BMS218 > Coagulation Screening Tests > Flashcards

Coagulation Screening Tests Flashcards

(73 cards)

Study These Flashcards
1
Q

What type of sample is collected for coagulation testing?

A

Venous whole blood collected by venepuncture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What anticoagulant is used for coagulation testing samples?

A

3.2% sodium citrate (commonly known as the blue top tube).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the correct blood-to-anticoagulant ratio for coagulation samples?

A

9:1 (blood : anticoagulant).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What should be ensured immediately after blood collection into a citrate tube?

A

The sample must be well mixed with the anticoagulant to prevent clotting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What tests can be performed directly on anticoagulated whole blood?

A

Platelet function testing.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How is platelet-rich plasma (PRP) prepared?

A

Centrifuge whole blood at 150 g for 10 minutes (or similar)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How is platelet-poor plasma (PPP) prepared?

A

Centrifuge whole blood at 1500 g for 15 minutes (or similar)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Which plasma fraction is used for coagulation testing?

A

The plasma supernatant (platelet-poor plasma, PPP).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

At what temperature should coagulation specimens be stored after collection?

A

Room temperature (18–24°C).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Within what time frame should coagulation testing generally be completed after collection?

A

Within 4 hours of collection.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How soon should whole blood or PRP be tested for platelet studies?

A

Within 3 hours of collection.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How can platelet-poor plasma (PPP) be stored for longer periods?

A

It can be frozen and stored at –80°C for up to 6 months.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What storage conditions should be avoided and why?

A

1–6°C: Damages platelet integrity

Above 25°C: Causes factor VIII (FVIII) deterioration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Why should plastic tubes be used for coagulation testing instead of glass?

A

Because glass tubes can activate some clotting factors, leading to false results.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Why are siliconised (plastic-coated) glass tubes unsuitable for specimen collection?

A

They can break easily, posing a pathogen exposure risk.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why is noting the patient’s clinical history important in haemostasis testing?

A

Because some drugs affect coagulation results.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How does aspirin affect haemostasis testing?

A

It interferes with the cyclo-oxygenase pathway in platelets, reducing platelet function.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How does warfarin affect coagulation tests?

A

It inhibits factors II, VII, IX, and X, prolonging PT.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why should clotted specimens be avoided in coagulation testing?

A

They indicate insufficient anticoagulant or poor mixing, invalidating results.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What problems can excessive agitation of a specimen cause?

A

It can cause haemolysis, activation of procoagulants, and platelet activation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are the coagulation screening tests?

A

(Platelet count / morphology)
(Bleeding time) - dont do this any more
Prothrombin time (PT)
Activated partial thromboplastin time (PTT)
Thrombin clotting time
Fibrinogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the primary role of platelets in haemostasis?

A

Platelets are required for normal haemostasis — they form the initial plug and provide a surface for clotting reactions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

At what platelet count does mild bleeding risk begin?

A

< 100 × 10⁹/L → Mild bleeding risk

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

At what platelet count is bleeding risk considered moderate?

