Mock Nephrology Module 1

A 68-year-old woman with a background of postmenopausal osteoporosis (T-score −3.2 at the femoral neck) presents to her general practitioner with a 6-week history of progressive fatigue, generalised muscle weakness, and bone pain. She received her second annual infusion of zoledronic acid (Aclasta) 5 mg approximately 8 weeks ago. She has no history of diabetes, myeloma, or prior renal disease. Her regular medications include cholecalciferol and a calcium supplement. She denies vomiting, diarrhoea, or diuretic use.

Physical examination reveals proximal muscle weakness but is otherwise unremarkable.

Investigations reveal:

Which of the following findings most strongly supports the underlying diagnosis?

A 28-year-old woman presents to her general practitioner with recurrent episodes of muscle cramps and fatigue. She denies any medication use, vomiting, or diarrhoea. Her blood pressure is 95/60 mmHg.

Investigations reveal:

• Serum sodium: 136 mmol/L (135–145)
• Serum potassium: 2.8 mmol/L (3.5–5.0)
• Serum chloride: 94 mmol/L (95–110)
• Serum bicarbonate: 32 mmol/L (22–32)
• Serum magnesium: 0.5 mmol/L (0.70–1.10)
• Serum calcium: 2.45 mmol/L (2.10–2.60)
• Urine calcium/creatinine ratio: low Urine chloride: 45 mmol/L

Which of the following is the most likely underlying molecular defect?

A 55-year-old man with type 2 diabetes mellitus and an eGFR of 55 mL/min/1.73m² (>90) is found to have persistent hyperkalaemia of 5.9 mmol/L (3.5–5.0) despite dietary counselling. His medications include metformin and perindopril.

Venous blood gas shows:

• pH 7.30 (7.35–7.45) 
• Bicarbonate of 18 mmol/L (22–32).
• The serum anion gap is 10 mmol/L (8–16).
• Urine pH is 5.2.

Which of the following best explains the pathophysiology of his acid-base disturbance?

A 42-year-old woman with a history of Sjögren syndrome presents with weakness and polyuria.

Investigations reveal:

• Serum sodium: 140 mmol/L (135–145)
• Serum potassium: 2.6 mmol/L (3.5–5.0)
• Serum chloride: 116 mmol/L (95–110)
• Serum bicarbonate: 14 mmol/L (22–32)
• Serum creatinine: 85 μmol/L (45–90)
• Urine pH: 6.8
• Renal ultrasound: bilateral medullary nephrocalcinosis

Which of the following best explains why this patient is predisposed to nephrocalcinosis?

A 60-year-old man with bipolar affective disorder managed with lithium for 20 years presents with polyuria (6 litres/day) and polydipsia.

Serum sodium is 148 mmol/L (135–145) and serum osmolality is 305 mOsm/kg (275–295).

Despite administration of desmopressin (DDAVP), urine osmolality remains at 180 mOsm/kg (300–900 after fluid restriction).

Which of the following best explains the mechanism of his polyuria?

A 52-year-old woman is found to have an incidental serum calcium of 2.72 mmol/L (2.10–2.60) on routine blood tests. She is asymptomatic.

Further investigations reveal:

• PTH: 7.2 pmol/L (1.6–6.9)
• Serum magnesium: 1.05 mmol/L (0.70–1.10)
• 24-hour urine calcium: 1.2 mmol/day (2.5–7.5)
• Urine calcium/creatinine clearance ratio: 0.005

Which of the following is the most appropriate next step in management?

A 45-year-old man presents with recurrent calcium oxalate renal calculi. He is started on hydrochlorothiazide 25 mg daily to reduce stone recurrence.

Which of the following best explains the mechanism by which thiazide diuretics reduce urinary calcium excretion?

A 68-year-old woman with chronic kidney disease stage 4 (eGFR 22 mL/min/1.73m²) has the following results:

• Serum calcium (corrected): 2.05 mmol/L (2.10–2.60)
• Serum phosphate: 2.1 mmol/L (0.8–1.5)
• PTH: 42 pmol/L (1.6–6.9)
• 25-hydroxyvitamin D: 55 nmol/L (>50)
• 1,25-dihydroxyvitamin D: 25 pmol/L (60–108)

Which of the following is the initial trigger for the development of secondary hyperparathyroidism in this patient?

