Coagulation in the lab and bleeding disorders

Question 1

How the traditional coagulation pathway is different from what happens in the body

Answer 1

It dIntrinsic pathway doesn’t happen in people!! only in the lab
The two pathways join together in the middle to form the common pathway

Question 2

APTT

Answer 2

Activated partial thromboplastin time

• venous blood sample collected into citrate
• Citrate stops blood from clotting in the tube because it removes calcium (need for folding proteins) (chelation)
• Spin the sample down to collect the plasma
• Add phospholipid as an activator
• Add known amount of calcium to overcome the citrate
• Length of time to clot formation

Question 3

examples of contact factors

Answer 3

Kaolin
Silica
Ellagric

Question 4

Prothrombin time or ratio?

Answer 4

The prothrombin time (in seconds) is often covered to the prothrombin ratio
This standardises the test to account for different laboratory methods and different normal ranges for the prothrombin time
Prothrombin time (patient) / Prothrombin time (normal plasma, an average of heaps of different plasma samples)
The normal ratio is around 1.0 (plus or minus a small amount)

Question 5

Explain the 1:1 mixing studies

Answer 5

1:1 mixing with normal plasma and intubation
Sample corrects to normal and remains normal = factor deficiency
Sample doesn’t fully correct (anything above the normal range) then an INHIBITOR is present

Because… IF a person has no closing factor whatsoever their assay will be prolonged, if they have 40-50% of the factor the APTT will almost be normal. So if I add 50% normal plasma to that childs sample, even if he has none of a particular factor e.g. no factor VIII, if you add normal plasma it will supply 50% of clotting factors and APTT will be normal

Question 6

The types of inhibitors in coagulation

Answer 6

Antithrombin, protein C and protein S are called inhibitors as they shut down coagulation
They do not affect the APTT
Different inhibitors affect the APTT

Question 7

The lupus anticoagulant

Answer 7

Prolongs the APTT
2 different scenarios
- anti-phospholipid syndrome, where you get excess clotting
- Present transiently in patients who are very unwell, e.g. marked inflammation or infected patients in hospitals
DO NOT CAUSE BLEEDING
–> antibodies involved interfere with phospholipid in APTT assay, because we only supply a little phospholipid to trigger clotting in the assay. In the body theres masses of phospholipid, so not restricted

Question 8

Autoimmune antibodies against a clotting factor - usually VIII

Answer 8

RARE
Associated with bleeding including bone bruising
Can be life threatening
Causes acquired haemophilia

Question 9

Heparin

Answer 9

Also causes prolonged 1+1
confirmed by addition of protamine
Anticoagulant that works as an inhibitor by up regulating antithrombin –> blocks activated thrombin, therefore adding normal plasma doesn’t over come the effect of the normal inhibitor
Biological glycosaminoglycan chains
Natural glycosamino glycans activate antithrombin in vivo

Question 10

Common uses of heparin to be aware of when taking a blood sample

Answer 10

To stop central lines from clotting is not used for a while

Donttake blood sample from central line unless you draw a lot of blood off first

Question 11

Dabigatran

Answer 11

Oral, to treat venous thrombosis and atrial fibrillation
Direct inhibitor of thrombin
Prolonged 1:1 doesn’t correct with protamine, whereas heparin will

Question 12

APTT Prolonged, PT normal

Answer 12

deficiencies fo factors VIII, IX, XI, XII (intrinsic)

Question 13

PT prolonged, APTT normal

Answer 13

deficiency of factor VII (extrinsic)
occasional mild deficiencies of II, V, X, I
–> how can you get deficiencies of common pathway factors with normal APTT? Because APTT less sensitive than PT, PT prolonged if factor deficiency decreased by 40-50% whereas APTT needs big factor deficiency to be affected

Question 14

Causes of a prolonged TCT

Answer 14

• Deficiency of fibrinogen

- Thrombin inhibitor (e.g. dibigatran or heparin)

Question 15

Multiple factor deficiencies: most common scenario

Answer 15

Warfarin or Vit k deficincy (II, VII, IX, X)
Massive blood loss, loss of coagulation factors and dilution with fluids
DIC
- Widespread activation of coagulation causing thrombosis, followed by bleeding as clotting factors and platelets used up. Low fibrinogen often seen
- Liver disease: lack of production of coagulation factors and inhibitors (except VIII, as not made in the liver)

Question 16

What is the most sensitive test for liver disease?