A

< 50 × 10⁹/L → Moderate bleeding risk

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
At what platelet count is the bleeding risk severe?
< 20 × 10⁹/L → Severe bleeding risk.
26
How does platelet morphology relate to function?
There is a good correlation; abnormal platelet morphology usually indicates abnormal function
27
What is the principle of the bleeding time test?
A small, standardised skin injury is made, and the time for bleeding to cease is measured.
28
What does the Bleeding Time test reflect?
The integrity of platelets and capillary (microcirculation) function.
29
What aspect of haemostasis does the Bleeding Time assess directly?
It is the only direct physiological test of primary haemostasis (platelet + vessel wall interaction).
30
What are the main problems with the traditional Bleeding Time test?
Poor standardisation Limited sensitivity Questionable usefulness as a routine pre-operative screening test Limited value for characterising some bleeding disorders
31
What test has largely replaced the Bleeding Time test?
The Platelet Function Analyser (PFA).
32
What is the principle of the Platelet Function Analyser (PFA)?
It measures the time it takes for occlusion of a small aperture in a membrane by activated platelets under flow conditions.
33
What are the PFA test cartridges coated with?
Either Collagen/Adrenaline or Collagen/ADP.
34
What is the main advantage of the Platelet Function Analyser (PFA)?
It provides a quick screening test for platelet function.
35
What are the two major coagulation screening tests?
Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT).
36
What is the principle behind both PT and aPTT tests?
They use excessive amounts of a reagent (trigger) to initiate the clotting reaction so we know which pathway we are testing
37
What is the endpoint of both PT and aPTT tests?
Formation of an insoluble fibrin clot
38
How is the fibrin clot detected in manual methods of PT/aPTT testing?
The fibrin clot is visualised directly by the operator
39
How is the fibrin clot detected in automated methods of PT/aPTT testing?
The fibrin clot is detected by optical and mechanical principles
40
What reagent combination forces coagulation reactions through the extrinsic pathway in vitro?
Addition of tissue factor (TF) and calcium ions (Ca²⁺).
41
Which laboratory test measures the extrinsic pathway?
The Prothrombin Time (PT) test
42
Which clotting factors are required for the Prothrombin Time (PT) test?
Factors I, II, V, VII, and X
43
What reagent combination forces coagulation reactions through the intrinsic pathway in vitro?
Addition of phospholipid (PL) or platelet membranes, calcium ions (Ca²⁺), and an activator of factor XII.
44
Which laboratory test measures the intrinsic pathway?
The Activated Partial Thromboplastin Time (aPTT) test (previously called PTT).
45
Which clotting factors are required for the aPTT test?
Factors I, II, V, VIII:C, IX, X, XI, and XII.
46
What is the reagent composition of thromboplastin used in a PT test?
Tissue factor, phospholipids, and calcium
47
What sample is mixed with thromboplastin in a PT test?
Plasma (100 µL), either normal control or patient specimen.
48
The PT test reactions proceed through which pathways?
The extrinsic and common coagulation pathways.
49
What is the endpoint of the PT test?
Formation of a visible or instrument-detected fibrin clot.
50
How is PT reported?
As clotting time in seconds, to 1 decimal place.
51
What does INR stand for?
International Normalised Ratio.
52
What are the major causes of a prolonged PT?
Clotting factor deficiencies (VII, X, V, II, I) Oral anticoagulant therapy (Warfarin) Liver disease Vitamin K deficiency
53
What is the formula for calculating INR?
Clotting time of the patient in seconds, divided by the clotting time of the control plasma in seconds, to the power of the International Sensitivity Index of the thromboplastin reagent
54
Why is the ISI (International Sensitivity Index) used in INR calculation?
To standardise results between laboratories using different thromboplastin reagents
55
How is INR typically reported?
To 1 decimal place.
56
What is added to trigger clot formation in the aPTT test?
Calcium chloride
57
What reagents are mixed in the aPTT test?
Partial thromboplastin (100 µL) Patient or control plasma (100 µL) Activator (100 µL), e.g., negatively charged kaolin
58
Through which pathways does the aPTT reaction proceed?
The intrinsic and common coagulation pathways.
59
What is the endpoint of the aPTT test?
Formation of a fibrin clot, with clotting time recorded.
60
What are the major causes of a prolonged aPTT?
Clotting factor deficiencies: I, II, V, VIII, IX, X, XI, XII Lupus anticoagulants Acquired inhibitors (e.g., anti-VIII, anti-IX) Anticoagulant therapy monitoring: Unfractionated heparin (UFH)
61
What is the principle of a mixing study?
Mix patient plasma (50 µL) with normal control plasma (50 µL) and run an aPTT to distinguish between factor deficiencies and inhibitors.
62
What result indicates a factor deficiency in a mixing study?
The prolonged aPTT corrects to the normal range after mixing with normal plasma.
63
What result indicates the presence of an inhibitor in a mixing study?
The aPTT shortens but does not fully correct to the normal range.
64
What is the purpose of mixing studies?
Helps distinguish between: Factor deficiencies (corrected by normal plasma) Inhibitors (autoantibodies or drugs, not corrected)
65
What does the Thrombin Clotting Time (TCT) test assess?
The levels and function of fibrinogen in plasma.
66
How is the TCT performed?
Mix excess thrombin with patient or control plasma at 37°C and record the time to fibrin clot formation.
67
Which clotting factors are bypassed in the TCT test?
All factors except fibrinogen are bypassed. Testing the clotting endpoint of fibrinogen getting cleaved to fibrin.
68
What are the main causes of a prolonged TCT?
Hypofibrinogenaemia (low fibrinogen) Afibrinogenaemia (absent fibrinogen) Dysfibrinogenaemia (abnormal fibrinogen function)
69
What other factors should be excluded if TCT is prolonged?
Heparin, paraproteins, or fibrin degradation products (FDPs)
70
What is the Clauss Method used for?
It is a clotting assay recommended for determining the functional activity of fibrinogen.
71
How is the Clauss Method performed?
Add bovine thrombin to diluted patient or control platelet-poor plasma Measure clotting time Compare to a standard curve of known fibrinogen concentrations
72
What are some other methods for fibrinogen measurement?
Turbidometric: Absorbance derived from PT/aPTT Immunological Chemical: Ratnof & Menzie method
73
What is the key difference between functional vs total fibrinogen?
Functional (activity): Measures the ability of fibrinogen to form a clot Total (antigen): Measures total fibrinogen protein regardless of functionality
BMS218
flashcards
Decks in class (29)
# Cards
Brainscape helps you reach your goals faster, through stronger study habits.
© 2026 Bold Learning Solutions. Terms and Conditions