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Question 1Renal Anatomy, Physiology, and Pathophysiology

Which cell type forms the visceral layer of Bowman's capsule and provides the slit diaphragms of the glomerular filtration barrier?

  1. Parietal epithelial cell
  2. Podocyte Correct answer.
  3. Macula densa cell
  4. Mesangial cell

Explanation

Podocytes extend primary and secondary processes whose foot processes interdigitate over the glomerular basement membrane; the filtration slits between them are bridged by slit diaphragms made largely of nephrin and podocin, which restrict passage of albumin. Effacement of foot processes is the structural correlate of nonselective proteinuria.

Question 2Renal Anatomy, Physiology, and Pathophysiology

What is the approximate glomerular filtration rate in a healthy young adult?

  1. 600 mL/min
  2. 300 mL/min
  3. 125 mL/min Correct answer.
  4. 25 mL/min

Explanation

Normal GFR is about 125 mL/min, which corresponds to roughly 180 L of ultrafiltrate per day, of which more than 99% is reabsorbed. Renal plasma flow is about 600 mL/min, so only about one fifth of the plasma delivered is filtered.

Question 3Renal Anatomy, Physiology, and Pathophysiology

Renin is synthesized, stored, and released by which cells?

  1. Mesangial cells
  2. Granular cells Correct answer.
  3. Podocytes
  4. Macula densa cells

Explanation

Granular (juxtaglomerular) cells in the wall of the afferent arteriole contain renin in secretory granules and release it in response to reduced renal perfusion pressure, reduced NaCl delivery, and sympathetic beta-1 stimulation. Renin catalyzes the conversion of angiotensinogen to angiotensin I, the rate-limiting step of the renin-angiotensin-aldosterone system.

Question 4Renal Anatomy, Physiology, and Pathophysiology

Which hormone is produced by the kidney and stimulates erythrocyte production in bone marrow?

  1. Thrombopoietin
  2. Renin
  3. Erythropoietin Correct answer.
  4. Calcitriol

Explanation

Peritubular interstitial fibroblasts in the renal cortex sense tissue hypoxia and secrete erythropoietin, which drives erythroid progenitor proliferation and differentiation. Chronic kidney disease therefore causes a normocytic, normochromic anemia that responds to erythropoiesis-stimulating agents.

Question 5Renal Anatomy, Physiology, and Pathophysiology

How are the kidneys positioned within the abdomen?

  1. Within the peritoneal cavity behind the stomach
  2. Intraperitoneal, suspended by the mesentery
  3. Subperitoneal, enclosed within the rectus sheath
  4. Retroperitoneal, behind the parietal peritoneum Correct answer.

Explanation

The kidneys lie retroperitoneally against the posterior abdominal wall, with the peritoneum covering only their anterior surfaces. Because of this position, renal pain is often felt in the flank and kidneys can be approached surgically through the posterior lumbar region.

Question 6Renal Anatomy, Physiology, and Pathophysiology

What fraction of the resting cardiac output do both kidneys together receive?

  1. About 5% of cardiac output
  2. About 20% of cardiac output Correct answer.
  3. About 50% of cardiac output
  4. About 70% of cardiac output

Explanation

The kidneys together receive roughly 20-25% of resting cardiac output, about 1.1 L/min, despite representing less than 1% of body weight. Most of this flow goes to the cortex to support high rates of glomerular filtration and tubular reabsorption.

Question 7Renal Anatomy, Physiology, and Pathophysiology

The bulk of filtered glucose is reabsorbed in which nephron segment?

  1. Proximal convoluted tubule Correct answer.
  2. Medullary collecting duct
  3. Distal convoluted tubule of the nephron
  4. Thin descending limb of the loop of Henle

Explanation

Approximately 90% of filtered glucose is reclaimed in the early proximal convoluted tubule, mainly by the sodium-glucose cotransporter SGLT2 in the apical membrane with exit through GLUT2 basolaterally. The remaining glucose is absorbed by SGLT1 further along the proximal tubule, so no glucose normally appears in urine.

Question 8Renal Anatomy, Physiology, and Pathophysiology

Antidiuretic hormone acting on the collecting duct produces which change?

