Urine chemistry, clearance tests, CSF and body fluids

47 Kerala PSC Lab Technician Gr II practice questions on Urine chemistry, clearance tests, CSF and body fluids, part of Biochemistry. The first 25 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 45-year-old man collects a 24-hour urine of 2,160 mL with urine creatinine 90 mg/dL. Serum creatinine is 1.5 mg/dL. His creatinine clearance, not corrected for body surface area, is:

   1. A90 mL/min
   2. B60 mL/min
   3. C2,160 mL/min
   4. D135 mL/min

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   Answer: A · 90 mL/min

   First convert the volume to a flow rate: 2,160 mL ÷ 1,440 min = 1.5 mL/min. Clearance = U × V ÷ P = 90 × 1.5 ÷ 1.5 = 90 mL/min. Leaving out V gives 60, leaving out P gives 135, and dividing the volume by 60 instead of 1,440 gives 2,160. The commonest error in practice is an incomplete collection, which is checked from the total creatinine excreted per day.

   • B: 60 mL/min is U ÷ P alone, leaving out the urine flow.
   • C: 2,160 mL/min comes from dividing the volume by 60 minutes instead of 1,440.
   • D: 135 mL/min is U × V without dividing by the serum creatinine.

2. Question 2 · Easy

   The lecithin/sphingomyelin (L/S) ratio in amniotic fluid is used to assess fetal:

   1. ANeural tube defects
   2. BLung maturity
   3. CKidney maturity
   4. DHemolytic disease

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   Answer: B · Lung maturity

   Lecithin is the main surfactant made by the fetal lungs, and it rises sharply in the last weeks of pregnancy while sphingomyelin stays about the same. A ratio of 2.0 or more indicates mature lungs, and a lower ratio warns of respiratory distress syndrome after birth. The ratio is measured by thin-layer chromatography. Neural tube defects are assessed with amniotic fluid AFP, and hemolytic disease with amniotic fluid bilirubin.

   • A: Neural tube defects are assessed by AFP and acetylcholinesterase.
   • C: Amniotic fluid creatinine, not the L/S ratio, was used for kidney maturity.
   • D: Hemolytic disease is assessed by amniotic fluid bilirubin at 450 nm.

3. Question 3 · Medium

   Urea clearance is lower than the glomerular filtration rate because urea is:

   1. AActively secreted by the tubules
   2. BNot filtered by the glomeruli
   3. CTightly bound to plasma proteins
   4. DPartly reabsorbed by the tubules

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   Answer: D · Partly reabsorbed by the tubules

   Urea is freely filtered, but about 40-50% of it diffuses back from the tubules with water, more so when urine flow is low. Van Slyke therefore used the maximum clearance (UV/P) when urine flow is above 2 mL/min and the standard clearance (U√V/P) below it. Normal values are about 75 and 54 mL/min respectively. Because it depends on hydration, urea clearance has been replaced by creatinine clearance for GFR.

   • A: Secretion would make the clearance higher than the GFR.
   • B: Urea passes freely through the glomerular filter.
   • C: Urea is a small molecule that is not bound to plasma proteins.

4. Question 4 · Medium

   Maternal urinary estriol reflects fetal well-being because its synthesis needs the:

   1. AFetal adrenal, fetal liver and placenta
   2. BMaternal adrenal cortex alone
   3. CMaternal ovary and corpus luteum
   4. DPlacenta alone, from maternal cholesterol

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   Answer: A · Fetal adrenal, fetal liver and placenta

   The fetal adrenal makes DHEA sulfate, the fetal liver adds a 16-hydroxyl group, and the placenta converts this to estriol. Estriol enters the mother's blood and is excreted in her urine as conjugates. Because the fetus and the placenta both take part, a falling estriol in late pregnancy suggests fetal compromise. Unconjugated estriol is also part of the second-trimester screen for Down syndrome, where it is low.

   • B: The maternal adrenal contributes little estriol in pregnancy.
   • C: The corpus luteum supplies hormones only in early pregnancy.
   • D: The placenta cannot make estrogens from cholesterol without fetal precursors.

5. Question 5 · Easy

   Urine that turns black on standing, especially when made alkaline, suggests which disorder?

   1. ACystinuria
   2. BPhenylketonuria
   3. CAcute intermittent porphyria
   4. DAlkaptonuria

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   Answer: D · Alkaptonuria

   Alkaptonuria is a deficiency of homogentisate oxidase in the breakdown of tyrosine. Homogentisic acid is excreted in the urine and oxidizes in air, faster in alkaline urine, to a black pigment. The urine also reduces Benedict's reagent. In adults the pigment deposits in cartilage (ochronosis) and causes arthritis.

   • A: Cystinuria causes stones and hexagonal crystals, not dark urine.
   • B: Phenylketonuria urine has a mousy odor but does not turn black.
   • C: Porphyria urine darkens to a red or port-wine color.

6. Question 6 · Medium

   A 7-month-old fair-skinned child has delayed milestones and a musty (mousy) body odor. Urine turns green with 10% ferric chloride. The most likely disorder is:

   1. AMaple syrup urine disease
   2. BTyrosinemia
   3. CPhenylketonuria
   4. DAlkaptonuria

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7. Question 7 · Medium

   Inulin clearance is the reference method for measuring GFR because inulin is:

   1. ACompletely reabsorbed by the tubules
   2. BFreely filtered, not reabsorbed or secreted
   3. CSecreted by the tubules at a fixed rate
   4. DProduced by muscle at a steady rate

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8. Question 8 · Easy

   A 55-year-old man has episodes of facial flushing, watery diarrhea and wheezing. Which 24-hour urine test is most useful?

