Free Internal Medicine Nephrology and Kidney Injury Questions and Answers — Questions and Answers
Question 1: A 72-year-old male with CKD stage 4, diabetes, and hypertension is brought to the emergency department with generalized weakness. His medications include lisinopril and spironolactone. An ECG shows peaked T-waves and a widened QRS complex. His serum potassium is 7.2 mEq/L. What is the most appropriate initial step in management?
- Administer intravenous insulin and glucose
- Administer intravenous calcium gluconate (Correct answer)
- Initiate emergent hemodialysis
- Administer an oral potassium-binding resin
Correct answer: Administer intravenous calcium gluconate
In a patient with severe hyperkalemia and ECG changes indicating cardiac membrane instability (peaked T-waves, widened QRS), the immediate priority is to stabilize the cardiac membrane to prevent life-threatening arrhythmias. Intravenous calcium gluconate directly antagonizes the membrane-depolarizing effects of hyperkalemia and works within minutes. While insulin/glucose, dialysis, and binding resins are all effective at lowering total body potassium, they take longer to act and do not provide immediate cardioprotection.
Question 2: A 65-year-old female with a history of hypertension presents with new-onset peripheral edema, fatigue, and 8 grams of proteinuria on a 24-hour urine collection. Her serum creatinine is 1.4 mg/dL and albumin is 2.5 g/dL. A renal biopsy is performed. Which of the following is the most common cause of primary nephrotic syndrome in non-diabetic White adults?
- Focal Segmental Glomerulosclerosis (FSGS)
- Minimal Change Disease
- IgA Nephropathy
- Membranous Nephropathy (Correct answer)
Correct answer: Membranous Nephropathy
Membranous nephropathy is the leading cause of primary nephrotic syndrome in non-diabetic White adults. It is an autoimmune disease characterized by the deposition of immune complexes along the glomerular basement membrane. While FSGS is another common cause, it is more prevalent in other populations. Minimal Change Disease is the most common cause in children, and IgA nephropathy typically presents as nephritic syndrome or asymptomatic hematuria.
Question 3: A 58-year-old male with a 15-year history of poorly controlled type 2 diabetes and CKD stage 3 is noted to have a persistent, non-anion gap metabolic acidosis and a serum potassium of 5.8 mEq/L despite dietary counseling. His urine pH is 5.0. Which of the following is the most likely diagnosis?
- Type 1 (Distal) Renal Tubular Acidosis
- Type 2 (Proximal) Renal Tubular Acidosis
- Type 4 (Hyperkalemic) Renal Tubular Acidosis (Correct answer)
- Diabetic Ketoacidosis
Correct answer: Type 4 (Hyperkalemic) Renal Tubular Acidosis
This patient's presentation of non-anion gap metabolic acidosis, persistent hyperkalemia, and an appropriately acidic urine pH (<5.5) in the setting of diabetic nephropathy is classic for Type 4 Renal Tubular Acidosis. This condition results from aldosterone deficiency or resistance, which impairs distal nephron secretion of both potassium and hydrogen ions. Type 1 RTA is associated with hypokalemia and an inability to acidify the urine. Type 2 RTA is also associated with hypokalemia. Diabetic ketoacidosis would present with a high anion gap.
Question 4: A 45-year-old man is hospitalized for community-acquired pneumonia and treated with intravenous piperacillin-tazobactam. Ten days later, his serum creatinine rises from a baseline of 1.0 mg/dL to 3.5 mg/dL. Urinalysis reveals white blood cells, red blood cells, and white blood cell casts. A peripheral blood smear shows eosinophilia. Which of the following is the most likely cause of his acute kidney injury?
- Acute Tubular Necrosis (ATN)
- Acute Interstitial Nephritis (AIN) (Correct answer)
- Prerenal Azotemia
- Postrenal Obstruction
Correct answer: Acute Interstitial Nephritis (AIN)
The clinical picture of a delayed rise in creatinine following exposure to a new drug (especially an antibiotic), along with urinalysis findings of sterile pyuria (WBCs) and WBC casts, and peripheral eosinophilia, is highly characteristic of drug-induced Acute Interstitial Nephritis (AIN). AIN is a hypersensitivity reaction in the renal interstitium. ATN typically presents with muddy brown casts, prerenal azotemia would show a bland sediment, and postrenal obstruction is unlikely without corresponding symptoms or imaging findings.
Question 5: Which of the following findings is an absolute indication for initiating urgent hemodialysis in a patient with acute kidney injury?
- Serum creatinine of 8.0 mg/dL
- Blood Urea Nitrogen (BUN) of 120 mg/dL
- Uremic pericarditis with a friction rub (Correct answer)
- Urine output of 300 mL in 24 hours
Correct answer: Uremic pericarditis with a friction rub
The development of uremic complications, such as pericarditis or encephalopathy, is an absolute indication for urgent hemodialysis, regardless of the specific BUN or creatinine values. While high creatinine and BUN levels are concerning and often accompany the need for dialysis, they are not, in themselves, absolute indications. The decision is based on life-threatening clinical manifestations, which also include refractory severe metabolic acidosis, severe hyperkalemia, or refractory fluid overload.
Question 6: A 28-year-old male presents with an episode of gross hematuria that occurred two days after the onset of an upper respiratory tract infection. He has had similar episodes in the past. His blood pressure is 135/85 mmHg, and serum creatinine is 1.1 mg/dL. Urinalysis confirms hematuria and shows 1+ proteinuria. Which of the following is the most likely diagnosis?
- Post-streptococcal glomerulonephritis
- IgA Nephropathy (Berger's Disease) (Correct answer)
- Henoch-Schönlein Purpura (HSP)
- Minimal Change Disease
Correct answer: IgA Nephropathy (Berger's Disease)
IgA Nephropathy is the most common cause of primary glomerulonephritis worldwide and classically presents as recurrent episodes of macroscopic hematuria that occur concurrently with or within a few days of a mucosal infection (synpharyngitic hematuria). Post-streptococcal glomerulonephritis typically has a latent period of 1-3 weeks after the infection. HSP (now called IgA vasculitis) is histologically similar but is a systemic vasculitis that would also involve purpura, arthralgias, or abdominal pain. Minimal Change Disease presents with nephrotic syndrome, not gross hematuria.