  1. Increased urea secretion into the tubular lumen
  2. Increased water permeability of the apical membrane Correct answer.
  3. Reduced medullary interstitial osmolarity
  4. Increased sodium reabsorption through apical ENaC channels

Explanation

ADH binds V2 receptors on principal cells, raising cAMP and driving insertion of aquaporin-2 channels into the apical membrane; water then flows down the medullary osmotic gradient and is reabsorbed. The result is concentrated urine and reduced free water clearance.

Question 9Renal Anatomy, Physiology, and Pathophysiology

If glomerular filtration rate is 125 mL/min and renal plasma flow is 625 mL/min, what is the filtration fraction?

  1. 0.80
  2. 0.20 Correct answer.
  3. 0.45
  4. 0.08

Explanation

Filtration fraction equals GFR divided by renal plasma flow, so 125/625 = 0.20, meaning about 20% of the plasma entering the glomerulus is filtered. Filtration fraction rises when efferent arteriolar tone increases and falls when afferent dilation or a fall in plasma oncotic pressure predominates.

Question 10Renal Anatomy, Physiology, and Pathophysiology

An increase in NaCl delivery to the macula densa triggers which response?

  1. Constriction of the afferent arteriole Correct answer.
  2. Reduced sodium reabsorption in the proximal tubule
  3. Dilation of the afferent arteriole
  4. Increased renin release from granular cells

Explanation

Tubuloglomerular feedback senses luminal NaCl via the Na-K-2Cl cotransporter in macula densa cells; increased delivery causes adenosine-mediated constriction of the afferent arteriole, lowering glomerular pressure and GFR. The same signal suppresses renin release from adjacent granular cells.

Question 11Renal Anatomy, Physiology, and Pathophysiology

A rise in hydrostatic pressure within Bowman's space has which effect on glomerular filtration?

  1. Decreases net filtration pressure and GFR Correct answer.
  2. Has no effect on GFR because it is a distal pressure
  3. Increases GFR by raising oncotic pressure
  4. Increases net filtration pressure and GFR

Explanation

Net filtration pressure equals glomerular capillary hydrostatic pressure minus Bowman's space hydrostatic pressure minus plasma oncotic pressure. Any rise in capsular pressure therefore opposes filtration and lowers GFR, as occurs in ureteral obstruction or acute tubular necrosis with tubular back-leak.

Question 12Renal Anatomy, Physiology, and Pathophysiology

A patient with bilateral renal artery stenosis is started on an ACE inhibitor. What is the expected effect on glomerular filtration?

  1. A rise in GFR because afferent arteriolar tone falls
  2. No change in GFR because autoregulation is intact
  3. A fall in GFR only when the drug is combined with a diuretic
  4. A fall in GFR because efferent arteriolar constriction is lost Correct answer.

Explanation

In renal artery stenosis, glomerular capillary pressure and GFR are maintained by angiotensin II-mediated efferent arteriolar constriction. Blocking angiotensin II formation removes this compensatory constriction, so GFR falls and creatinine rises, which is why ACE inhibitors are used cautiously in bilateral disease.

Question 13Renal Anatomy, Physiology, and Pathophysiology

At approximately what plasma glucose concentration does glucose first appear in the urine of a healthy adult?

  1. 180 to 200 mg/dL Correct answer.
  2. 80 to 100 mg/dL
  3. 400 to 500 mg/dL
  4. 250 to 300 mg/dL

Explanation

The renal threshold for glucose is about 180-200 mg/dL, the plasma level at which filtered glucose exceeds the transport maximum of the proximal tubular cotransporters. Filtered glucose begins to escape into urine at this threshold, and the resulting splay reflects heterogeneity of nephron transport capacity.

Question 14Renal Anatomy, Physiology, and Pathophysiology

A 5-year-old boy presents with periorbital edema, hypoalbuminemia, and heavy selective albuminuria. Light microscopy of the glomerulus is normal. Which diagnosis is most likely?

  1. Minimal change disease Correct answer.
  2. IgA nephropathy
  3. Membranous nephropathy
  4. Focal segmental glomerulosclerosis

Explanation

Minimal change disease is the most common cause of nephrotic syndrome in children; light microscopy is normal, while electron microscopy shows diffuse foot process effacement. It produces selective albuminuria and usually responds promptly to corticosteroids.

Question 15Renal Anatomy, Physiology, and Pathophysiology

Which complement finding is most characteristic of acute post-streptococcal glomerulonephritis?