   1. A5-Hydroxyindoleacetic acid (5-HIAA)
   2. BHomovanillic acid (HVA)
   3. C17-Ketosteroids
   4. DVanillylmandelic acid (VMA)

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9. Question 9 · Easy

   Vanillylmandelic acid (VMA) in urine is the main end product of:

   1. ADopamine and L-dopa
   2. BAdrenaline and noradrenaline
   3. CSerotonin and tryptophan
   4. DCortisol and cortisone

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10. Question 10 · Hard

    A 50-year-old man with alcoholic cirrhosis has ascites. Serum albumin is 2.9 g/dL and ascitic fluid albumin, taken the same day, is 1.1 g/dL. What is the serum-ascites albumin gradient (cut-off 1.1 g/dL), and what does it indicate?

    1. A4.0 g/dL, portal hypertension
    2. B1.8 g/dL, peritoneal TB or cancer
    3. C0.4 g/dL, peritoneal TB or cancer
    4. D1.8 g/dL, portal hypertension

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11. Question 11 · Medium

    A 40-year-old man has a lymphocyte-rich pericardial effusion with high adenosine deaminase (ADA) activity. The most likely cause is:

    1. AHypothyroid effusion
    2. BUremic pericarditis
    3. CTuberculous pericarditis
    4. DViral pericarditis

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12. Question 12 · Easy

    What mainly gives normal urine its yellow colour?

    1. AUrochrome
    2. BBiliverdin
    3. CUroerythrin
    4. DBilirubin

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13. Question 13 · Easy

    In a healthy adult, CSF glucose is about what percentage of the plasma glucose?

    1. A20-30%
    2. B60-70%
    3. C95-100%
    4. D130-150%

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14. Question 14 · Hard

    A 10-day-old baby (karyotype 46,XX) has ambiguous genitalia, vomiting and poor weight gain. Serum sodium is 124 mEq/L and potassium 7.0 mEq/L. Urinary 17-ketosteroids and pregnanetriol are both raised. The most likely diagnosis is:

    1. ACongenital adrenal hypoplasia
    2. B11-Beta-hydroxylase deficiency
    3. C17-Alpha-hydroxylase deficiency
    4. D21-Hydroxylase deficiency

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15. Question 15 · Hard

    In a urea clearance test, blood urea is 30 mg/dL, urine urea 900 mg/dL and urine flow 1.44 mL/min. The flow is below the augmentation limit of 2 mL/min, so standard clearance applies. What is the standard urea clearance?

    1. A36 mL/min
    2. B43 mL/min
    3. C30 mL/min
    4. D25 mL/min

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16. Question 16 · Easy

    Which substance is the main nitrogenous constituent of normal urine?

    1. AAmmonia
    2. BUrea
    3. CUric acid
    4. DCreatinine

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17. Question 17 · Easy

    Total urinary protein excretion in a healthy adult is normally less than:

    1. A30 mg/day
    2. B150 mg/day
    3. C1.5 g/day
    4. D3.5 g/day

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18. Question 18 · Medium

    When urine containing Bence Jones protein is heated slowly, the protein:

    1. AStays in solution at every temperature
    2. BPrecipitates at 40-60 °C and dissolves near 100 °C
    3. CPrecipitates on boiling and stays insoluble on cooling
    4. DPrecipitates only after cooling to 4 °C

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19. Question 19 · Medium

    A 30-year-old man has weakness rising from the legs. His CSF shows protein 190 mg/dL (reference 15-45 mg/dL), 3 cells/µL and normal glucose. This finding is typical of:

    1. AGuillain-Barré syndrome
    2. BViral meningitis
    3. CTuberculous meningitis
    4. DAcute bacterial meningitis

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20. Question 20 · Medium

    At 16 weeks of pregnancy, amniotic fluid shows a raised alpha-fetoprotein and an acetylcholinesterase band on gel electrophoresis. These findings point to:

    1. ADown syndrome
    2. BOpen neural tube defect
    3. CFetal lung immaturity
    4. DRh hemolytic disease

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21. Question 21 · Medium

    An infant's urine has a burnt-sugar odour and forms a yellow precipitate with 2,4-dinitrophenylhydrazine. Which disorder is most likely?

    1. AGalactosemia
    2. BCystinuria
    3. CAlkaptonuria
    4. DMaple syrup urine disease

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22. Question 22 · Medium

    Creatinine clearance slightly overestimates the true GFR because creatinine is:

    1. ABound to plasma proteins
    2. BAlso secreted by the tubules
    3. CMade in the kidney
    4. DPartly reabsorbed by the tubules

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23. Question 23 · Hard

    A 28-year-old man's routine urine shows glucose 1+ on two occasions. His fasting plasma glucose is 84 mg/dL, the 2-hour glucose after 75 g is 118 mg/dL and HbA1c is 5.1%. Other urine findings and kidney function are normal. The most likely explanation is:

    1. ARenal glycosuria
    2. BImpaired glucose tolerance
    3. CContamination with detergent
    4. DDiabetes mellitus

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24. Question 24 · Medium

    In a Rh-immunised pregnancy, the amniotic fluid absorbance at 450 nm (ΔOD450) is measured to assess the:

    1. ARisk of neural tube defect
    2. BFetal lung maturity
    3. CSeverity of fetal hemolysis
    4. DFetal renal function

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25. Question 25 · Easy

    Esbach's albuminometer for estimating urinary protein uses a reagent containing:

    1. ASulphosalicylic acid
    2. BPicric acid
    3. CTrichloroacetic acid
    4. DNitric acid

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