Specimens: collection, anticoagulants and urine preservation

71 Kerala PSC Lab Technician Gr II practice questions on Specimens: collection, anticoagulants and urine preservation, 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 · Easy

   A blood sample for plasma ammonia should be:

   1. AKept at room temperature up to 4 hours
   2. BFrozen as whole blood until tested
   3. CKept on ice and tested within 30 minutes
   4. DKept at 37 °C and tested within 2 hours

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   Answer: C · Kept on ice and tested within 30 minutes

   Ammonia rises quickly in blood kept at room temperature, mainly from breakdown of glutamine and other nitrogenous compounds in the tube. The sample is drawn without prolonged tourniquet into EDTA or lithium heparin (never ammonium heparin), placed on ice, separated promptly and tested within about 30 minutes. Hemolysis also raises ammonia, because red cells contain more than plasma. Freezing whole blood would lyse the cells.

   • A: Ammonia rises significantly within an hour at room temperature.
   • B: Freezing whole blood lyses the cells and releases ammonia.
   • D: Warming speeds the release of ammonia in the tube.

2. Question 2 · Medium

   An alkaline phosphatase of 6 U/L (reference 40-130 U/L) is traced to a sample of EDTA plasma. Why is the result so low?

   1. AEDTA precipitates ALP along with calcium
   2. BEDTA removes the zinc and magnesium ALP needs
   3. CEDTA shifts the reaction pH out of range
   4. DEDTA lyses red cells and dilutes the plasma

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   Answer: B · EDTA removes the zinc and magnesium ALP needs

   Alkaline phosphatase is a zinc-containing enzyme that also needs magnesium as an activator. EDTA chelates these divalent ions, so ALP activity falls, often to very low values. For the same reason EDTA plasma is unsuitable for calcium and magnesium. ALP is measured on serum or heparinized plasma.

   • A: EDTA holds calcium in a soluble chelate; it does not precipitate the enzyme.
   • C: The assay buffer controls the pH; EDTA does not shift it out of range.
   • D: EDTA does not lyse red cells, and dilution would not cause such a fall.

3. Question 3 · Easy

   Under the Bio-Medical Waste Management Rules 2016, broken glass test tubes contaminated with blood are discarded in a:

   1. ACardboard box with blue marking
   2. BWhite translucent sharps container
   3. CYellow plastic bag
   4. DRed plastic bag

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   Answer: A · Cardboard box with blue marking

   The 2016 Rules place broken or discarded contaminated glassware, including vials and ampoules, in puncture-proof cardboard boxes with blue marking. The glass is disinfected, for example with sodium hypochlorite, or autoclaved and then sent for recycling. Needles, blades and other metal sharps go in the white translucent puncture-proof container, and contaminated recyclable plastics such as tubing and gloves in the red bag. Yellow bags take anatomical, soiled and pre-treated laboratory waste for incineration.

   • B: The white container is for needles, blades and other metal sharps.
   • C: Yellow bags are for anatomical, soiled and pre-treated laboratory waste.
   • D: Red bags are for contaminated recyclable plastics such as tubing and gloves.

4. Question 4 · Medium

   A ward sends heparinized blood for sodium and potassium. Which heparin salt is appropriate?

   1. APotassium heparin
   2. BLithium heparin
   3. CAmmonium heparin
   4. DSodium heparin

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   Answer: B · Lithium heparin

   Sodium heparin adds sodium to the sample and falsely raises plasma sodium, so lithium heparin is used for electrolytes. Ammonium heparin is unsuitable for ammonia and urea, because it adds ammonium. Lithium heparin in turn cannot be used when lithium itself is to be measured. Heparin prevents clotting by enhancing antithrombin, not by removing calcium.

   • A: A potassium salt would falsely raise the potassium.
   • C: Ammonium heparin is avoided for ammonia and urea.
   • D: Sodium heparin would falsely raise the sodium.

5. Question 5 · Hard

   Dipotassium EDTA is to be used at 1.5 mg per mL of blood, from a 10% w/v solution. What volume of solution is placed in a tube for 4 mL of blood?

   1. A15 µL
   2. B6 µL
   3. C60 µL
   4. D600 µL

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   Answer: C · 60 µL

   4 mL of blood needs 4 × 1.5 = 6 mg of EDTA. A 10% w/v solution contains 10 g per 100 mL, which is 100 mg/mL or 0.1 mg/µL. 6 mg ÷ 0.1 mg/µL = 60 µL, which is usually dried in the tube before use. Too much EDTA shrinks red cells and lowers the PCV, so the ratio of anticoagulant to blood matters.

   • A: 15 µL is the volume for 1 mL of blood, not 4 mL.
   • B: 6 µL treats 10% as 1 g per mL.
   • D: 600 µL treats 10% as 10 mg per mL.

