Coagulation

Question 1

Why is the extrinsic pathway called extrinsic?

Answer 1

TF, which starts the pathway, is from extravascular cells

Question 2

When measuring APTT, factor 12 activation by glass / Kaolin / ellagic acid is required to start coagulation. Does that mean a patient with factor 12 deficiency has a tendency to bleed? (2)

Answer 2

No, the coagulation property in vitro won’t exist in vivo. In vivo, it converts plasminogen to plasma, so factor 12 deficiency (as well as prekallikrein deficiency) causes thrombosis instead of bleeding.
Its relationship with thrombosis is inconclusive.

Question 3

Why is using EDTA & Heparin for PT/APTT tests a bad idea? (2)

Answer 3

Heparin anticoagulant effect is from activation of antithrombin 3
EDTA also inhibit thrombin

Question 4

Why is the citrate to blood ratio 1:9 for PT/APTT tests? (1)

Answer 4

Ca2+ are all removed in this concentration of citrate, this ensure no coagulation takes place before the test

Question 5

Explain the use of formula (0.00185)(V)(100–H) = C. (1)

Answer 5

In case of extreme high / low HCT, heparin volume (C) can be adjusted based on blood volume (V) & HCT (H)

Question 6

What is inside a PT reagent? (2)

Answer 6

Thromboplastin (PL + TF) & Ca2+

Question 7

Can we measure factor 13 using PT/APTT? (1) What is the function of factor 13 in vivo? (1)

Answer 7

No, factor 13 cross-linked fibrin to stabilize it in vivo

Question 8

Fibrinogen is measured by Clauss method, is this method the same method for TT? (2)

Answer 8

Clauss’ method uses diluted plasma. In excess thrombin, more fibrinogen means shorter TT

Question 9

Name vitamin K dependent coagulation factors (4) How vitamin K activates them? (1) Will PT/APTT levels be affected if a patient is vitamin K deficient? (1)

Answer 9

2,7,9,10
vitamin K activate factors by carboxylation of glutamate residues
Both PT & APTT are affected as 10,2 are common pathway’s factors

Question 10

How does FDP differ from D-dimer?(1)

Answer 10

FDP measures degradation products of both fibrinogen & fibrin
D-dimer measures degradation of cross-linked fibrin

Question 11

Name the endogenous & exogenous activator of plasminogen (2)

Answer 11

tPa
streptokinase

Question 12

Name 1 inhibitor of fibrinolysis (1)

Answer 12

alpha2 antiplasmin

Question 13

Does high D-dimer mean patients have the DIC? (1) Does low D-dimer mean patients don’t have DIC? (1)

Answer 13

No, Yes.
D-dimer is sensitive but not specific for DIC

Question 14

A sample ordering PT & APTT collected 6 hours ago, you should? (2)

Answer 14

Cancel both as sample delay >4h, if single PT test is ordered, the test can be performed as capped PT is stable for 24h

Question 15

Which factors are activated by factor 2 in the PT test? (2)

Answer 15

factor 5,8

Question 16

Name the substrate used in chromogenic factor assay

Answer 16

p-nitroaniline (pNa), at 405 nm

Question 17

Why do we use INR instead of PT for result interpretation?(1) Why is ISI different for PT reagents made by different companies? (1)

Answer 17

Monitor warfarin
The result is normalized with population PT
ISI accounts for differences in Thromboplastin composition
Therefore, INR is universal & comparable across different labs

Question 18

Name 3 conditions causing high D-dimer (3)

Answer 18

DIC, thrombolytic therapy, thrombosis (PE)