Haematology JC047: Abnormal Bleeding After Tooth Extraction: Bleeding Tendency, Thrombocytopenia

Question 1

3 components of Haemostatic system

Answer 1

1. Blood vessels
2. Platelets
3. Coagulation / Clotting factors

**3 phases after injury to blood vessels:
1. Vasoconstriction (limit bloodflow to injured blood vessel)
2. Platelet activation —> Platelet aggregates / **plugs formation
3. Activation of coagulation —> Formation of ***Fibrin clot

Question 2

Phases of platelet activation

Answer 2

Damage to endothelium
—> Exposure of **subendothelial tissue
—> Circulating platelets (guided by **vWF) come into contact with subendothelial tissue (esp. collagen)
—> Platelet activation
—> Activation of intracellular signalling pathway within platelet
—> **Shape change of platelet + **Degranulation (containing agonists of platelet activation: ADP, Serotonin, Ca, Fibrinogen, Factor 5, 11)
—> More platelet activation (+ve feedback)
—> Platelet aggregation + Platelet adhesion

Question 3

Main agonists of platelet activation

Answer 3

1. ***ADP (Adenosine diphosphate) —> content of platelet granules
2. Thrombin
3. Collagen (present in huge amount in subendothelial tissue)
4. Adrenaline
5. ***Serotonin —> content of platelet granules
6. ***Calcium ionophores —> content of platelet granules

Question 4

Platelet degranulation

Answer 4

2 types of platelet granules:
1. Alpha granules
- **Fibrinogen
- **vWF
- Factor 5
- Factor 11
- HMWK (High molecular weight kininogen)

2. Dense granules (electron dense under EM ∵ presence of Ca)
   - **ADP
   - ATP
   - **Serotonin
   - ***Calcium

Question 5

Platelet adhesion + Platelet aggregation

Answer 5

1. Platelet adhesion
   - GP1a/2a + GP6 —> adhere to Subendothelial collagen
   - GP1b/9/5 complex —> adhere to Subendothelial collagen indirectly via binding to **vWF
   - GP2b/3a receptor —> adhere to Subendothelial collagen indirectly via binding to **Fibrinogen
2. Platelet aggregation
   - GP2b/3a receptor —> adhere to Fibrinogen —> adhere to other GP2b/3a of other platelets

Question 6

Clotting factors

Answer 6

Role of clotting factors in haemostasis: Formation of Fibrin clot via Activation of coagulation cascade

Activation of coagulation cascade
1. Initiation phase:
- Activation of Factor 7 by Tissue factor (released / exposed due to tissue injury) —> Factor 7a
—> **Factor 10 —(7a)—> Factor 10a
—> Prothrombin —(10a + 5a)—> Thrombin (*very slow process + very small amount)
—> Fibrinogen —(Thrombin)—> Fibrin

2. Amplification phase:
   - Factor 9 —(7a + 11a)—> Factor 9a
   - **Factor 8, 11 —(Thrombin (generated in initiation phase))—> Factor 8a, 11a
   —> Factor 10 — (9a + 8a)—> Factor 10a
   —> Prothrombin —(10a + 5a)—> Thrombin (**large amount)
   —> Fibrinogen —(Thrombin)—> Fibrin

Formation of fibrin clot: requires large amount of Thrombin

Principal steps in activation of coagulation:
1. Factor 7 is the key factor involved
2. Tissue factor is a principal factor involved in activation of Factor 7
3. Factor 7a activate Factor 10 (Initiation phase)
4. Factor 10a converts Prothrombin to Thrombin (very little amount)
5. Thrombin activates **Platelets, **Factor 8, **Factor 5, **Factor 11

6. Factor 7a activate Factor 9 (Amplification phase)
7. Factor 9a + 8a generate ***large amount of Thrombin via 10a + 5a
8. Thrombin converts Fibrinogen to Fibrin —> Insoluble cross-linked Fibrin clot (with help of Factor 13)
9. Thrombin is the central molecular involved in blood coagulation