Answer 16

prothrombin assay, because bit K dependant factors get used up first, issues with biliary cycle and Vit K deficiency common in liver disease

Question 17

what is the INR for?

Answer 17

= international normalised ratio.

To standardise Prothrombin ratio, PR, because all labs are different

Question 18

About warfarin

Answer 18

general name for several hydroxy-coumarin derivatives
Inhibits the recycling of vit K
Lack of carboxylated factors
Dose adjustments via the INR
Reversed by vit K (or more rapidly by replacing clotting factors in plasma products)
Used in atrial fibrillation, venous thromboembolism, other thrombotic disorders

Question 19

How to approach hereditary factor deficiencies

Answer 19

they're less common 
Usually a single factor is deficient 
First do a bleeding history 
Basic coagulation tests 
Depending on these, single factor assays

Question 20

Systemic effects of haemophilia

Answer 20

spontaneous joint bleeds 
- chronic athropathy 
- joint dysfunction 
- Deformity
- arthritis 
Soft tissue bleeds 
- Tissue damage 
- nerve damage 
- deformity

Question 21

Haemophilia A

Answer 21

factor VIII deficiency
most common hereditary disease with serious bleeding 
1 in 5000 live male births 
Inheritance is X-linked recessive 
mild, moderate, severe

Question 22

Haemophilia B

Answer 22

Deficiency of factor IX (christmas factor)
Inheritance is X linked recessive
Incidence: 1 in 30,000 live male births
clinical features identical to haemophilia A

Question 23

Haemophilia treatment

Answer 23

replace missing factor 
Recombinant in NZ 
Prophylaxis in children and teenagers when severe 
Normal lives and joint outcomes 
except patients who develop inhibitors

Question 24

How to test for haemophilia

Answer 24

prolonged APTT with normal PR
single factor assays
Genetic analysis
- sequencing of the factor VIII or IX gene
- Restriction fragment analysis in PCR in selected cases

Question 25

What else other than haemophilia can cause a low factor VIII level?

Answer 25

Patients who lack VW factor will not always but often lack factor VIII as well

Question 26

Describe VW factor

Answer 26

Plasma glycoprotein
Synthesised in megakaryocytes and endothelial cells
promotes platelet adhesion at vessel wall
Serves as a carrier for factor VIII
Complexes with factor VIII to stabilise and prevent degradation

Question 27

epidemiology of VW disease

Answer 27

Most common inherited bleeding disorder
Worldwide inheritance 1-3%
Autosomal dominant
Qualitative of quantitative abnormality of VWF

Question 28

Test for VW disease

Answer 28

Abnormal platelet function screen
Marginally prolonged APTT
Low factor VIII
Low level and function of VW factor with specific tests

Question 29

Symptoms of VW disease

Answer 29

Mucosal bleeding (lack of platelet tethering) 
- Epistaxis 
- Gum bleeds 
- GI blood loss 
Brusing 
Menorrhagia 
Postpartum or preoperative bleeding 
Autosomal family history 
Can be mild through to severe

Question 30

Factor XII deficiency??

Answer 30

Hereditary XII deficiency is common with no bleeding sequelae, but shows up in the lab test and corrects in the 1+1 test
We don’t need factor XII to clot, is why she has no bleeding history

Question 31

DIC mild vs severe complications

Answer 31

It can originate from and cause damage to the microvasculature which if sufficiently severe can cause organ dysfunction

Question 32

Causes of DIC

Answer 32

sepsis - lots of different bacteria e.g. meningicocal septicaemia –> purpuric rash
Malignancy
Organ damage e.g. pancreatitis
Trauma