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2.2 Haematology > Laboratory Investigation of Haemostatic Disorders > Flashcards

Laboratory Investigation of Haemostatic Disorders Flashcards

1
Q

Why does a patient present to a haemostasis clinic?
(4)

A

Patient presents with personal history of bleeding of bleeding or thrombosis

Family history of bleeding or thrombosis

Unexpected results in coagulation screen

Prior to surgery

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2
Q

What are the two ways of preparing blood for analysis

A

Whole blood from finger-pricks, for immediate, on site-analysis -> used in coagulation clinics or home tests

Blood samples are collected in laboratory test tubes (vacutainers) for remote analysis -> for laboratory testing, usually stored in an anti-coagulant

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3
Q

Give three anti-coagulants used in blood

A

EDTA (pink or purple) -> for full blood count

Heparin (green) -> usually biochemistry

Other (serum samples, clot activator)

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4
Q

What is the basis of coagulation?

A

Coagulation requires the presence of Ca++

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5
Q

How does EDTA work?

A

Irreversible binding calcium

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6
Q

How does sodium citrate work

A

Binds the calcium but not as strongly as EDTA

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7
Q

How does acid-citrate dextrose (ACD) work?
(2)

A

A solution of citric acid, sodium citrate and dextrose in water

Used for tissue typing

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8
Q

How does heparin work?

A

Prevents the actions of thrombin (Factor II)

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9
Q

What are some pre-analytical variables for coagulation samples

A

Underfilling/overfilling of sample container, HCT concentration

Delay in sample analysis (< 4 hours)

Collection of blood through a line contaminated with Heparin, recognition of the interference of drugs on haemostasis

Clean venepuncture, needle gauge from 22-19

Patients should be relaxed and in a warm atmosphere

Venous blood, minimum stasis, no venous occlusion

Tri-sodium citrate, 105mmol or 109mmol, Ratio 1:9

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10
Q

What are the five main tests used to assess blood clotting function?

A

Platelet count (done on EDTA FBC sample)

Prothrombin Time (PT), INR: Assess function of the Extrinsic Pathway (Tissue Factor Pathway)

Activated Partial Thromboplastin Time (APTT) to assess function of the intrinsic pathway

Thrombin time

Fibrinogen

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11
Q

What is an INR
(5)

A

International Normalised Ratio

Used for people on warfarin

Narrow therapeutic window which needs to be monitored

Uses the PT of patient/normal patient -> to the power of the ISI value

ISI -> international sensitivity index

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12
Q

What is the function of using INR
(6)

A

Takes into account that each lab might use different PT reagents

Only used to monitor warfarin

Makes sure your not under or over dossing

Needs to be between 2 and 3

If INR is a little high might be advised to skip a dose

If INR very high might be administered vitamin K

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13
Q

What is prothrombin time (PT)
(6)

A

Sensitive to factor II, V, VII, X and fibrinogen (I) (extrinsic system(

Thromboplastin is added to the patients plasma, along with calcium chloride which activates factor VII and the extrinsic pathway continues

The time it takes for the clot to form is recorded

The test is done in a glass test tube at 37 degrees

Normal range of 10-14 seconds, all laboratories must determine their own normal range

This test is used to monitor warfarin therapy

A prolonged PT may indicate a disorder of clotting processes

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14
Q

Why was INR put in place
(3)

A

PT result on a normal individual will vary according to the type of analytical system employed

Due to variations between different batches of tissue factor used in the reagent to perform the test

Each manufacturer assigns an ISI value for any TF they manufacture, this indicates how their batch of TF compares to an international reference tissue factor

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15
Q

What is considered a normal INR

A

1.1 or below

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16
Q

What is the INR effective therapeutic range for warfarin?

A

Between 2.0 and 3.0

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17
Q

What warfarin INR requires intervention?
(2)

A

INR greater than 10
Reduce warfarin and administer vitamin K

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18
Q

What six factors influence INR?

A

Drugs
Illness especially liver disease
Nutritional intake e.g. cabbage, spinach are rich in vitamin K and therefore can affect the INR
Smoking, alcohol consumption
Physical and mental stress
Climatic variations during travel

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19
Q

What is APTT

A

Activated Partial Thromboplastin Time

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20
Q

What is APTT?
(6)

A

The test measures the clotting time of plasma after the activation of the contact factors (Prekalikren, high molecular weight kininogen, XI and XII)

The APTT is termed ‘partial’ due to the absence of tissue factor from the reaction mixture

It measures the factors XII, XI, X, IX, VIII, V, II and I (intrinsic pathway)

Activation is caused by the addition of kaolin, phospholipid and CaCl2

The reference range normally reported is between 21-35 seconds and depends on the reagents used, each lab establishes their own range

APTT testing is used to monitor heparin therapy

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21
Q

How is the APTT activated

A

Caused by the addition of kaolin, phospholipid and CaCl2

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22
Q

What are the three steps to APRR?