Question 7

Coagulation assays to evaluate clotting system in vivo

Answer 7

Prothrombin time (PT)
- evaluate Extrinsic pathway (Factor 7 + Tissue factor) + Common pathway (Factor 1, 2, 5, 10)
- ***Isolated ↑ PT —> Factor 7 deficiency

Activated partial thromboplastin time (aPTT)
- evaluate Intrinsic pathway (Factor 9 + Factor 8) + Common pathway (Factor 1, 2, 5, 10)
- Factor 12 deficiency will NOT cause bleeding
- ***Isolated ↑ aPTT —> Factor 9, 8 deficiency

Question 8

Haemostatic disorders

Answer 8

1. Platelet defects
   - Quantitative: Thrombocytopenia
   —> ↓ Production: **BM disease
   —> ↑ Destruction: **Immune-mediated (e.g. **ITP, drugs), **Hypersplenism, Cirrhosis, Portal hypertension

• Qualitative: Platelet function disorder
  —> ***Drugs (most common): Aspirin, NSAIDs
  —> Acquired: Renal failure
  —> Inherited: Very uncommon e.g. Bernard-Soulier syndrome (GP1b deficiency on surface)

2. Coagulation defects
   - Acquired coagulation disorders
   —> **Liver disease (most common): **Vit K deficiency in Jaundice (∵ Cholestasis ↓ Vit K absorption) (Prothrombin, Factor 7, 9, 10: Vit K dependent clotting factors), **↓ production of clotting factors in Liver failure
   —> **Drugs: Anticoagulants (Vit K antagonist, NOAC)

• Inherited coagulation disorders
  —> **von Willebrand disease (most common) (vWD: deficiency in quantity / quality of vWF)
  —> **Haemophilias (A, B, others)

Question 9

Patterns of bleeding: Platelet vs Coagulation disorders

Answer 9

Clinical features:
Platelet disorders:
1. SC bleeding
- **Petechiae / Purpura / Ecchymosis
2. **Mucosal bleeding
3. Intracranial bleeding
4. ***Retinal haemorrhage
5. NO Intramuscular + Intraarticular bleeding

Coagulation disorders:
1. SC bleeding
- **Ecchymosis (usually no Petechiae, Purpura)
2. NO Mucosal bleeding
3. Intracranial bleeding
4. NO Retinal haemorrhage
5. **Intramuscular + Intraarticular bleeding (Haemarthrosis)

Question 10

Laboratory tests of Haemostasis

Answer 10

1. Skin bleeding time (obsolete)
2. ***Platelet count (very useful)
3. Platelet function test (not routine)
4. Clotting time (obsolete)
5. ***PT (very useful)
6. ***aPTT (very useful)
7. Other tests (e.g. specific factor assay) (optional)

Question 11

***Results of Coagulation tests in various disorders

Answer 11

1. Vit K deficiency (i.e. Factor 2, 7, 9, 10 deficiency) (Jaundice):
   - PT: ↑ (∵ Factor 7 shortest t1/2, PT ↑ first seen)
   - aPTT: Normal
2. Warfarin (Vit K antagonist)
   - PT: ↑
   - aPTT: Normal (↑ if overdose)
3. Liver disease
   - PT: ↑
   - aPTT: Normal (↑ if fulminant liver failure ∵ other factors also ↓)
4. Unfractionated Heparin (not LMWH)
   - PT: Normal
   - aPTT: ↑
5. Haemophilia A / B (Factor 8 / 9 deficiency respectively)
   - PT: Normal
   - aPTT: ↑
6. Platelet disorder
   - PT: Normal
   - aPTT: Normal

Question 12

Treatment options in Haemostatic disorders

Answer 12

Platelet disorders (Quantitative / Qualitative)
1. **Platelet transfusion
2. **Steroid / Immunosuppressants (for Immune-mediated e.g. ITP)
3. **IVIG (ITP: rapid ↑ Plt count)
4. Thrombopoietin receptor agonists e.g. Eltrombopag, Romiplostim (for **refractory ITP)

