A 60-year-old male with history of benign prostatic hypertrophy presents complaining of nausea and vomiting. Laboratory values include serum Na of 145 mmol/L, blood urea nitrogen (BUN) of 45 mg/dL, creatinine of 2.0 mg/dL, urine Na of 10, and urine creatinine of 80. Which of the following is the MOST likely diagnosis?

Correct Answer: A

Rationale: Prerenal failure fits BUN:creatinine >20:1 (22.5), urine Na <20 (10), high urine:serum creatinine (>40:1), dehydration from vomiting/BPH obstruction. ATN shows FENa >1, urine Na >40 tubular damage. Glomerulonephritis has casts absent here. Postrenal (BPH) raises creatinine more obstruction incomplete. Prerenal markers distinguish it, key to hypoperfusion diagnosis, unlike intrinsic or obstructive patterns.

Correct Answer: D

Rationale: Juxtaglomerular (JG) cells secrete renin, not mesangial (support), phagocytic, lacis (extraglomerular), or Na-sensitive (macula densa). This identifies JG cells' role in RAAS, critical for blood pressure regulation, contrasting with other glomerular components' functions.

Correct Answer: B

Rationale: Proteus causes UTI, is urease positive, and swarms, but is Gram-negative not Gram-positive. This corrects bacteriology, key for infection treatment, contrasting with Gram-positive misidentification.

Correct Answer: A

Rationale: Nosocomial UTIs involve Pseudomonas, Klebsiella, and Enterococcus not S. saprophyticus (community-acquired). This distinguishes hospital pathogens, key for infection control, contrasting with outpatient bacteria.

Correct Answer: D

Rationale: Both feature immune complex deposits not self-limiting (membranous chronic), nephrotic (membranous mainly), pediatric (PSGN mainly), or post-infectious (PSGN only). This identifies shared pathology, key for glomerulonephritis, contrasting with clinical differences.