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Respiratory & Renal/Urinary Systems — Step 1 practice questions
246 questions in this area, with an explanation for every answer choice.
Three samples below, free and without an account.
How this shows up on Step 1
These two systems are examined together because acid-base links them. Expect to be handed a set of values and asked to name the disturbance, then explain the compensation. Renal physiology rewards knowing the nephron segment by segment, since most questions turn on where a drug or defect acts. Respiratory questions favour ventilation-perfusion reasoning and the mechanics of obstruction versus restriction.
Sample questions
Sample question 1
A 68-year-old man with long-standing diabetes has a normal anion gap metabolic acidosis with HYPERkalemia and a urine pH of 5.2. Plasma renin and aldosterone are low. Which of the following best explains his acidosis?
Explanations
A. Accumulation of unmeasured organic anions
Organic anions would raise the anion gap.
B. Inability of alpha-intercalated cells to secrete hydrogen ions, with alkaline urine
Distal (type 1) RTA causes hypokalemia and an inappropriately HIGH urine pH.
C. Hypoaldosteronism reduces distal sodium reabsorption and potassium secretion; the resulting hyperkalemia impairs renal ammoniagenesis and acid excretion · correct
Type 4 RTA is the most common RTA, typically from hyporeninemic hypoaldosteronism in diabetic nephropathy (also from ACE inhibitors, ARBs, NSAIDs, heparin, and potassium-sparing diuretics). Aldosterone deficiency causes hyperkalemia, and high intracellular potassium in proximal tubular cells suppresses ammonia production, limiting urinary buffering — so acid excretion falls despite the ability to acidify urine (pH <5.5). Treat with fludrocortisone or a low-potassium diet and loop diuretics.
D. Failure of proximal bicarbonate reabsorption
Proximal (type 2) RTA causes HYPOkalemia with a normal ability to acidify urine once bicarbonate is depleted.
E. Gastrointestinal bicarbonate loss from diarrhea
Diarrhea causes hypokalemic normal-gap acidosis with a negative urine anion gap.
Sample question 2
Two days after a motorcycle crash with bilateral femoral shaft fractures, a 26-year-old man develops hypoxemia, confusion, and a petechial rash over the chest and axillae. Platelet count is low. Which of the following is the most likely diagnosis?
Explanations
A. Fat embolism syndrome · correct
The triad of hypoxemia, neurologic changes, and a petechial rash 1–3 days after long-bone or pelvic fracture is fat embolism syndrome: marrow fat enters torn venules, lodges in the pulmonary (and, via shunts, systemic) microcirculation, and free fatty acids trigger inflammation and platelet consumption. Treatment is supportive; early fracture fixation reduces risk.
B. Meningococcemia
Meningococcemia produces fever, purpura, and shock without the fracture context.
C. Pulmonary thromboembolism
Thromboembolism causes hypoxemia and tachycardia but not petechiae or characteristic thrombocytopenia, and typically occurs later.
D. Thrombotic thrombocytopenic purpura
TTP has microangiopathic hemolysis, renal failure, and fever, and no relation to fractures.
E. Transfusion-related acute lung injury
TRALI occurs within 6 hours of transfusion, without rash.
Sample question 3
A patient started on a new antibiotic one week ago develops fever, a rash, and acute kidney injury. Urinalysis shows white blood cells and eosinophils without significant proteinuria. Which of the following is the most likely diagnosis?
Explanations
A. Diabetic nephropathy
Diabetic nephropathy is a chronic process unrelated to a recent new medication trigger.
B. Acute tubular necrosis
ATN shows muddy brown casts, not this eosinophiluria/fever/rash pattern tied to a new medication.
C. Acute interstitial nephritis · correct
Fever, rash, and eosinophiluria following a new medication (a hypersensitivity reaction) are classic for acute interstitial nephritis, commonly caused by drugs like penicillins, NSAIDs, and sulfonamides.
D. Renal artery stenosis
Renal artery stenosis presents with hypertension and does not show this eosinophiluria/hypersensitivity pattern.
E. Minimal change disease
Minimal change disease presents with nephrotic-range proteinuria, not this eosinophiluria/hypersensitivity pattern.
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