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2.2 Haematology > Practical 7: Coagulation > Flashcards

Practical 7: Coagulation Flashcards

1
Q

What are the three coagulation tests carried out in the lab?

A

Prothrombin Time (PT)

Activated Partial Thrombin Time (APTT)

Thrombin Time (TT)

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2
Q

What coagulation test may have to be carried out if there is an abnormality/a prolonged time?

A

Correction/mixing studies

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3
Q

How many phases are there to haemostasis?

A

Three phases

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4
Q

What are the three phases of haemostasis?

A

Primary

Secondary

Tertiary

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5
Q

What does the APTT and the PT measure

A

They measure the time elapsed from activation of the coagulation cascade at different point to the generation of fibrin

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6
Q

What must always be checked before running a coagulation test?

A

Check the patients platelet levels

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7
Q

How should a sample be taken for coagulation testing
(2)

A

Blood must be taken into a bottle which contains sodium citrate anticoagulant

The sample must be analysed within 4 hours of being taken

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8
Q

What is the preferred ratio of anticoagulant to blood?

A

1:9

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9
Q

Why is the ratio of anticoagulant to blood so important?

A

The sample must not have clotted or haemolysed as this will interfere with the accuracy of the coagulation tests

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10
Q

What exactly does the PT measure

A

Measures the time necessary to generate fibrin after activation of factor VII

It measures the integrity of the extrinsic and common pathways

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11
Q

What factors are examined in the PT test

A

Fibrinogen (1), Prothrombin (2), 5, 7, 10,

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12
Q

What exactly does the APTT measure

A

Measures the time necessary to generate fibrin from initiation of the intrinsic pathway

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13
Q

What factors are examined in the APTT test

A

Fibrinogen (I)

Prothrombin (II)

V

VIII

IX

X

XI

XII

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14
Q

How is the APTT test ran without activating the PT

A

By using an external agent (e.g. kaolin) capable of activating factor XII without activating factor VII

Since platelet factors are necessary for the cascade to function normally, the test is performed in the presence of a phospholipid emulsion that takes the place of these factors

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15
Q

What exactly does thrombin time measure

A

It measures the time necessary to drive the reaction of fibrinogen to fibrin in the presence of thrombin

It measures the intensity of this reaction and isolates an abnormality to either a decrease in normal fibrinogen or an inhibitor to its activation

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16
Q

What causes haemophilia A

A

Loss of factor VIII

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17
Q

What causes haemophilia B

A

Loss of factor IX (9)

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18
Q

What would cause a deficiency of fibrinogen
(5)

A

A consumptive coagulopathy

Severe liver disease

Hereditary deficiencies

Afibrinogenaemia

Dysfibrinogenaemia -> acquired (liver disease) or inherited

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19
Q

What can affect TT -> fibrinogen to fibrin

A

Inhibitors such as heparin and dabigatran

20
Q

How can you reverse the affects of anticoagulants on TT

A

Catalyse the reaction with reptilase

Unlike thrombin, reptilase is insensitive to heparin and dabigatran

21
Q

When and why is a mixing/correction study carried out
(2)

A

Used for the investigation of prolonged blood coagulation screening tests

Purpose is to determine if the prolongation is due to a factor deficiency or an inhibitor

22
Q

Comment on the results of a mixing/correction study
(2)

A

If a factor(s) is deficient in the patients plasma there will be a shortening of the prolonged screening test

The presence of an inhibitor should result in no correction or minimal correction of the screening test

23
Q

How is a mixing/correction study carried out?
(3)

A

Plasma from a patient with an abnormal PT and/or aPTT is mixed in equal volumes (1:1) with normal pooled plasma (a source of normal levels of all coagulation factors)

The sample is then analysed by the required method i.e. PT or APTT

Use the Rosner Index to determine if there has been a correction or not

24
Q

What should you do if your mixing/correction study gives a corrected result

A

Incubate the sample for 1 hour at 37 degrees and reanalyse to determine if there is a time or temperature dependent inhibitor e.g. Haemophilia or lupus anticoagulant

25
Q

What should you do if your mixing/correction study identifies a factor deficiency

A

A factor assay is then carried out to determine the quantity of the factor that is present

26
Q

What is Lupus anticoagulant?

A

Antiphospholipid antibodies usually IgG and rarely IgM directed against plasma proteins e.g. prothrombin bound to anionic phospholipids

27
Q

How common are lupus anticoagulants

A

Seen in 5-10% of systemic lupus patients

28
Q

How do lupus anticoagulants affect coagulation tests
(2)

A

They block the in vitro assembly if the prothrombinase complex

This results in a prolongation of protein assays such as APTT and rarely PT

29
Q

What is the prothrombinase complex

A

Factor Xa and Factor V assembled on negatively charged phospholipid membranes in the presence of calcium ions

30
Q

Why is thrombosis so common in lupus patients even if they cant for the prothrombinase complex?

A

Its not really understood but it may involve IgG binding to phospholipids that are essential for the normal activating and degrading effects of protein C and protein S, thus shifting the balance in favour of thrombus formation

31
Q

List six errors that can occur when taking a blood sample

A

Short draw -> not enough blood

Failure to mix specimen after collection

Excessive vigorous mixing

Haemolysis

Improper storage

Chilling in refrigerator or placing on ice

32
Q

What factors are vitamin K dependent

A

II

VII

IX

X (Protein C, protein S)

33
Q

What anti-coagulant affects vitamin K dependant factors?

A

Warfrin

34
Q

What is the equation for the Rosner Index

A

(1:1 mix clotting time result - NPP clotting time result)/ initial prolonged clotting of patient sample

35
Q

What is a high Rosner Index and what does it mean

A

High index > 15% indicates inhibitor

Low index < 15% indicates deficiency

36
Q

What diseases would cause a normal PT and ATPP
(5)

A

Von Willebrand’s disease

FXII deficiency

Dysfibrinogenemia

Platelet dysfunction

a-antiplasmin deficiency

37
Q

What three diseases would cause a prolonged PT, a normal APTT and a corrected mixing study?

A

Hereditary = isolated FVII deficiency

Acquired = vitamin K deficiency or severe liver impairment

38
Q

What two diseases would cause a prolonged PT, a normal APTT and no corrected mixing study?

A

Lupus anticoagulant

FVII inhibitor (rare)

39
Q

What five diseases would cause a normal PT, a prolonged APTT and a corrected mixing study?

A

Bleeding:
- FVIII/vWD deficiency
- FIX/XI deficiency

No bleeding:
- FXII
- HMWK
- prekallikrein

40
Q

What 8 diseases would cause a normal PT, a prolonged APTT and no corrected mixing study?

A

Bleeding:
- FVII
- FIX
- FXI inhibitor
- heparin

No bleeding:
- FXII inhibitor
- lupus anticoagulant
- HMWK
- prekallikrein

41
Q

What five diseases would cause a prolonged PT, a prolonged APTT and a corrected mixing study?

A

FII, FV, FX deficiency

FV and FVII deficiency

Severe liver impairment

Vitamin K deficiency

DIC

42
Q

What two diseases would cause a prolonged PT, a prolonged APTT and no corrected mixing study?

A

FII, FV, FX inhibitor

Lupus anticoagulant

43
Q

What is the normal range for PT

A

10-14 seconds

44
Q

What is the normal range for APTT

A

21-35 seconds

45
Q

What is the normal range for TT

A

10-16 seconds

2.2 Haematology (38 decks)

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