  1. Normal complement levels throughout
  2. Elevated serum C3
  3. Normal C3 with low C4
  4. Low serum C3 with normal C4 Correct answer.

Explanation

Post-streptococcal glomerulonephritis activates the alternative complement pathway, so C3 is depressed while C4 remains normal. The hypocomplementemia resolves within about 6-8 weeks, and persistence beyond that should prompt consideration of an alternative diagnosis.

Question 16Renal Anatomy, Physiology, and Pathophysiology

Furosemide produces its diuretic effect by inhibiting which transporter?

  1. Na-Cl cotransporter (NCC) in the distal tubule
  2. Sodium-glucose cotransporter 2 (SGLT2)
  3. Na-K-2Cl cotransporter (NKCC2) Correct answer.
  4. Epithelial sodium channel (ENaC) in the collecting duct

Explanation

Loop diuretics block NKCC2 in the apical membrane of the thick ascending limb, abolishing both the diluting segment and the generation of the medullary osmotic gradient. This produces the most powerful natriuresis of any diuretic class and also increases calcium and magnesium excretion.

Question 17Renal Anatomy, Physiology, and Pathophysiology

The calcium-sparing effect of thiazide diuretics results from enhanced calcium reabsorption in which segment?

  1. Medullary collecting duct
  2. Proximal convoluted tubule
  3. Thick ascending limb of the loop of Henle
  4. Distal convoluted tubule Correct answer.

Explanation

Thiazides block NCC in the distal convoluted tubule, lowering intracellular sodium and driving basolateral sodium-calcium exchange while apical TRPV5 channels increase calcium entry. The net effect is reduced urinary calcium and higher serum calcium, which is useful in calcium stone formers and osteoporosis.

Question 18Renal Anatomy, Physiology, and Pathophysiology

Aldosterone enhances sodium reabsorption in the collecting duct mainly by which action?

  1. Inserting aquaporin-2 water channels
  2. Increasing the number of apical ENaC channels Correct answer.
  3. Inhibiting the basolateral Na/K-ATPase
  4. Stimulating the Na-K-2Cl cotransporter in the thick ascending limb

Explanation

Aldosterone binds mineralocorticoid receptors in principal cells and increases transcription of ENaC subunits and the basolateral Na/K-ATPase, raising sodium reabsorption and generating a lumen-negative potential that drives potassium and hydrogen secretion. Loss of this pathway explains the hyperkalemia of hypoaldosteronism.

Question 19Renal Anatomy, Physiology, and Pathophysiology

Which pattern of findings is expected in distal (type 1) renal tubular acidosis?

  1. Metabolic alkalosis with hypokalemia
  2. Urine pH below 5.0 with hyperkalemia
  3. Urine pH above 5.5 with hypokalemia Correct answer.
  4. Proximal bicarbonate wasting with Fanconi syndrome

Explanation

Distal RTA results from impaired hydrogen ion secretion by alpha-intercalated cells, so the urine cannot be maximally acidified and pH remains above 5.5 despite systemic acidosis. Sodium wasting and secondary hyperaldosteronism promote potassium loss, and the resulting hypocitraturia and hypercalciuria favor calcium phosphate stones.

Question 20Renal Anatomy, Physiology, and Pathophysiology

Which structure is the narrowest point of the ureter and the most common site of stone impaction?

  1. Mid-ureter
  2. Renal pelvis
  3. Ureterovesical junction Correct answer.
  4. Crossing of the iliac vessels

Explanation

The ureter has three anatomic constrictions: the ureteropelvic junction, the crossing of the iliac vessels at the pelvic brim, and the ureterovesical junction. The ureterovesical junction is the narrowest of the three, which is why calculi most often lodge there and produce referred pain to the groin.

Question 21Renal Anatomy, Physiology, and Pathophysiology

Clearance of para-aminohippurate is used to estimate renal plasma flow. Which circumstance would cause this estimate to underestimate true renal plasma flow?

  1. Active secretion of PAH by the proximal tubule
  2. Filtration of PAH at the glomerulus
  3. A urine flow rate above 2 mL/min
  4. Incomplete extraction of PAH during a single pass Correct answer.

