Haemostasis and coagulation tests

40 Lab technician recruitment practice questions on Haemostasis and coagulation tests, part of Haematology. 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

   The reference range of the platelet count in healthy adults is about:

   1. A15,000-40,000/µL
   2. B4,000-11,000/µL
   3. C1.5-4.0 lakhs/µL
   4. D40-60 lakhs/µL

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   Answer: C · 1.5-4.0 lakhs/µL

   Healthy adults have about 1,50,000 to 4,00,000 platelets per µL (150-400 × 10^9/L); some laboratories take 4.5 lakhs as the upper limit. A count below 1.5 lakhs is thrombocytopenia, and one above the upper limit is thrombocytosis. Spontaneous bleeding becomes a risk when the count falls very low, usually below about 20,000/µL. Every unexpectedly low count should be checked on a blood film.

   • A: A count of 15,000-40,000/µL is severe thrombocytopenia.
   • B: This is the leucocyte (WBC) count range.
   • D: This is the order of the red cell count, in lakhs per µL.

2. Question 2 · Easy

   The WHO primary international reference thromboplastin has, by definition, an ISI of:

   1. A0.1
   2. B2.5
   3. C10.0
   4. D1.0

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   Answer: D · 1.0

   Each commercial thromboplastin is calibrated against the WHO reference preparation, which is assigned an ISI of 1.0. A reagent with an ISI close to 1.0 is about as sensitive as the reference. Reagents with high ISI values are less sensitive and give less precise INRs. The ISI is printed on the reagent insert for each lot.

   • A: An ISI of 0.1 is not a realistic thromboplastin value.
   • B: An ISI of 2.5 marks an insensitive reagent, not the reference.
   • C: An ISI of 10 is far outside the range of real reagents.

3. Question 3 · Easy

   The calcium chloride used to recalcify plasma in the PT and aPTT is usually of strength:

   1. A0.109 M
   2. B2.5 M
   3. C0.025 M
   4. D0.25 M

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   Answer: C · 0.025 M

   Citrate stops clotting by binding calcium, so calcium must be added back to start the reaction. A 0.025 M (25 mmol/L) calcium chloride solution, warmed to 37 °C, is standard for both tests. Stronger solutions do not speed clotting and excess calcium can even inhibit it. The reagent is checked with normal and abnormal controls in every run.

   • A: 0.109 M is the strength of the trisodium citrate anticoagulant.
   • B: 2.5 M calcium chloride is far too concentrated for coagulation work.
   • D: A tenfold stronger solution is not used and can inhibit clotting.

4. Question 4 · Easy

   The international normalised ratio (INR) is calculated as:

   1. A(Patient PT - mean normal PT) multiplied by ISI
   2. B(Patient PT ÷ mean normal PT) raised to the ISI
   3. C(Patient PT ÷ mean normal PT) multiplied by ISI
   4. D(Mean normal PT ÷ patient PT) raised to the ISI

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   Answer: B · (Patient PT ÷ mean normal PT) raised to the ISI

   The PT ratio is the patient's PT divided by the laboratory's mean normal PT. Raising the ratio to the power of the thromboplastin's international sensitivity index (ISI) gives the INR. This corrects for differences in reagent sensitivity, so INRs from different laboratories can be compared. The INR is valid for patients stable on vitamin K antagonists such as warfarin.

   • A: A difference in seconds is not used in the INR.
   • C: Multiplying by the ISI is a common error; ISI is an exponent.
   • D: The ratio is inverted; a prolonged PT would give an INR below 1.

5. Question 5 · Easy

   Haemophilia A is inherited as:

   1. AA Y-linked trait
   2. BAn autosomal dominant trait
   3. CAn X-linked recessive trait
   4. DAn autosomal recessive trait

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   Answer: C · An X-linked recessive trait

   The factor VIII gene lies on the X chromosome, so haemophilia A is X-linked recessive. Males with one affected X are affected, while females with one affected X are usually carriers. About a third of cases arise from new mutations with no family history. Haemophilia B (factor IX) follows the same pattern.

   • A: No coagulation factor gene lies on the Y chromosome.
   • B: Von Willebrand disease type 1 is the common autosomal dominant bleeding disorder.
   • D: Most rare factor deficiencies, such as factor XIII, are autosomal recessive.

6. Question 6 · Medium

   A raised plasma fibrinogen level is most commonly due to:

   1. AAn acute-phase response
   2. BThrombolytic therapy
   3. CSevere liver failure
   4. DDisseminated intravascular coagulation

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7. Question 7 · Easy

   Bleeding into joints and deep muscles is most typical of which group of disorders?

