Renal and metabolic disease correlation

15 DOH Abu Dhabi (HAAD) lab licensing practice questions on Renal and metabolic disease correlation, part of Urinalysis and Body Fluids. The first 15 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 47-year-old man has taken tenofovir disoproxil fumarate for chronic hepatitis B for 5 years; he does not have diabetes. Results: plasma glucose 5.1 mmol/L (92 mg/dL); serum phosphate 0.52 mmol/L (1.6 mg/dL; reference 0.81-1.45 mmol/L); bicarbonate 17 mmol/L with a normal anion gap; uric acid 120 µmol/L (2.0 mg/dL; reference 200-420 µmol/L); creatinine 118 µmol/L (1.33 mg/dL). Urine: pH 5.2, glucose 2+, protein 1+; protein-to-creatinine ratio 90 mg/mmol (reference below 15) but albumin-to-creatinine ratio 5 mg/mmol (reference below 3); generalized aminoaciduria. The serum free light chain ratio is normal. The pattern is most consistent with:

   1. ALight chain overflow proteinuria
   2. BProximal tubular injury from tenofovir
   3. CDistal renal tubular acidosis
   4. DGlomerular injury with nephrotic proteinuria

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   Answer: B · Proximal tubular injury from tenofovir

   Glucose in the urine with a normal plasma glucose, low phosphate and urate from urinary losses, generalized aminoaciduria and a normal anion gap acidosis together show a general failure of proximal tubular reabsorption (Fanconi syndrome). Most of the urine protein is not albumin, since the protein-to-creatinine ratio is many times the albumin ratio; it is low-molecular-weight protein that the proximal tubule normally reclaims. Tenofovir disoproxil fumarate is a recognized cause of this proximal tubulopathy. Glomerular disease would give mainly albumin, and the normal free light chain ratio makes overflow proteinuria unlikely. A urine pH of 5.2 during acidosis shows that distal acidification works, which argues against distal renal tubular acidosis.

   • A: The serum free light chain ratio is normal, so light chains are not overflowing.
   • C: The urine pH of 5.2 during acidosis shows distal acid excretion is intact.
   • D: Glomerular proteinuria is mainly albumin, but albumin is only a small part of the protein here.

2. Question 2 · Hard

   A 12-year-old boy whose parents are first cousins is referred to a metabolic clinic in Abu Dhabi. He is tall and thin with long fingers, has learning difficulties and downward dislocation of both lenses, and had a deep vein thrombosis of the leg last year. His echocardiogram shows no aortic root dilatation. Urine: SG 1.018, pH 6.0, reagent strip negative for every analyte, no crystals seen. The cyanide-nitroprusside test gives a red-purple color, and the silver nitroprusside test is also positive. The most likely diagnosis is:

   1. ANephropathic cystinosis
   2. BClassical homocystinuria
   3. CMarfan syndrome
   4. DCystinuria

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   Answer: B · Classical homocystinuria

   The cyanide-nitroprusside test is positive with both cystine and homocystine, because cyanide reduces both disulfides to free sulfhydryl groups that react with nitroprusside. The silver nitroprusside test reduces homocystine but not cystine, so a positive result points to homocystinuria. Lens dislocation (typically downward), a tall marfanoid build, learning difficulty and venous thrombosis fit classical homocystinuria from cystathionine beta-synthase deficiency, an autosomal recessive disorder that is commoner with consanguinity. Cystinuria causes stones and hexagonal crystals with a negative silver nitroprusside test, Marfan syndrome leaves urine amino acids normal, and cystinosis causes Fanconi syndrome with glycosuria. A raised plasma total homocysteine confirms the diagnosis.

   • A: Cystinosis causes Fanconi syndrome, but the strip shows no glucose.
   • C: Marfan syndrome does not change urine amino acids, and its lenses usually dislocate upward.
   • D: Cystinuria gives stones and hexagonal crystals, and its silver nitroprusside test is negative.

3. Question 3 · Hard

   An infant's urine is negative for glucose on the reagent strip but positive for reducing substances by copper reduction (Clinitest). What does this suggest?

   1. AA non-glucose reducing sugar such as galactose
   2. BStrongly positive urine ketones
   3. CBilirubinuria from liver disease
   4. DHeavy proteinuria from nephrotic syndrome

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   Answer: A · A non-glucose reducing sugar such as galactose

   The reagent strip uses glucose oxidase, which reacts only with glucose. Copper reduction detects any reducing sugar, including galactose. In an infant, this pattern suggests galactosemia, which needs urgent confirmation, although newborn screening usually finds it first. High ascorbic acid can also cause this pattern, so the result must be interpreted clinically.

   • B: Ketones are not reducing sugars and are detected on a separate pad.
   • C: Bilirubin is not a reducing sugar.
   • D: Protein does not give a positive copper reduction test.

4. Question 4 · Medium

   Urine protein electrophoresis shows mainly beta-2 microglobulin and alpha-1 microglobulin, with little albumin. Which type of proteinuria does this show?

   1. AOverflow proteinuria from light chains
   2. BTubular proteinuria
   3. CSelective glomerular proteinuria
   4. DNonselective glomerular proteinuria

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   Answer: B · Tubular proteinuria

   Small proteins such as beta-2 microglobulin, alpha-1 microglobulin and retinol-binding protein pass the normal glomerulus freely and are almost all reabsorbed by the proximal tubule. When the tubules are damaged, for example by aminoglycosides, cadmium or Fanconi syndrome, these proteins appear in the urine while albumin stays low. Reagent strips, which detect mainly albumin, may read only negative or trace. Urine alpha-1 or beta-2 microglobulin can be measured to detect tubular injury.