Explanation

The PAH method assumes that nearly all PAH reaching the kidney is removed in one pass, so clearance equals effective renal plasma flow. If extraction falls short of about 90%, more PAH leaves in the renal vein and clearance underestimates true plasma flow.

Question 22Renal Anatomy, Physiology, and Pathophysiology

In a patient with SIADH whose urine osmolality exceeds plasma osmolality, the free water clearance (CH2O = V - Cosm) is best described as which of the following?

  1. Increasing as urine osmolality falls
  2. Zero
  3. Negative Correct answer.
  4. Positive and equal to the osmolar clearance

Explanation

Free water clearance is urine flow minus osmolar clearance; when the urine is more concentrated than plasma, the osmolar clearance exceeds the urine flow and CH2O becomes negative. Negative free water clearance means the kidney is returning free water to the body, which dilutes the serum sodium in SIADH.

Question 23Renal Anatomy, Physiology, and Pathophysiology

Glomerulotubular balance refers to which phenomenon?

  1. Proportional reabsorption of filtered sodium in the proximal tubule Correct answer.
  2. Adjustment of distal sodium delivery by the macula densa
  3. Constancy of renal blood flow across changes in arterial pressure
  4. Reflex constriction of the afferent arteriole when systemic pressure rises

Explanation

Glomerulotubular balance is the intrinsic ability of the proximal tubule to reabsorb a nearly constant fraction, about 65%, of the filtered sodium and water as GFR varies. This protects the distal nephron from swings in delivered load and is largely mediated by changes in peritubular oncotic forces and brush border transporter density.

Question 24Renal Anatomy, Physiology, and Pathophysiology

A young man presents with microscopic hematuria, progressive renal impairment, sensorineural hearing loss, and anterior lenticonus. Which protein is most likely defective?

  1. Type I collagen
  2. Podocin
  3. Fibrocystin
  4. Type IV collagen Correct answer.

Explanation

Alport syndrome results from mutations in type IV collagen, most often the X-linked COL4A5 gene, producing a defective glomerular basement membrane with characteristic basket-weave splitting on electron microscopy. Type IV collagen is also expressed in the cochlea and lens capsule, which explains the hearing loss and anterior lenticonus.

Question 25Renal Anatomy, Physiology, and Pathophysiology

A 40-year-old presents with hypertension, flank pain, and bilaterally enlarged kidneys containing multiple cysts. Which genetic abnormality most commonly underlies this condition?

  1. PKD1 on chromosome 16 Correct answer.
  2. COL4A5 on the X chromosome
  3. PKD2 on chromosome 16
  4. PKHD1 on chromosome 8

Explanation

Autosomal dominant polycystic kidney disease is caused in about 85% of cases by mutations in PKD1 on chromosome 16, which encodes polycystin-1. PKD2 mutations account for most remaining cases and typically produce milder, later-onset disease.

Question 26Renal Anatomy, Physiology, and Pathophysiology

Which protein forms the core of the glomerular slit diaphragm between podocyte foot processes?

  1. Aquaporin-1
  2. Nephrin Correct answer.
  3. Type IV collagen
  4. Fibronectin

Explanation

The slit diaphragm is a specialized cell-cell junction between podocyte foot processes, and nephrin is its main structural protein. Loss of nephrin disrupts size selectivity and causes proteinuria. Type IV collagen is a basement membrane component rather than the slit diaphragm.

Question 27Renal Anatomy, Physiology, and Pathophysiology

Which nephron segment is virtually impermeable to water while actively reabsorbing NaCl?

  1. Thick ascending limb of the loop of Henle Correct answer.
  2. Medullary collecting duct
  3. Descending thin limb of the loop of Henle
  4. Proximal convoluted tubule

Explanation

The thick ascending limb actively transports NaCl through NKCC2 but has very low water permeability because it lacks aquaporins in its apical and basolateral membranes. Water therefore cannot follow osmotically, which dilutes the tubular fluid and helps establish the medullary osmotic gradient.

Question 28Renal Anatomy, Physiology, and Pathophysiology

At the renal hilum, which structure lies most posteriorly?

  1. Sympathetic nerve fibers
  2. Renal artery
  3. Renal vein
  4. Renal pelvis Correct answer.

Explanation

At the renal hilum the renal vein is most anterior, the renal artery is intermediate, and the renal pelvis is most posterior. This relationship is used when placing vascular clamps during nephrectomy.

