute Kidney Injury (AKI)
To distinguish CKD from AKI, several factors and measurements can be considered, including creatinine (Cr) levels and Glomerular Filtration Rate (GFR). The following points outline the key considerations:
- Estimating GFR: The initial assessment of GFR can be done by measuring serum creatinine and reporting estimated GFR based on serum creatinine (eGFRcr) using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2009 equation 2.
- Using Cystatin C: If confirmation of GFR is required, cystatin C should be measured, and estimated GFR should be calculated and reported using cystatin C (eGFRcys) and serum creatinine (eGFRcr-cys) or GFR should be measured directly using a clearance procedure 2, 3.
- Kinetic GFR (kGFR): kGFR is an estimate of immediate biomarker clearance derived from two discreet measurements and may better represent acute function in acutely unwell patients with rapidly changing renal function 4.
- Comparison of GFR Estimation: Studies have compared GFR estimation using serum creatinine (SCr) and cystatin C (CysC) in detecting CKD after an AKI event, showing that CysC detects more CKD events compared to SCr in the follow-up phase 5.
- Relationship between Serum Creatinine and eGFR: In patients with CKD, hypercreatininemia is associated with a low level of estimated glomerular filtration rate (eGFR), highlighting the importance of routine estimation of these parameters for prevention of complications related to CKD 6.
Key Considerations for Distinguishing CKD from AKI
- Acute vs. Chronic Conditions: AKI is characterized by a rapid decline in kidney function, whereas CKD is a gradual loss of kidney function over time.
- GFR and Creatinine Levels: eGFR and serum creatinine levels can help distinguish between AKI and CKD, with AKI typically showing a more rapid decline in GFR and increase in creatinine levels.
- Biomarkers and Estimation Equations: The use of cystatin C and kinetic GFR can provide additional information for distinguishing between AKI and CKD, especially in cases where serum creatinine is not reliable.