6. Question 6 · Easy

   A 24-hour urine for vanillylmandelic acid (VMA) is collected in a container with:

   1. AThymol
   2. BFormalin
   3. CHydrochloric acid
   4. DSodium carbonate

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7. Question 7 · Medium

   Urine preserved with thymol may give a false-positive result in:

   1. ARothera's test for ketone bodies
   2. BBenedict's test for reducing sugar
   3. CAcid precipitation tests for protein
   4. DReagent strip tests for nitrite

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8. Question 8 · Easy

   A sample for neonatal serum bilirubin is left for 2 hours on a bench in direct sunlight. The result will be:

   1. AFalsely low
   2. BFalsely high
   3. CRaised by hemolysis
   4. DUnchanged

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9. Question 9 · Hard

   A man with chronic kidney disease has serum creatinine 6.2 mg/dL (reference 0.6-1.2) but blood urea 9 mg/dL (reference 15-40) by the urease-Berthelot method, on blood sent in a grey-top fluoride tube. The most likely explanation is:

   1. ACreatinine was falsely raised
   2. BFluoride inhibited the urease
   3. CLiver failure lowered the urea
   4. DOverhydration diluted the urea

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10. Question 10 · Medium

    Hemolysis of a blood sample falsely raises all of the following EXCEPT:

    1. APotassium
    2. BSodium
    3. CLactate dehydrogenase
    4. DAspartate aminotransferase

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11. Question 11 · Medium

    Blood in double (balanced) oxalate is unsuitable for blood urea by the urease method. Why?

    1. AIt hemolyzes the red cells
    2. BIt inhibits the enzyme urease
    3. CIt contains ammonium ions
    4. DIt precipitates the urea

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12. Question 12 · Hard

    A stone former's 24-hour urine, collected with 6 N HCl, gives a low uric acid result. Urine creatinine is 1.4 g/24 h (expected 1.0-2.0 g), and the container holds a reddish-brown gritty sediment. The most likely cause is:

    1. AA low-purine diet before the test
    2. BUric acid precipitated in the acid urine
    3. CPart of the collection was discarded
    4. DBacteria broke down the uric acid

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13. Question 13 · Easy

    How does potassium oxalate prevent blood from clotting?

    1. ABy binding calcium in a soluble chelate
    2. BBy inhibiting the enzymes of glycolysis
    3. CBy precipitating calcium as calcium oxalate
    4. DBy activating antithrombin in the plasma

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14. Question 14 · Medium

    A urine sent in a container with formalin gives an orange precipitate with Benedict's reagent. The likely reason is that formaldehyde:

    1. AActs as a reducing agent
    2. BMakes the urine alkaline
    3. CSplits sucrose into glucose
    4. DActs as an oxidizing agent

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15. Question 15 · Easy

    Which test has traditionally needed a 10-12 hour fast before the blood is collected?

    1. ASerum calcium
    2. BSerum triglycerides
    3. CSerum creatinine
    4. DSerum total protein

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16. Question 16 · Medium

    How does toluene, used as a urine preservative, mainly work?

    1. AForming a surface layer that keeps out air
    2. BFixing the cells and casts in the urine sediment
    3. CInhibiting glycolysis by blocking enolase
    4. DLowering the urine pH below 3

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17. Question 17 · Easy

    In a serum separator tube, the gel settles between the serum and the clot on centrifugation because its density is:

    1. AHigher than that of the packed red cells
    2. BLower than that of serum
    3. CEqual to that of serum
    4. DBetween that of serum and cells

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18. Question 18 · Medium

    Why does Wintrobe's double (balanced) oxalate combine ammonium oxalate and potassium oxalate in a 3:2 ratio?

    1. AThe mixture also stops glycolysis
    2. BAmmonium oxalate alone cannot bind calcium
    3. CTheir opposite effects on red cell size cancel out
    4. DPotassium oxalate alone causes hemolysis

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19. Question 19 · Medium

    Many samples from one ward arrive hemolysed. Which of these collection habits on the ward is the most likely cause?

    1. AGently inverting the tube 8 times
    2. BUsing a 21-gauge needle
    3. CForcing blood from a syringe through a fine needle
    4. DReleasing the tourniquet within a minute

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20. Question 20 · Easy

    For most chemistry tests, within about how long of collection should serum or plasma be separated from the cells?

    1. A15 minutes
    2. B6 hours
    3. C24 hours
    4. D2 hours

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21. Question 21 · Easy

    Sodium fluoride preserves blood glucose by inhibiting which glycolytic enzyme?

    1. AHexokinase
    2. BGlucose oxidase
    3. CEnolase
    4. DPyruvate kinase

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22. Question 22 · Easy

    A blood sample for glucose arrives in the laboratory with no name or other identifier on the tube. What should be done?

    1. ATest it and label it from the request form
    2. BReject it and request a new sample
    3. CTest it and report it with a comment
    4. DAsk the porter who brought it to label it

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23. Question 23 · Easy

    In what ratio is 3.2% trisodium citrate mixed with blood for coagulation tests?

    1. A1 part citrate to 4 parts blood
    2. B1 part citrate to 1 part blood
    3. C1 part citrate to 9 parts blood
    4. D1 part citrate to 19 parts blood

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24. Question 24 · Medium

    Unseparated blood is kept overnight in a refrigerator at 4 °C before the serum is removed. Which result is most affected?

    1. APotassium, falsely high
    2. BPotassium, falsely low
    3. CBicarbonate, falsely high
    4. DSodium, falsely high

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25. Question 25 · Hard

    An outpatient's potassium is 6.3 mEq/L (reference 3.5-5.0) with no hemolysis, calcium 9.4 mg/dL and a normal ECG; the serum was separated within 30 minutes. He pumped his fist repeatedly during collection. A careful repeat gives 4.2 mEq/L. The first result is best explained by:

    1. AHemolysis during collection
    2. BPotassium from working forearm muscle
    3. CDelayed separation of serum
    4. DK2EDTA carry-over

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