Question 29Renal Anatomy, Physiology, and Pathophysiology

Acetazolamide increases urinary bicarbonate loss by inhibiting which proximal tubule target?

  1. Apical sodium-glucose cotransport
  2. The NHE3 sodium/hydrogen exchanger
  3. Brush-border carbonic anhydrase Correct answer.
  4. Basolateral Na+/K+-ATPase

Explanation

Acetazolamide inhibits carbonic anhydrase in the proximal tubule brush border and cytoplasm, reducing the conversion of CO2 and water to carbonic acid and thereby reducing bicarbonate reabsorption. The result is a bicarbonate-rich diuresis. It does not directly inhibit Na+/K+-ATPase, SGLT2, or NHE3.

Question 30Renal Anatomy, Physiology, and Pathophysiology

The vasa recta preserve the medullary osmotic gradient primarily through which mechanism?

  1. Osmotic diuresis in the collecting duct
  2. Active sodium secretion into the descending limb
  3. Pressure natriuresis in the papilla
  4. Countercurrent exchange with hairpin capillary loops Correct answer.

Explanation

Vasa recta are hairpin capillaries that run alongside the loops of Henle, and countercurrent exchange allows them to remove water and solutes without washing out the medullary gradient. Active sodium secretion and pressure natriuresis do not describe this vascular process.

Question 31Renal Anatomy, Physiology, and Pathophysiology

Hydrogen ion secretion by the collecting duct is carried out mainly by which cell type?

  1. Mesangial cells
  2. Juxtaglomerular cells
  3. Type A intercalated cells Correct answer.
  4. Principal cells

Explanation

Type A intercalated cells possess apical H+-ATPase and basolateral Cl-/HCO3- exchangers, and they secrete hydrogen ions during acidosis. Principal cells reabsorb sodium and secrete potassium rather than hydrogen ions.

Question 32Renal Anatomy, Physiology, and Pathophysiology

A chronic rise in arterial pressure produces a sustained increase in sodium excretion through which renal response?

  1. Reduced medullary blood flow
  2. Increased renin release
  3. Enhanced proximal sodium reabsorption
  4. Pressure natriuresis Correct answer.

Explanation

Pressure natriuresis is the phenomenon in which increased renal perfusion pressure reduces tubular sodium reabsorption and increases sodium excretion. It is mediated by changes in peritubular hydrostatic and oncotic pressures and by reduced sympathetic tone. Increased renin release would instead promote sodium retention.

Question 33Renal Anatomy, Physiology, and Pathophysiology

A dehydrated patient has BUN 40 mg/dL, creatinine 1.0 mg/dL, urine sodium 10 mEq/L, and FENa 0.6%. Which condition best fits?

  1. Acute interstitial nephritis
  2. Acute tubular necrosis
  3. Prerenal azotemia Correct answer.
  4. Obstructive uropathy

Explanation

A BUN-to-creatinine ratio above 20 with low urine sodium and FENa below 1% indicates intact tubular sodium avidity, characteristic of prerenal azotemia. In acute tubular necrosis, FENa typically exceeds 2% because damaged tubules cannot reabsorb sodium.

Question 34Renal Anatomy, Physiology, and Pathophysiology

A 55-year-old with nephrotic syndrome undergoes biopsy showing thickened glomerular basement membrane with subepithelial deposits and spike-like projections. What is the most likely diagnosis?

  1. Membranous nephropathy Correct answer.
  2. Focal segmental glomerulosclerosis
  3. IgA nephropathy
  4. Minimal change disease

Explanation

Membranous nephropathy produces subepithelial immune deposits and a thickened basement membrane with silver-stain spikes. Minimal change disease shows normal light microscopy, and IgA nephropathy shows mesangial deposits.

Question 35Renal Anatomy, Physiology, and Pathophysiology

Staghorn calculi composed of magnesium ammonium phosphate are most closely associated with infection by which organism?

  1. Candida albicans
  2. Escherichia coli
  3. Proteus mirabilis Correct answer.
  4. Staphylococcus saprophyticus

Explanation

Proteus mirabilis produces urease, which splits urea into ammonia and raises urine pH; this favors precipitation of magnesium ammonium phosphate (struvite) stones. Escherichia coli and Staphylococcus saprophyticus do not typically produce urease.