A

Activation of coagulation with Silica
Incubation for 5 minutes at 37 degrees
Calcium is added and this triggers clot formation

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23
Q

What might cause a prolonged APTT and a normal PT
(5)

A

Deficiency of factor VIII, IX or XI

Inhibitor factor of VIII, IX or XI

Von Willebrand’s disease

Unfractionated heparin

Direct thrombin inhibitors

24
Q

What would cause a normal APTT and prolonged PT?
(5)

A

Deficiency o f factor VII
Inhibitor of factor VII
Vitamin K deficiency
Liver disease
Warfarin

25
Q

What would cause a prolonged APTT and prolonged PT

A

Deficiency of prothrombin, fibrinogen, factor V, or factor X

Inhibitor of prothrombin, fibrinogen, factor V or factor X

Supratherapeutic doses of heparin or warfarin

Liver disease

Disseminated intravascular coagulation

Argatroban

26
Q

What would cause a prolonged APTT and prolonged PT
(5)

A

Deficiency of prothrombin, fibrinogen, factor V, or factor X

Inhibitor of prothrombin, fibrinogen, factor V or factor X

Supratherapeutic doses of heparin or warfarin

Liver disease

Disseminated intravascular coagulation

Argatroban

27
Q

How can you overcome heparin contamination?
(3)

A

Use reptilase time test to confirm this is heparin coagulation prolonging the APTT

The reptilase isn’t sensitive to heparin

This is purified from snake venom

28
Q

What is thrombin time?
(4)

A

Can sometimes be part of a coagulation screen, depending on the laboratory

Thrombin is added to plasma and fibrinogen is converted to fibrin

Time taken for clot formation is measured

Normal Range is 15-23 seconds

29
Q

What are four causes of abnormal Thrombin Time

A

Dysfibrinogenaemia (abnormal form of fibrinogen) -> Congenital, liver disease or neonate

Hypofibrinogenaemia (decreased fibrinogen) -> DIC or congenital deficiency

Increased levels of Fibrin Degradation Products -> DIC/liver disease

Heparin contamination -> exclude with reptilase time

30
Q

What is reptilase time?
(6)

A

If there is elevated TT, elevated APTT and normal PT

Need to confirm if prolonged results are due to heparin contamination through RT

RT is similar to TT except Bothrops atrox, a thrombin-like enzyme purified from snake venom is used

Heparin is an anticoagulant which works by increasing the power of anti-thrombin

Reptilase is unaffected by anti-thrombin (heparin) so the RT will be normal

A normal RT in conjunction with a prolonged TT is diagnostic of the presence of Heparin in a sample

31
Q

What would indicate dysfibrinogenaemia?

A

Abnormal TT
Abnormal RT

32
Q

What would indicate elevated D dimers

A

Abnormal TT
Abnormal RT

33
Q

What would indicate heparin in sample

A

Abnormal TT
Normal RT

34
Q

What is fibrinogen?
(3)

A

Fibrinogen is the largest protein of the coagulation system

It is the substrate for the coagulation reaction

Normal range is 1.5-4g/L

35
Q

How do we carry out a fibrinogen assay?
(5)

A

Plasma is diluted in Owrens buffer

Thrombin is added to diluted plasma

Fibrinogen is converted to fibrin

The fibrin undergoes polymerisation to form a fibrin mesh

Activated factor XIII stabilises this mesh to form a visible clot

36
Q

What are two congenital disorders of fibrinogen

A

Afibrinogenaemia
Dysfibrinogenaemia

37
Q

What are four acquired disorders of fibrinogen

A

Quantitative or qualitative
DIC
Sever blood loss
Liver disease

38
Q

When and why are correction/mixing studies/test carried out?
(6)

A

May be performed when a prolonged PT or the APTT is found

In order to narrow down the cause, control normal plasma is mixed with the patient’s plasma and the test is repeated

If a correction is made, then the control normal plasma which contains all the coagulation factors which was added to the patient’s plasma has corrected the deficiency in the patient

Addition of control normal plasma to patient plasma

Look for correction

Test at T0 and T60 after incubation at 37 degrees Celsius

39
Q

What does correction by mixing studies indicate

A

Factor deficiency

40
Q

What does no correction by mixing studies indicate?
(2)

A

Lupus anticoagulant

Specific factor inhibitor

41
Q

What are factor assays?
(5)

