From the Guidelines
Distinguishing between Acute Kidney Injury (AKI) and Chronic Kidney Disease (CKD) is crucial, as AKI may be reversible with proper treatment, whereas CKD represents permanent kidney damage requiring long-term management. To differentiate between AKI and CKD, specific laboratory tests and clinical assessments are necessary. For AKI, look for a rapid rise in serum creatinine (≥0.3 mg/dL within 48 hours or ≥50% increase from baseline within 7 days) and decreased urine output (<0.5 mL/kg/hr for 6+ hours), as defined by the KDIGO guidelines 1. Additional AKI markers include elevated BUN, hyperkalemia, metabolic acidosis, and normal-sized kidneys on imaging. CKD, on the other hand, is characterized by persistent abnormalities lasting >3 months, including:
- GFR <60 mL/min/1.73m²
- Albuminuria (>30 mg/day)
- Urine sediment abnormalities
- Electrolyte disturbances due to tubular disorders
- Histological abnormalities
- Structural abnormalities detected by imaging, such as small, scarred kidneys 1. CKD labs typically show gradually increasing creatinine, stable anemia, secondary hyperparathyroidism with elevated PTH. The distinction between AKI and CKD matters, as AKI may be reversible with proper treatment of the underlying cause, while CKD represents permanent kidney damage requiring long-term management strategies to slow progression 1. Some key differences between AKI and CKD include:
- Duration of kidney dysfunction: AKI is an abrupt decline in kidney function, whereas CKD is a gradual decline over months to years
- Reversibility: AKI may be reversible with proper treatment, whereas CKD is often irreversible
- Clinical presentation: AKI often presents with acute symptoms, such as oliguria, hyperkalemia, and metabolic acidosis, whereas CKD is often asymptomatic in its early stages. In clinical practice, it is essential to consider the patient's medical history, physical examination, and laboratory results to accurately diagnose and manage AKI and CKD, as highlighted in the acr appropriateness criteria® renal failure study 1.
From the Research
AKI vs CKD Labs
- The key laboratory indicator for Acute Kidney Injury (AKI) is an increase in serum creatinine or a decrease in urine output over hours to days 2, 3.
- The Kidney Disease: Improving Global Outcomes (KDIGO) defines AKI as an increase in the serum creatinine level of 0.3 mg/dL or more within 48 hours, an increase of 1.5 times or more of the baseline level within 7 days, or a decrease in urine output to less than 0.5 mL/kg/hour for 6 hours 3.
- Chronic Kidney Disease (CKD) is associated with an increased risk of AKI, and AKI can also accelerate the progression of CKD 4.
- Serum creatinine remains a key determinant in the management of renal dysfunction, and higher serum creatinine levels have been paradoxically associated with better patient survival in severe AKI 5.
- The etiology of AKI is conceptually classified into three general categories: prerenal, intrarenal, and postrenal, and AKI has mostly multifactorial pathophysiologic features 6.
- Urinalysis with microscopy can help narrow the differential diagnosis of AKI, and determining the cause of AKI is critical when possible 3.