   • A: Overflow proteinuria shows a single monoclonal light chain band.
   • C: Selective glomerular proteinuria is mainly albumin and transferrin.
   • D: Nonselective glomerular proteinuria has albumin plus large proteins such as IgG.

5. Question 5 · Hard

   A 22-year-old with sickle cell trait has painless visible hematuria. The red cells have normal shapes, there are no casts, and clotting tests are normal. After overnight water deprivation, urine osmolality is only 450 mOsm/kg (expected above 800). What best explains both findings?

   1. AHemolysis with free hemoglobin in the urine
   2. BImmune complex damage to the glomeruli
   3. CFailure of the pituitary to release vasopressin
   4. DSickling in the hypoxic, hypertonic renal medulla

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   Answer: D · Sickling in the hypoxic, hypertonic renal medulla

   The renal medulla has low oxygen tension, high osmolality and a low pH, conditions that make HbS polymerize even in people with sickle cell trait. Sickled cells block the vasa recta, damaging the papillae, which bleed, and destroying the countercurrent system, which limits urine concentration (hyposthenuria). The red cells keep a normal shape because the bleeding is not glomerular. Imaging is still needed, as renal medullary carcinoma is a rare cause of hematuria in sickle cell trait.

   • A: Hemoglobinuria gives a positive blood pad with few or no red cells.
   • B: Glomerular disease gives dysmorphic red cells and red cell casts.
   • C: Central diabetes insipidus would not explain the hematuria.

6. Question 6 · Medium

   Which urine screening test fits a suspected mucopolysaccharidosis, such as Hurler syndrome?

   1. ACyanide-nitroprusside test
   2. BCopper reduction test
   3. CFerric chloride test
   4. DGlycosaminoglycan screen

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7. Question 7 · Medium

   Urinalysis: protein 4+, blood negative, many oval fat bodies and fatty casts, a few hyaline casts and no red cell casts. Serum albumin is 18 g/L (1.8 g/dL; reference 35-50 g/L). This pattern best fits:

   1. AAcute glomerulonephritis
   2. BAcute pyelonephritis
   3. CAcute tubular necrosis
   4. DNephrotic syndrome

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8. Question 8 · Easy

   A newborn's urine and sweat have a musty, mousy odor. Which disorder does this suggest?

   1. APhenylketonuria
   2. BIsovaleric acidemia
   3. CAlkaptonuria
   4. DMaple syrup urine disease

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9. Question 9 · Hard

   A man on long-term lithium passes 5 L of urine a day; plasma glucose is normal. After water deprivation, urine osmolality is 160 mOsm/kg with plasma osmolality 302 mOsm/kg; after desmopressin it is 175 mOsm/kg. A normal response exceeds 600 mOsm/kg. The most likely cause is:

   1. AOsmotic diuresis
   2. BAVP deficiency (central diabetes insipidus)
   3. CPrimary polydipsia
   4. DAVP resistance (nephrogenic diabetes insipidus)

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10. Question 10 · Medium

    Which compound, found in urine or a newborn blood spot, is a specific marker of tyrosinemia type 1?

    1. APhenylpyruvic acid
    2. BSuccinylacetone
    3. CHomogentisic acid
    4. DAlloisoleucine

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11. Question 11 · Hard

    A woman with no flushing or diarrhea has a mildly raised 24-hour urine 5-HIAA. During the collection and the day before, she ate bananas, walnuts, pineapple and avocado every day. What is the best next step?

    1. AMeasure urine VMA instead of 5-HIAA
    2. BRepeat on a random urine with no diet change
    3. CRepeat after 3 days without serotonin-rich foods
    4. DReport it as evidence of a neuroendocrine tumor

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12. Question 12 · Hard

    A 9-year-old has a scaly red rash on sun-exposed skin and episodes of unsteady gait. Urine glucose and phosphate are normal, but neutral amino acids, including tryptophan, are greatly increased; cystine, lysine and arginine are normal, and plasma amino acids are normal to low. The most likely disorder is:

    1. ACystinuria
    2. BHartnup disease
    3. CPhenylketonuria
    4. DFanconi syndrome

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13. Question 13 · Easy

    Most urinary tract stones are made mainly of:

    1. ACalcium oxalate
    2. BUric acid
    3. CCystine
    4. DMagnesium ammonium phosphate

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14. Question 14 · Medium

    A child with Fanconi syndrome has a normal anion gap metabolic acidosis. Once plasma bicarbonate has fallen to 15 mmol/L, the urine pH is 5.2. Which defect explains the acidosis?

    1. AReduced bicarbonate reabsorption in the proximal tubule
    2. BOverproduction of organic acids by the tissues
    3. CLow aldosterone effect in the collecting duct
    4. DImpaired hydrogen ion secretion in the distal nephron

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15. Question 15 · Hard

    A 14-year-old boy has had microscopic hematuria with dysmorphic red cells for 3 years and now has protein 2+. He has high-frequency hearing loss, and his maternal uncle began dialysis at 32. C3 and C4 are normal. The most likely diagnosis is:

    1. AThin basement membrane nephropathy
    2. BIgA nephropathy
    3. CPost-streptococcal glomerulonephritis
    4. DAlport syndrome

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