Coagulation disorders (depends on cause)
1. **Vit K (for Jaundice / Liver disease)
2. **Specific factors / Factor concentrates (for Haemophilia, vWD) (NO vWF concentrate in HK, use Intermediate Purity Factor 8 concentrate (also contain vWF)
3. **Fresh frozen plasma (contain all clotting factors, for Coagulopathy due to liver failure, Warfarin overdose)
4. **DDAVP (Desmopressin) (stimulate release of **vWF, **Factor 8 from platelet / endothelium, for ***Mild Haemophilia A / vWD)

Question 13

Low platelet count: Approach

Answer 13

1. Repeat + Confirm (citrate blood if needed)
   (∵ might be due to EDTA-dependent pseudothrombocytopenia, patient may contain ***EDTA-dependent AutoAb against platelet —> underestimation of platelet count in machine —> blood smear / use citrate instead of EDTA)
2. Isolated thrombocytopenia / Pancytopenia (if along with Anaemia, Leukopenia)
   - Pancytopenia: indicate ***BM failure (↓ production)
3. Isolated thrombocytopenia
   - usually **↑ destruction (instead of ↓ production)
   —> **Chronic liver disease (cirrhosis, portal hypertension, hypersplenism)
   —> **ITP
   —> **Drug-induced (Rifampicin, Vancomycin, Penicillin (SpC Revision))
4. Assessment of bleeding risk
   - Absolute Plt count: **<20 (high spontaneous bleeding risk) —> Need to treat (otherwise **observe)
   - CNS bleeding risk: ***Fundoscopic examination (look for evidence of retinal haemorrhage)
5. Treatment
   - **Platelet infusion
   - **Steroid / IVIG (for ITP)

Question 14

Isolated prolonged PT: Approach

Answer 14

1. Repeat + Confirm
2. Assess whether patient is jaundiced (i.e. Obstructive jaundice)
3. Assess whether patient has a liver disease
4. Drug: Warfarin
5. Why obstructive jaundice?
6. Treatment
   - **Parenteral Vit K (replenish Vit K dependent clotting factors)
   - If Warfarin overdose: **Fresh frozen plasma / Vit K treatment

Question 15

Isolated prolonged aPTT: Approach

Answer 15

1. Repeat + Confirm
2. Commonest cause of prolonged aPTT is ***Heparin contamination (if blood taken from a catheter —> need to discard initial 5-10 ml of blood drawn)
3. Lupus anticoagulant (not associated with bleeding, associated with **thrombosis in vivo)
   - aPTT very sensitive to **deficiency of phospholipid (Lupus anticoagulant bind to phospholipid)
   - in vivo: Lupus anticoagulant causes ***damage to endothelium —> pro-thrombotic
4. Man
   - Haemophilia A / B (X-linked recessive)
   - vWD (type 1, 2: AD; type 3: AR)
5. Woman
   - vWD (type 1, 2: AD; type 3: AR)
6. Treatment
   - Haemophilia A / B, vWD
   —> **Factor concentrates (plasma derived / recombinant)
   —> **DDAVP for mild haemophilia

Question 16

Prolonged PT + aPTT

Answer 16

3 conditions:
- **Fulminant liver failure
- **DIC
- ***Thrombin inhibitor

1. Repeat + Confirm
2. Measure ***Fibrinogen concentration (for DIC)
3. Measure ***Platelet concentration (for DIC)
4. ***DIC (consumptive coagulopathy due to thrombosis in microvasculature causing consumption of all clotting factors): ↑ PT + ↑ aPTT + ↓ Fibrinogen + ↓ Platelet + RBC fragments (MAHA)
5. DIC with all these components a very uncommon clinical situation
6. Treatment of DIC
   - Replenish consumed coagulation factors with ***FFP
   - Reverse underlying causative factor