The clinician differentiates acute kidney injury from chronic kidney disease using clinical, laboratory, and imaging criteria, recognizing that acute-on-chronic kidney disease (AKI superimposed on pre-existing CKD) is common. Findings suggesting CKD (indicating chronicity): small kidney size bilaterally on ultrasound (less than 9 cm, indicating cortical atrophy from chronic nephron loss), increased cortical echogenicity, presence of anemia of chronic disease (decreased erythropoietin production), secondary hyperparathyroidism (elevated PTH with low calcium and elevated phosphorus from impaired calcitriol synthesis and phosphorus retention), and metabolic bone disease. Findings suggesting AKI: normal kidney size or enlarged kidneys (swelling from acute inflammation), baseline creatinine available showing recent rise, preserved hemoglobin initially (anemia from decreased EPO takes weeks to develop), and potentially reversible with appropriate treatment. CKD staging uses the KDIGO classification based on GFR category (G1: greater than or equal to 90, G2: 60-89, G3a: 45-59, G3b: 30-44, G4: 15-29, G5: less than 15 mL/min/1.73m2) and albuminuria category (A1: less than 3 mg/mmol, A2: 3-30, A3: greater than 30 mg/mmol). The clinician manages CKD progression through blood pressure optimization (target less than 130/80 with ACEI or...