A 34-year-old man is being investigated for recurrent hypokalaemia (K+ 2.9 mmol/L [3.5–5.0]). His blood pressure is 160/100 mmHg.

Venous blood gas shows pH 7.50 with bicarbonate of 34 mmol/L (22–32).

Serum aldosterone is markedly elevated and plasma renin activity is suppressed.

Which of the following mechanisms best explains the metabolic alkalosis in this patient?

A 48-year-old woman with multiple myeloma presents with generalised bone pain.

Investigations reveal:

• Serum potassium: 3.0 mmol/L (3.5–5.0)
• Serum bicarbonate: 15 mmol/L (22–32)
• Serum anion gap: 11 mmol/L (8–16)
• Urine pH: 5.0
• Serum phosphate: 0.6 mmol/L (0.8–1.5)
• Serum uric acid: 0.15 mmol/L (0.20–0.45)
• Urine glucose: 2+ (with normal serum glucose)

Which of the following is the most likely diagnosis?

A 3-week-old male infant presents with polyhydramnios detected antenatally, polyuria, failure to thrive, and hypercalciuria.

Investigations show:

• Serum potassium: 2.5 mmol/L (3.5–5.5 neonatal)
• Serum bicarbonate: 32 mmol/L (22–32)
• Blood pressure: low for age
• Serum calcium: 2.55 mmol/L (2.10–2.60)
• Urine calcium: markedly elevated

Which of the following molecular defects is most likely responsible for this presentation?

A 62-year-old man with a history of heart failure with reduced ejection fraction is commenced on high-dose furosemide for worsening peripheral oedema. After two weeks of therapy, his blood results show:

• Serum sodium: 133 mmol/L (135–145)
• Serum potassium: 2.8 mmol/L (3.5–5.0)
• Serum chloride: 88 mmol/L (95–110)
• Serum bicarbonate: 36 mmol/L (22–32)
• Serum magnesium: 0.55 mmol/L (0.70–1.10)
• Serum calcium: 2.05 mmol/L (2.10–2.60)

Which of the following best explains the hypomagnesaemia and hypocalcaemia in this patient?

A 70-year-old man with type 2 diabetes mellitus and hypertension has an eGFR of 45 mL/min/1.73m² (>90) and a urine albumin-to-creatinine ratio of 85 mg/mmol (<3.5).

He is commenced on an angiotensin receptor blocker (ARB). His repeat serum creatinine rises by 18% from baseline after two weeks.

Which of the following best explains the mechanism by which this medication reduces proteinuria in this patient?

A 50-year-old woman presents with generalised oedema, frothy urine, and fatigue.

Investigations reveal:

• Serum albumin: 18 g/L (35–50)
• 24-hour urine protein: 8.2 g/day (<0.15)
• Total cholesterol: 9.8 mmol/L (<5.5)
• Serum creatinine: 72 μmol/L (45–90)
• Urine microscopy: oval fat bodies, no red blood cell casts

Which of the following is the most accurate description of the pathophysiological mechanism leading to proteinuria in nephrotic syndrome?

A 35-year-old woman presents with episodic macroscopic haematuria coinciding with upper respiratory tract infections.

Urine microscopy shows dysmorphic red blood cells. Her serum creatinine is 95 μmol/L (45–90) and urine protein-to-creatinine ratio is 45 mg/mmol (<15).

Serum complement levels are normal.

Which of the following is the most common glomerular disease worldwide that best fits this clinical presentation?

A 58-year-old man with newly diagnosed type 2 diabetes mellitus is commenced on empagliflozin for glycaemic management.

His baseline eGFR is 75 mL/min/1.73m² (>90). After four weeks, his fasting blood glucose has improved and his blood pressure has decreased modestly.

Which of the following best describes the renal mechanism of action of empagliflozin?

A 40-year-old man is evaluated for hypertension and hypokalaemia. His blood pressure is 165/105 mmHg. Investigations reveal:

• Serum potassium: 3.0 mmol/L (3.5–5.0)
• Serum bicarbonate: 33 mmol/L (22–32)
• Urine potassium: 55 mmol/L (25–125)
• Urine chloride: 3 mmol/L (variable)

He admits to recurrent self-induced vomiting but denies diuretic use. A urine diuretic screen is negative.