A

If a factor deficiency is suspected this is confirmed by carrying out a factor assay for that particular factor

An abnormal level of any coagulation factor is verified by repeat assay

Patient is tested on a number of occasions

Three abnormal factor levels: patient registered as deficient

Siblings and family are then tested

42
Q

What are D-Dimer Test?
(3)

A

Fibrin split product

Circulating half life of 4-6 hours

Quantitative test have 80-85% sensitivity and 93-100% negative predictive value

43
Q

What might cause a false positive D-Dimers?
(10)

A

Pregnant patients
Malignancy
Advanced age > 80 years
Haemorrhage
Hepatic impairment

Less than 1 week post partum
Surgery within 1 week
Sepsis
CVA
Collagen vascular diseases

44
Q

What are D-Dimers?
(5)

A

Specific degradation product of cross-linked fibrin

Released when cross-linked fibrin is degraded by plasmin

Indirect measurement of thombin generation and subsequent clot formation

The only marker of thrombotic disorders that indicate the presence of stabilised fibrin

Marker of activation of coagulation and fibrinolysis

45
Q

When do we want to see high D-dimers?

A

After labour or surgery
We want to see clots being formed

46
Q

What does elevated D-Dimers indicate?
(3)

A

Indicates the occurrence of recent thrombotic event

It doesn’t differentiate between appropriate thrombosis (wound healing) or inappropriate thrombosis (pathological thrombi)

A normal D-Dimer Concentration excludes thrombo-embolic events such as DVT and PE with a very high probability

47
Q

When might D-Dimers be measured?
(3)

A

Patient with suspected venous thromboembolism

Doctor determines clinical probability according to clinical decision rule

Determined as high clinical probability

D-Dimer measured

Imaging examination to confirm of refute diagnosis

48
Q

What might elevated D-dimer levels cause
(14)

A

DVT
PE
DIC
Old age Pregnancy
Pathological pregnancies
Coronary disease
Thrombolytic therapy
Cancer
Liver disease
Infection
Inflammation
haematoma
Peripheral arteriopathy

49
Q

What can a D-Dimer test be used for
(5)

A

Rules out the presence of a thrombus

Rules out deep vein thrombosis

Rules out pulmonary embolism

Used to determine if further testing is necessary to help diagnose diseases and conditions that cause hypercoagulability

A D-dimer level may be used to help diagnose disseminated intravascular coagulation (DIC) and to monitor the effectiveness of DIC treatment

50
Q

What is deep vein thrombosis
(6)

A

Clot in the lower limbs

Pains in deep veins at the back of the calf

Oedema of the limbs

Pulmonary embolism

Platelets and fibrin

Jelly like mass of fibrin and red cells that may detach and form an embolism

51
Q

What is a pulmonary embolism
(9)

A

Clot that gets stuck in the pulmonary circulation

Most occur as a result of a DVT

Clot travels via leg veins to lung

Chest pain

Breathlessness

Cold clammy skin

Tachycardia

Hypotension

A large embolus can be immediately fatal

52
Q

What is disseminated intravascular coagulation?
(8)

A

Excessive and widespread activation of coagulation

Consumption of coagulation factors and inhibitors

Activation of the fibrinolytic system and an increase in fibrin degradation products

Systemic generation of thrombin and plasma activity

Formation of fibrin-platelet thrombus leading to microvascular ischaemia

Plasmin generation leads to the breakdown of the fibrin clot and the cleavage of fibrinogen

Loss of regulatory mechanisms

Defibrination and haemorrhagic diathesis (rarely associated with thrombosis)

53
Q

What might cause DIC?
(3)

A

Labour
Malignancy
infection

54
Q

What might cause acute DIC

A

Infection
Malignancy
Liver disease
Obstetrics
Trauma
Burns
Haemolytic reactions
Massive transfusion
Prosthetic devices

55
Q

What might cause chronic DIC
(8)

A

Malignancy
Obstetrics
Myeloproliferative diseases
PNH
Vascular disease
Myocardial infarction
Inflammatory disease

56
Q

How does DIC lead to end-organ damage?
(7)

A

Impaired blood flow caused by microvascular thrombosis

Ischemia reperfusion injury

Systemic inflammatory response syndrome

Multiple organ dysfunction syndrome

Kidneys-renal damage seen in 25% of DIC cases in one series

Liver - hepatic dysfunction in 19%

Lungs - respiratory dysfunction in 16%

57
Q

What are some laboratory features of DIC

A

PT APTT
Fibrinogen
D-Dimers
Thrombin Time
Platelet count
Blood film: Signs of haemolysis (schistocytes)

2.2 Haematology (38 decks)

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