Assessment and Diagnosis
This domain tests whether you can build a defensible nephrology diagnosis: correct CKD staging, precise AKI criteria, and a workup that separates glomerular, tubular, and vascular disease before treatment starts.
Stage CKD on two axes, not one
CKD requires a marker of kidney damage (albuminuria, hematuria, structural or biopsy abnormality) or eGFR below 60 for at least 3 months. Report both: G1 ≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 <15 mL/min/1.73 m². Albuminuria: A1 <30, A2 30–300, A3 >300 mg/g creatinine on a spot urine albumin-to-creatinine ratio, confirmed on a first-morning specimen.
Apply KDIGO AKI criteria exactly
AKI is any of: creatinine rise ≥0.3 mg/dL within 48 hours; ≥1.5 times baseline within 7 days; or urine output <0.5 mL/kg/h for 6 hours. Stage by both creatinine and urine output and assign the worse stage.
Worked example
A 58-year-old with type 2 diabetes has eGFR 38 mL/min/1.73 m² and UACR 350 mg/g. That is G3b A3 - the very-high-risk cell of the KDIGO heat map. The exam answer is not "stage 3 CKD"; it is the full G/A designation plus what it triggers: maximized RAAS blockade, an SGLT2 inhibitor, blood pressure and glucose control, and nephrology referral.
Traps that cost marks
Normal eGFR does not exclude CKD - A3 albuminuria with eGFR 95 is still CKD. Never stage on a creatinine drawn during acute illness or after heavy exercise. Fractional excretion of sodium is unreliable on diuretics; use the clinical volume assessment instead. Hematuria with red cell casts or dysmorphic red cells points to glomerulonephritis, not urinary infection.