Which of the following best explains the low urine chloride level in this patient?

A 72-year-old woman with osteoporosis is prescribed a thiazide diuretic for hypertension. Her treating physician advises her that this medication may have an additional benefit for her bone health. 

Which of the following best describes why thiazide diuretics are associated with reduced fracture risk?

A 55-year-old man with chronic kidney disease stage 3b (eGFR 38 mL/min/1.73m²) secondary to diabetic nephropathy has the following blood results:

• Serum potassium: 5.8 mmol/L (3.5–5.0)
• Venous blood gas pH: 7.28 (7.35–7.45)
• Serum bicarbonate: 16 mmol/L (22–32)
• Serum anion gap: 12 mmol/L (8–16)

His medications include ramipril, metformin, and ibuprofen as needed for knee pain. Blood pressure is 155/95 mmHg with peripheral oedema.

Which of the following is the most appropriate pharmacological intervention to address both the hyperkalaemia and acidosis?

A 30-year-old woman with systemic lupus erythematosus (SLE) presents with fatigue and is found to have:

• Serum potassium: 2.7 mmol/L (3.5–5.0)
• Serum bicarbonate: 14 mmol/L (22–32)
• Serum chloride: 118 mmol/L (95–110)
• Serum anion gap: 10 mmol/L (8–16)
• Urine pH: 7.0
• Serum creatinine: 80 μmol/L (45–90)
• Renal ultrasound: bilateral medullary nephrocalcinosis

She is commenced on oral potassium citrate supplementation.

Which of the following is the primary therapeutic rationale for using citrate-based alkali rather than sodium bicarbonate in this condition?

A 58-year-old man with biopsy-proven primary membranous nephropathy and anti-PLA2R antibody titre of 85 RU/mL is commenced on rituximab.

Six months later, his anti-PLA2R antibody is undetectable, but his urine protein-to-creatinine ratio (uPCR) remains at 280 mg/mmol (reference: <30 mg/mmol).

He is clinically well with stable eGFR of 62 mL/min/1.73m² and serum albumin 28 g/L (reference: 35–50 g/L).

What is the likely explanation for the discrepancy seen in his urine protein/creatinine ratio despite his clinical improvement?

A 45-year-old woman presents with bilateral lower limb oedema, uPCR 850 mg/mmol (reference: <30 mg/mmol), serum albumin 18 g/L (reference: 35–50 g/L), and eGFR 72 mL/min/1.73m².

Kidney biopsy confirms minimal change disease. She has a BMI of 38 kg/m² and is otherwise well with no prior thromboembolic history.

She is commenced on high-dose prednisolone.

Which of the following is the most appropriate thromboprophylaxis strategy?

A 32-year-old man is referred following an episode of macroscopic haematuria during an upper respiratory tract infection.

His blood pressure is 142/88 mmHg.

Investigations reveal:

• eGFR 78 mL/min/1.73m² (reference: >90 mL/min/1.73m²)
• uPCR 130 mg/mmol (approximately 1.3 g/day; reference: <30 mg/mmol)
• serum albumin 38 g/L (reference: 35–50 g/L)
• urine microscopy showing dysmorphic red blood cells
• Complement C3 and C4 are normal
• Kidney biopsy shows mesangial IgA deposits with mesangial hypercellularity (M1, E0, S0, T0, C0)

After initiation of maximum tolerated RAS blockade and blood pressure optimisation, which additional agent has the strongest evidence for slowing kidney disease progression in this patient?

A 68-year-old woman presents with a 6-week history of malaise, arthralgia, and haemoptysis. Examination reveals bilateral crackles and peripheral oedema.

Investigations show:

• creatinine 380 µmol/L (reference: 45–90 µmol/L)
• eGFR 11 mL/min/1.73m²
• urine microscopy with dysmorphic red blood cells and red cell casts
• CRP 85 mg/L (reference: <5 mg/L)
• positive MPO-ANCA
• Kidney biopsy demonstrates pauci-immune necrotising crescentic glomerulonephritis with crescents in 60% of glomeruli.