Question 36Renal Anatomy, Physiology, and Pathophysiology

A 62-year-old man has painless hematuria, a left-sided varicocele that does not decompress when supine, and a renal mass. Which tumor is most likely?

  1. Wilms tumor
  2. Renal oncocytoma
  3. Renal cell carcinoma Correct answer.
  4. Transitional cell carcinoma of the renal pelvis

Explanation

Renal cell carcinoma can invade the left renal vein and obstruct the left testicular vein, producing a varicocele that fails to empty when supine. Transitional cell carcinoma arises in the urothelium and does not typically cause varicocele.

Question 37Renal Anatomy, Physiology, and Pathophysiology

If efferent arteriolar resistance rises while afferent resistance and systemic pressure remain constant, what is the expected effect on glomerular filtration rate and renal plasma flow?

  1. Both GFR and renal plasma flow increase
  2. GFR increases; renal plasma flow decreases Correct answer.
  3. GFR decreases; renal plasma flow increases
  4. Both GFR and renal plasma flow decrease

Explanation

Afferent and efferent arteriolar tone determine glomerular capillary pressure. Selective efferent constriction raises glomerular pressure and filtration fraction, so GFR rises, while the increased resistance reduces renal plasma flow. Afferent constriction would lower both.

Question 38Renal Anatomy, Physiology, and Pathophysiology

In the inner medulla, urea recycling between the collecting duct and the loop of Henle depends most directly on which transporter?

  1. NHE3 in the proximal tubule
  2. UT-A urea transporters in the collecting duct Correct answer.
  3. ENaC in the collecting duct
  4. NKCC2 in the thick ascending limb

Explanation

UT-A transporters in the inner medullary collecting duct allow urea to diffuse into the medullary interstitium, where it is trapped and recycled. NKCC2 and ENaC transport sodium and chloride rather than urea.

Question 39Renal Anatomy, Physiology, and Pathophysiology

During chronic metabolic acidosis, the proximal tubule increases ammonium excretion primarily by which adaptation?

  1. Increasing glutamine metabolism and ammoniagenesis Correct answer.
  2. Suppressing apical NHE3 activity
  3. Decreasing phosphate-dependent glutaminase activity
  4. Reducing glutamine uptake from the blood

Explanation

Chronic acidosis induces phosphate-dependent glutaminase and glutamine uptake, increasing ammoniagenesis and ammonium excretion. This adaptation enhances net acid excretion and helps restore plasma bicarbonate. Suppressing NHE3 would reduce acid secretion rather than increase it.

Question 40Renal Anatomy, Physiology, and Pathophysiology

The glomerular filtrate is nearly free of albumin even though albumin is abundant in plasma. Which factor best explains this?

  1. Fixed negative charges within the filtration barrier repel anionic albumin Correct answer.
  2. High plasma oncotic pressure keeps albumin within the glomerular capillaries
  3. Podocytes actively endocytose albumin from the urinary space
  4. Endothelial fenestrations are too small to permit albumin to pass

Explanation

The glomerular filtration barrier restricts macromolecules by both size and charge. The heparan-sulfate-rich basement membrane and the sialylated glycocalyx of podocytes carry fixed negative charges that electrostatically hinder filtration of anionic albumin, with size selectivity adding further restriction. The small quantity of albumin that does enter the filtrate is normally reclaimed by proximal tubule endocytosis rather than by podocytes.

Question 41Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

A patient's eGFR has been 50 mL/min/1.73 m² on two measurements six months apart. Which KDIGO GFR category does this represent?

  1. G2
  2. G3b
  3. G3a Correct answer.
  4. G4

Explanation

KDIGO categorizes GFR as G1 (≥90), G2 (60–89), G3a (45–59), G3b (30–44), G4 (15–29), and G5 (<15 mL/min/1.73 m²). An eGFR of 50 falls in the G3a band, and chronicity is established because the value has persisted beyond 3 months.

Question 42Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

In an adult, oliguria is best defined as a 24-hour urine output of less than:

  1. 2,000 mL
  2. 100 mL
  3. 400 mL Correct answer.
  4. 1,000 mL

Explanation

Oliguria is conventionally defined as urine output below 400 mL per 24 hours (roughly 0.5 mL/kg/h in many adults). Output below about 100 mL per 24 hours is termed anuria, and output above the oliguric threshold is described as nonoliguric.

