coagulation in the lab

Question 1

APTT prolonged but normal PT

Answer 1

intrinsic pathway

factor deficiency

• VIII
• XI
• IX
• XII

Question 2

prolonged PT but normal APTT

Answer 2

extrinsic pathway

factor deficiency most likely VII

• could also be X, V, I, II

Question 3

both APTT and PT prolonged

Answer 3

• deficiencies of factor II, V, X and I

multiple factor deficiencies

Question 4

TCT prolonged

Answer 4

• deficiency of fibrinogen

- thrombin inhibitor (heparin or dabigatran)

Question 5

what factors are of concern if APTT is prolonged

Answer 5

VIII

IX

XI

XII

Question 6

mechanism of APTT testing

Answer 6

1. venous blood collected into citrate
   
   • removes Ca2+ inhibiting clotting
2. spin sample down to collect plasma
3. add phospholipid and activator
4. then add Ca2+ to overcome citrate
5. measure length of time for clot to form

Question 7

mixing studies

Answer 7

1: 1 with normal plasma + incubation
- e.g. patient sample + normal sample

if sample correct to normal = factor deficiency

if sample does not correct = inhibitor present

Question 8

causes of prolonged APTT

Answer 8

lupus anticoagulant

heparin

dabigatran

Question 9

describe lupus anticoagulant

Answer 9

• is the most common cause of prolonged APTT
• plasma antibodies interfere with phospholipid in APTT
• does not cause bleeding

Question 10

describe heparin

Answer 10

• up-regulates antithrombin therefore works as an anticoagulant
• prolonged 1+1 corrects with protamine

Question 11

describe dabigatran

Answer 11

• is a direct thrombin inhibitor

- prolonged 1+1 doesn’t correct with protamine

Question 12

describe factor inhibitors

Answer 12

autoimmune antibodies against clotting factor
- usually VIII

associated with bleeding and bruising

Question 13

describe the prothrombin time test

Answer 13

• adding tissue factor to stimulate extrinsic pathway
• accesses vitamin K dependent factors
  e. g. VII, II, X

ratio = PT (patient) / PT (normal)
- should be 1

Question 14

describe thrombin clotting time

Answer 14

• thrombin added to plasma: which converts fibrinogen to fibrin
• will be prolonged for heparin and dabigatran
  - protamine to differentiate

Question 15

other test to assess coagulation

Answer 15

• single factor assays
• whole blood clotting tests
• platelet function assay
• D-dimer (fragments of broken down fibrin)

Question 16

describes warfarin use and effect

Answer 16

• used in AF, venous thromboembolism and other thrombotic disorders
• inhibits recycling of vitamin K -> less coagulation
• APTT and PT prolonged
• monitor with INR

Question 17

describe haemophilia and its types

Answer 17

gives spontaneous joint and soft tissue bleeds

A = VIII deficiency
B = IX deficiency

Question 18

how do you test for haemophilia

Answer 18

prolonged APTT normal PR

single factor assays

genetic analysis