Which of the following is the most appropriate induction therapy?

A 48-year-old Aboriginal Australian man is referred with proteinuria of 1.8 g/day (uPCR 180 mg/mmol; reference: <30 mg/mmol), eGFR 52 mL/min/1.73m² (reference: >90 mL/min/1.73m²), and blood pressure 155/95 mmHg.

He has a BMI of 34 kg/m² and type 2 diabetes.

Kidney biopsy shows focal segmental glomerulosclerosis with segmental foot process effacement on electron microscopy. There is no diffuse foot process effacement.

What is the most likely pathogenic mechanism for this condition?

A 28-year-old woman with known systemic lupus erythematosus presents with facial oedema, blood pressure 148/92 mmHg.

Investigations:

• eGFR 55 mL/min/1.73m² (reference: >90 mL/min/1.73m²)
• uPCR 320 mg/mmol (reference: <30 mg/mmol)
• serum albumin 24 g/L (reference: 35–50 g/L)
• low C3 at 0.35 g/L (reference: 0.75–1.75 g/L), low C4 at 0.04 g/L (reference: 0.14–0.54 g/L)
• positive anti-dsDNA antibodies
• urine microscopy showing dysmorphic red blood cells.
• Kidney biopsy shows diffuse proliferative glomerulonephritis affecting >50% of glomeruli with subendothelial immune complex deposits and full-house immunostaining (IgG, IgA, IgM, C3, C1q).

Which of the following is the most appropriate initial immunosuppressive regimen?

A 25-year-old male smoker presents with haemoptysis and oliguria over 5 days.

Investigations reveal:

• creatinine 650 µmol/L (reference: 60–110 µmol/L)
• urine microscopy with red cell casts
• chest X-ray showing bilateral pulmonary infiltrates.
• Anti-GBM antibodies are strongly positive.
• ANCA is negative.
• Kidney biopsy demonstrates crescentic glomerulonephritis with linear IgG staining along the glomerular basement membrane.
• All glomeruli show crescent formation and 80% are globally sclerosed.

Which of the following statements regarding this patient’s management is most accurate?

A 22-year-old woman presents with hypertension, haematuria and proteinuria.

Investigations:

• Urine protein/creatinine ratio (uPCR) is 210 mg/mmol; reference: <30 mg/mmol)
• eGFR is 65 mL/min/1.73m² (reference: >90 mL/min/1.73m²).
• Serum C3 is 0.40 g/L (reference: 0.75–1.75 g/L)
• Serum C4 is 0.25 g/L (reference: 0.14–0.54 g/L)
• Serology for hepatitis B, hepatitis C, ANA, and ANCA are negative.
• Kidney biopsy shows a membranoproliferative pattern of injury with dominant C3 staining on immunofluorescence and minimal immunoglobulin deposition.

Which of the following is the most likely underlying pathogenic mechanism?

A 30-year-old woman was diagnosed with biopsy-proven minimal change disease 18 months ago and achieved complete remission with prednisone at a dose of 1 mg/kg/day.

She has since relapsed three times, each time requiring re-introduction of high-dose prednisone.

She now presents with a fourth relapse with uPCR 780 mg/mmol (reference: <30 mg/mmol) and serum albumin 20 g/L (reference: 35–50 g/L).

She has developed cushingoid features, has gained 15 kg, and her HbA1c is 7.2% (reference: <6.0%). Her eGFR is 92 mL/min/1.73m².

What is the most appropriate next step in management?

A 72-year-old man with type 2 diabetes and a chronic foot ulcer infected with methicillin-resistant Staphylococcus aureus (MRSA) is admitted with haematuria, hypertension (168/94 mmHg), and acute kidney injury with creatinine 310 µmol/L (reference: 60–110 µmol/L; baseline 95 µmol/L).

Urine microscopy shows dysmorphic red blood cells.

Serum C3 is low at 0.52 g/L (reference: 0.75–1.75 g/L) and C4 is normal.

Kidney biopsy shows endocapillary proliferative glomerulonephritis with IgA-dominant deposits and hump-shaped subepithelial deposits on electron microscopy.

Which of the following best describes the expected clinical course?