Question 43Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

Which test is preferred for detecting albuminuria in a patient with chronic kidney disease?

  1. Urine albumin-to-creatinine ratio Correct answer.
  2. Random dipstick protein
  3. 24-hour urine total protein
  4. Urine specific gravity

Explanation

A spot urine albumin-to-creatinine ratio corrects for hydration and detects albumin at low levels, which makes it the preferred screening and monitoring test. Standard dipstick protein is insensitive to modest albumin loss, and a 24-hour collection is cumbersome and prone to collection error.

Question 44Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

Which ECG change is most characteristic of hyperkalemia?

  1. Prominent U waves
  2. Peaked and narrowed T waves Correct answer.
  3. Atrial fibrillation with rapid ventricular response
  4. Prolonged QT interval

Explanation

Hyperkalemia initially produces tall, peaked, narrow-based T waves, and with worsening levels can progress to widened QRS complexes, loss of P waves, and sine-wave patterns. This progression reflects delayed ventricular conduction as extracellular potassium rises.

Question 45Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

A patient with acute kidney injury and a history of recurrent kidney stones has a rising creatinine. Which imaging study is most appropriate to exclude obstruction?

  1. Renal ultrasound Correct answer.
  2. CT with intravenous contrast
  3. MRI with gadolinium
  4. Magnetic resonance angiography

Explanation

Ultrasonography is noninvasive, avoids nephrotoxic contrast and gadolinium exposure, and reliably shows hydronephrosis when obstruction is present. Contrast-enhanced CT and gadolinium-based studies carry risk in a patient with impaired kidney function.

Question 46Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

To lower serum phosphate in a patient with chronic kidney disease, calcium acetate should be administered:

  1. With meals Correct answer.
  2. One hour before meals on an empty stomach
  3. Once daily at bedtime
  4. Only when phosphate exceeds 6 mg/dL

Explanation

Calcium acetate is a phosphate binder that must be present in the gut lumen with food to bind dietary phosphate and limit absorption. Dosing away from meals provides little phosphate-binding effect.

Question 47Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

Which urinalysis finding suggests that hematuria originates in the glomerulus rather than the lower urinary tract?

  1. Alkaline urine pH
  2. Red blood cell casts Correct answer.
  3. Triple phosphate crystals
  4. Isomorphic red blood cells

Explanation

Red blood cells that enter the tubular lumen from the glomerulus become entrapped in Tamm-Horsfall mucoprotein, forming casts that are a marker of glomerular bleeding. Isomorphic cells without casts are more typical of a lower tract source.

Question 48Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

A patient has a left forearm arteriovenous fistula. Where should blood pressure be measured?

  1. On the left arm, below the fistula
  2. On either arm, whichever is more convenient
  3. On the arm without the fistula Correct answer.
  4. On the left arm only when the fistula is not in use

Explanation

Cuff inflation over an access arm can compress the fistula or graft, risking thrombosis and loss of the access. Blood pressure is therefore measured on the arm contralateral to the vascular access.

Question 49Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

A patient with vomiting and poor oral intake has a BUN of 42 mg/dL and a creatinine of 1.4 mg/dL. What does the BUN-to-creatinine ratio suggest?

  1. An intrinsic renal process
  2. A laboratory error, since BUN and creatinine rise together
  3. A prerenal cause of the elevated BUN Correct answer.
  4. A postrenal cause

Explanation

A BUN-to-creatinine ratio above roughly 20:1 suggests prerenal azotemia, because volume depletion increases proximal urea reabsorption while creatinine handling is largely unchanged. Intrinsic and postrenal processes more often produce a ratio near 10–15:1.

Question 50Assessment, Diagnosis, and Monitoring of the Patient with Kidney Disease

A patient with oliguric acute kidney injury who is not receiving diuretics has a fractional excretion of sodium of 0.4%. Which interpretation fits best?

  1. Prerenal azotemia with sodium avidity Correct answer.
  2. Acute tubular necrosis with tubular injury
  3. Acute interstitial nephritis
  4. Obstructive uropathy

Explanation

A fractional excretion of sodium below 1% indicates that the tubules are reabsorbing sodium avidly, which is the expected response to decreased renal perfusion. Values above 1–2% suggest tubular injury or another cause of salt wasting.