Units of measurement

14 Kerala PSC Lab Technician Gr II practice questions on Units of measurement, part of Biochemistry. The first 14 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 · Easy

   The SI unit of enzyme (catalytic) activity is the:

   1. AKatal
   2. BPascal second
   3. CMole per litre
   4. DInternational unit (U)

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   Answer: A · Katal

   One katal is the amount of enzyme that converts 1 mole of substrate per second. The international unit (U), still used by most laboratories, converts 1 µmol per minute, so 1 U = 16.67 nkat. Enzyme results are therefore reported as U/L or, in SI form, µkat/L. Mole per litre is the SI unit of concentration, not of activity.

   • B: Pascal second is the SI unit of viscosity.
   • C: Mole per litre measures concentration.
   • D: The international unit (µmol/min) is a non-SI unit, although widely used.

2. Question 2 · Hard

   A Kerala laboratory reports blood urea as 45 mg/dL. A hospital abroad asks for urea in mmol/L (urea molar mass 60 g/mol). What value should be sent?

   1. A0.75 mmol/L
   2. B75 mmol/L
   3. C7.5 mmol/L
   4. D16.1 mmol/L

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   Answer: C · 7.5 mmol/L

   45 mg/dL is 450 mg/L, and 450 ÷ 60 = 7.5 mmol/L. The trap is to treat the result as blood urea nitrogen (BUN) and use the BUN factor of 0.357, which gives 16.1 mmol/L. Urea contains two nitrogen atoms (28 of its 60 g/mol), so urea in mg/dL = BUN in mg/dL × 2.14. Always check whether a report gives urea or urea nitrogen before converting.

   • A: 0.75 mmol/L leaves out the decilitre-to-litre step.
   • B: 75 mmol/L multiplies by 100 instead of 10 in the decilitre-to-litre step.
   • D: 16.1 mmol/L treats the urea result as BUN.

3. Question 3 · Medium

   A serum creatinine of 2.0 mg/dL is to be reported in SI units. With a molar mass of 113 g/mol, what is the result?

   1. A1,770 µmol/L
   2. B226 µmol/L
   3. C177 µmol/L
   4. D17.7 µmol/L

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   Answer: C · 177 µmol/L

   2.0 mg/dL is 20 mg/L. Dividing by the molar mass gives 20 ÷ 113 = 0.177 mmol/L, which is 177 µmol/L. The shortcut factor is 88.4: mg/dL × 88.4 = µmol/L. The usual mistakes are getting the decilitre-to-litre step wrong, or multiplying by the molar mass instead of dividing.

   • A: 1,770 µmol/L treats a decilitre as one hundredth of a litre.
   • B: 226 comes from multiplying by the molar mass instead of dividing.
   • D: 17.7 µmol/L leaves out the decilitre-to-litre step.

4. Question 4 · Easy

   The angstrom, a non-SI unit of wavelength found in older texts, is equal to:

   1. A0.01 nm
   2. B0.1 nm
   3. C10 nm
   4. D1 nm

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   Answer: B · 0.1 nm

   One angstrom (Å) is 10^-10 m, which is 0.1 nanometre. Wavelengths are now given in nanometres, so a 5400 Å filter is a 540 nm filter. The millimicron (mµ) of older texts is the same as the nanometre. The micron (µ) is the micrometre, 1000 nm.

   • A: 0.01 nm equals 0.1 Å.
   • C: 10 nm equals 100 Å.
   • D: 1 nm equals 10 Å.

5. Question 5 · Medium

   Serum calcium is 10 mg/dL (atomic weight 40, valency 2). Expressed in mEq/L, this is:

   1. A0.5 mEq/L
   2. B2.5 mEq/L
   3. C5.0 mEq/L
   4. D1.25 mEq/L

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   Answer: C · 5.0 mEq/L

   10 mg/dL is 100 mg/L, and 100 ÷ 40 = 2.5 mmol/L. Milliequivalents = millimoles × valency, so 2.5 × 2 = 5.0 mEq/L. Equivalents count charge, so for a divalent ion the mEq/L figure is twice the mmol/L figure. For a monovalent ion such as sodium, mmol/L and mEq/L are the same number.

   • A: 0.5 leaves out the decilitre-to-litre step (10 ÷ 20).
   • B: 2.5 is the result in mmol/L, before multiplying by the valency.
   • D: 1.25 divides by the valency instead of multiplying.

6. Question 6 · Medium

   A patient's total leukocyte count of 8,000 cells/µL (cells/mm³) is expressed in SI units as:

   1. A8.0 × 10¹²/L
   2. B8.0 × 10³/L
   3. C8.0 × 10⁹/L
   4. D8.0 × 10⁶/L

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7. Question 7 · Easy

   What is the SI base unit for amount of substance?

   1. AEquivalent
   2. BOsmole
   3. CMole
   4. DGram

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8. Question 8 · Medium

   A patient's fasting plasma glucose is 126 mg/dL. In SI units (glucose molar mass 180 g/mol), this is:

   1. A0.7 mmol/L
   2. B70 mmol/L
   3. C7.0 mmol/L
   4. D22.7 mmol/L

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9. Question 9 · Easy

   Mean cell volume is reported in femtolitres. One femtolitre equals:

   1. A10⁻¹⁸ L
   2. B10⁻¹⁵ L
   3. C10⁻⁹ L
   4. D10⁻¹² L

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10. Question 10 · Hard

    An ALT activity of 60 U/L (1 U converts 1 µmol of substrate per minute) is to be reported in SI units. The result is:

    1. A3600 µkat/L
    2. B60 µkat/L
    3. C1.0 µkat/L
    4. D0.06 µkat/L

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11. Question 11 · Medium

    A serum total cholesterol of 200 mg/dL (molar mass 386.6 g/mol) is reported in SI units as about:

    1. A5.2 mmol/L
    2. B0.52 mmol/L
    3. C52 mmol/L
    4. D7.7 mmol/L

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12. Question 12 · Easy

    A hemoglobin of 12 g/dL is reported in SI units as:

    1. A1.2 g/L
    2. B12 g/L
    3. C120 g/L
    4. D1,200 g/L

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13. Question 13 · Hard

    A report from abroad gives a jaundiced patient's total bilirubin as 85.5 µmol/L. Bilirubin molar mass is 584.7 g/mol. What is the value in mg/dL?

    1. A50 mg/dL
    2. B5.0 mg/dL
    3. C1.5 mg/dL
    4. D0.5 mg/dL

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14. Question 14 · Easy

    Mean cell hemoglobin is reported in picograms. One picogram is:

    1. A10⁻¹² g
    2. B10⁻¹⁵ g
    3. C10⁻⁶ g
    4. D10⁻⁹ g

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