Internal Medicine Exam Nephrology and Kidney Injury 3 — Questions and Answers
Question 1: A 55-year-old woman with type 2 diabetes has a GFR of 28 mL/min/1.73m² and serum phosphorus of 6.1 mg/dL despite dietary restriction. What is the most appropriate next step?
- Start calcium carbonate with meals
- Start sevelamer (non-calcium binder) (Correct answer)
- Initiate dialysis
- Increase dietary protein
Correct answer: Start sevelamer (non-calcium binder)
Sevelamer is preferred over calcium-based binders in dialysis-stage CKD to avoid calcium loading and vascular calcification risk.
Question 2: A 40-year-old man is found to have a serum sodium of 118 mEq/L. He has psychogenic polydipsia and appears euvolemic. Which correction rate is safe to prevent osmotic demyelination syndrome?
- Correct by 20 mEq/L in 24 hours
- Correct by 8-10 mEq/L in 24 hours (Correct answer)
- Correct by 15 mEq/L in 8 hours
- Correct by 12 mEq/L in 6 hours
Correct answer: Correct by 8-10 mEq/L in 24 hours
Safe correction of chronic hyponatremia is limited to 8-10 mEq/L per 24 hours to prevent osmotic demyelination syndrome (central pontine myelinolysis).
Question 3: A 70-year-old man with decompensated heart failure has oliguria, BUN 48 mg/dL, creatinine 2.2 mg/dL, and urine sodium 10 mEq/L. His kidney injury is best classified as:
- Intrinsic AKI from ischemic ATN
- Post-renal AKI from urethral obstruction
- Pre-renal AKI from reduced effective circulating volume (Correct answer)
- Cardiorenal syndrome type 3
Correct answer: Pre-renal AKI from reduced effective circulating volume
Low urine sodium (<20 mEq/L) and elevated BUN:creatinine ratio in heart failure indicate pre-renal AKI from reduced effective arterial blood volume.
Question 4: A 50-year-old woman with a history of recurrent UTIs presents with flank pain and imaging showing a staghorn calculus filling the right renal pelvis. Urine culture grows Proteus mirabilis. What type of stone is this?
- Calcium oxalate
- Uric acid
- Struvite (magnesium ammonium phosphate) (Correct answer)
- Cystine
Correct answer: Struvite (magnesium ammonium phosphate)
Struvite stones form in the setting of urease-producing organisms (Proteus, Klebsiella) that alkalinize urine, causing precipitation of magnesium ammonium phosphate.
Question 5: A patient with nephrotic syndrome develops sudden flank pain and hematuria. CT shows right renal vein thrombosis. Which underlying condition most predisposes to renal vein thrombosis in nephrotic syndrome?
- IgA nephropathy
- Membranous nephropathy (Correct answer)
- Minimal change disease
- FSGS
Correct answer: Membranous nephropathy
Membranous nephropathy has the highest risk of renal vein thrombosis among nephrotic syndromes due to urinary loss of anticoagulant proteins (antithrombin III, protein C/S).
Question 6: A 25-year-old man presents with episodic gross hematuria 1-2 days after upper respiratory infections. Renal biopsy shows mesangial IgA deposits. What is the most likely diagnosis?
- Post-streptococcal GN
- IgA nephropathy (Berger disease) (Correct answer)
- Henoch-Schönlein purpura nephritis
- Thin basement membrane disease
Correct answer: IgA nephropathy (Berger disease)
Synpharyngitic hematuria (hematuria concurrent with URI, not 2-3 weeks later) with mesangial IgA deposits is the hallmark of IgA nephropathy.
Question 7: A 68-year-old woman with osteoporosis takes high-dose vitamin D supplements. She now has polyuria, polydipsia, constipation, confusion, and serum calcium of 13.2 mg/dL. Her PTH is suppressed. The most likely mechanism of hypercalcemia is:
- Primary hyperparathyroidism
- Malignancy-associated PTHrP release
- Vitamin D toxicity causing excess intestinal calcium absorption (Correct answer)
- Milk-alkali syndrome
Correct answer: Vitamin D toxicity causing excess intestinal calcium absorption
Vitamin D toxicity increases intestinal calcium absorption via 1,25(OH)2D, causing hypercalcemia with suppressed PTH.
Internal Medicine Exam Nephrology and Kidney Injury 3
A 55-year-old woman with type 2 diabetes has a GFR of 28 mL/min/1.73m² and serum phosphorus of 6.1 mg/dL despite dietary restriction.
What is the most appropriate next step?