Renal and Genitourinary
What you must know
Acute kidney injury is staged by creatinine rise and urine output and sorted into prerenal, intrinsic, and postrenal causes. Prerenal states improve with volume; fractional excretion of sodium under 1% suggests it, but diuretics, ACE inhibitors, and contrast make the index unreliable. Acute interstitial nephritis shows rash, fever, eosinophilia, and sterile pyuria after a new drug. Postrenal obstruction is excluded with a bladder scan and renal ultrasound - hydronephrosis plus rising creatinine means relieve the obstruction. Know indications for dialysis: acidosis, electrolytes (refractory hyperkalemia), intoxication, overload, uremia (AEIOU).
Chronic kidney disease is staged by GFR category plus albuminuria; manage blood pressure, use an ACE inhibitor or ARB for albuminuria, add an SGLT2 inhibitor, and watch for anemia, metabolic acidosis, and CKD-mineral bone disease. Nephrotic syndrome (proteinuria over 3.5 g/day, hypoalbuminemia, edema) versus nephritic syndrome (hematuria, red cell casts, hypertension) guides the differential. Post-streptococcal glomerulonephritis follows pharyngitis or impetigo by one to three weeks with low complement.
Stones: calcium oxalate predominates; CT is the test of choice; alpha-blockers assist passage of distal ureteral stones. Upper tract infection with fever and flank pain is pyelonephritis - treat systemically and image if obstructed or not improving. Benign prostatic hyperplasia: alpha-blocker for rapid symptom relief, 5-alpha reductase inhibitor for larger glands over months; red flags include retention, hematuria, and recurrent infection. Asymptomatic bacteriuria is not treated except in pregnancy or before urologic procedures.
Traps
- Giving intravenous contrast to a patient with AKI when a noncontrast study answers the question.
- Relying on fractional excretion of sodium in a patient on diuretics.
- Treating asymptomatic bacteriuria in an older adult.
- Missing obstruction in a patient who is not improving on antibiotics.
Rule of thumb
Acute kidney injury plus hydronephrosis is postrenal until proven otherwise - bladder scan, then relieve the obstruction.