   1. APlatelet function disorders
   2. BVascular purpuras
   3. CThrombocytopenias
   4. DCoagulation factor deficiencies

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8. Question 8 · Medium

   In factor VIII inhibitor testing, one Bethesda unit is the amount of inhibitor that:

   1. ADestroys all the factor VIII in normal plasma
   2. BNeutralises one unit of factor VIII per mL
   3. CProlongs the aPTT of normal plasma by 10 s
   4. DDestroys half the factor VIII in normal plasma

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9. Question 9 · Medium

   A boy with a history suggestive of mild haemophilia A has a normal aPTT. What is the best next test?

   1. AThrombin time
   2. BFactor VIII assay
   3. CProthrombin time
   4. DBleeding time

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10. Question 10 · Medium

    In the first one or two days of warfarin therapy, the PT rises mainly because of a fall in:

    1. AFactor X
    2. BFibrinogen
    3. CFactor VII
    4. DProthrombin

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11. Question 11 · Hard

    A Clauss fibrinogen clots too fast to read at the usual 1 in 10 dilution. At 1 in 20, the curve (made at 1 in 10) reads 280 mg/dL. What fibrinogen should be reported?

    1. A2,800 mg/dL
    2. B140 mg/dL
    3. C560 mg/dL
    4. D280 mg/dL

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12. Question 12 · Medium

    A citrate sample for PT was kept in the refrigerator for several hours before testing. The main concern is that cold storage:

    1. ALyses all the platelets
    2. BInactivates thromboplastin
    3. CPrecipitates the citrate
    4. DActivates factor VII

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13. Question 13 · Hard

    With a thromboplastin of ISI 2.0, a warfarin patient's PT ratio is 1.5. What is the INR, judged against the usual target of 2.0-3.0?

    1. A1.22, below target
    2. B2.25, within target
    3. C1.5, below target
    4. D3.0, at the upper limit

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14. Question 14 · Medium

    Which test is normal in a patient with severe haemophilia A?

    1. ABleeding time
    2. BaPTT
    3. CFactor VIII assay
    4. DLee and White clotting time

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15. Question 15 · Hard

    A child with fever for 5 days has dengue NS1 positive. Platelets 28,000/µL; PT, aPTT and fibrinogen are normal. Which further result is most likely?

    1. ALow factor VIII level
    2. BProlonged clotting time
    3. CProlonged bleeding time
    4. DProlonged thrombin time

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16. Question 16 · Medium

    Which test is prolonged by both heparin and a low fibrinogen, but stays normal in factor VIII deficiency?

    1. ALee and White clotting time
    2. BPlatelet count
    3. CThrombin time
    4. DaPTT

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17. Question 17 · Easy

    The thrombin time measures the:

    1. ABreakdown of fibrin to D-dimer
    2. BRelease of platelet granules
    3. CActivation of factor X
    4. DConversion of fibrinogen to fibrin

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18. Question 18 · Medium

    In a one-stage factor VIII assay, the 100% calibration curve is made from dilutions of:

    1. ANormal aged serum
    2. BCalibrated pooled normal plasma
    3. CBarium sulphate-adsorbed plasma
    4. DThe patient's own undiluted plasma

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19. Question 19 · Hard

    A man bitten by a Russell's viper has a non-clotting 20WBCT and receives anti-snake venom. By the Indian protocol, when should the 20WBCT be repeated?

    1. A6 hours after the ASV dose
    2. B15 minutes after the ASV dose
    3. COnly if bleeding is visible
    4. D24 hours after the ASV dose

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20. Question 20 · Medium

    On an impedance analyser, very small red cells and red cell fragments tend to make the platelet count:

    1. AFalsely high
    2. BUnchanged
    3. CFalsely low
    4. DUnreadable

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21. Question 21 · Medium

    A boy with haemarthrosis has factor VIII activity of 3% and a normal VWF level. His haemophilia A is classed as:

    1. AMild
    2. BModerate
    3. CSevere
    4. DCarrier state

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22. Question 22 · Easy

    Which coagulation factor is known as the labile factor?

    1. AFactor V
    2. BFactor II
    3. CFactor VII
    4. DFactor X

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23. Question 23 · Hard

    A jaundiced man has a PT of 22 s (control 13 s). After vitamin K injection for 3 days, the PT is 14 s. Which cause of jaundice fits best?

    1. AGilbert syndrome
    2. BHaemolytic jaundice
    3. CObstructive jaundice
    4. DHepatocellular disease

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24. Question 24 · Easy

    Which substance is added to aPTT reagent as the contact activator?

    1. ATissue factor
    2. BKaolin
    3. CRistocetin
    4. DThrombin

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25. Question 25 · Easy

    In the Duke method of bleeding time, the drop of blood at the puncture is blotted with filter paper every:

    1. A5 minutes
    2. B5 seconds
    3. C2 minutes
    4. D30 seconds

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