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Flashcards in coagulation in the lab Deck (18)
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1
Q

APTT prolonged but normal PT

A

intrinsic pathway

factor deficiency

  • VIII
  • XI
  • IX
  • XII
2
Q

prolonged PT but normal APTT

A

extrinsic pathway

factor deficiency most likely VII

  • could also be X, V, I, II
3
Q

both APTT and PT prolonged

A
  • deficiencies of factor II, V, X and I

multiple factor deficiencies

4
Q

TCT prolonged

A
  • deficiency of fibrinogen

- thrombin inhibitor (heparin or dabigatran)

5
Q

what factors are of concern if APTT is prolonged

A

VIII

IX

XI

XII

6
Q

mechanism of APTT testing

A
  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
7
Q

mixing studies

A

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

8
Q

causes of prolonged APTT

A

lupus anticoagulant

heparin

dabigatran

9
Q

describe lupus anticoagulant

A
  • is the most common cause of prolonged APTT
  • plasma antibodies interfere with phospholipid in APTT
  • does not cause bleeding
10
Q

describe heparin

A
  • up-regulates antithrombin therefore works as an anticoagulant
  • prolonged 1+1 corrects with protamine
11
Q

describe dabigatran

A
  • is a direct thrombin inhibitor

- prolonged 1+1 doesn’t correct with protamine

12
Q

describe factor inhibitors

A

autoimmune antibodies against clotting factor
- usually VIII

associated with bleeding and bruising

13
Q

describe the prothrombin time test

A
  • 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

14
Q

describe thrombin clotting time

A
  • thrombin added to plasma: which converts fibrinogen to fibrin
  • will be prolonged for heparin and dabigatran
    - protamine to differentiate
15
Q

other test to assess coagulation

A
  • single factor assays
  • whole blood clotting tests
  • platelet function assay
  • D-dimer (fragments of broken down fibrin)
16
Q

describes warfarin use and effect

A
  • used in AF, venous thromboembolism and other thrombotic disorders
  • inhibits recycling of vitamin K -> less coagulation
  • APTT and PT prolonged
  • monitor with INR
17
Q

describe haemophilia and its types

A

gives spontaneous joint and soft tissue bleeds

A = VIII deficiency
B = IX deficiency
18
Q

how do you test for haemophilia

A

prolonged APTT normal PR

single factor assays

genetic analysis