Lecture 9 Flashcards Preview

Mlab121 > Lecture 9 > Flashcards

Flashcards in Lecture 9 Deck (18)
Loading flashcards...
1

Bleeding Time

--- Standard puncture made and blood blotted by filter paper to prevent external clotting
--- Start stop watch when puncture made. Record time at which bleeding stops
--- Test evaluates platelet function, capillary integrity and clotting factors

2

Duke Method:

Standard puncture to the ear lobe made by lancet
NR 1-3 minutes

3

Ivy Method:

Blood Pressure Cuff on the arm inflated to 40 mm Hg;
-- Standard puncture on forearm 1mm wide and 3 mm deep
NR -- 1-9 minutes
Panic Value -- > 12 minutes

4

QC for bleeding time test

Do not touch incision when blotting blood droplets
-- Record if patient has used aspirin in past 2 weeks

Lesson 3-3 review questions 3, 7

5

Prothrombin time , PT

Reagent: Thromboplastin (activates factor VII) (tissue factor III) and Ca++,
Sample and specimen are equilibrated for 5 minutes at 37ºC
Reagent is added to plasma and time to form a clot is measured
Tests extrinsic pathway (III -> (require Ca++)VII) & common pathway (-> X-> (require Ca++)V-> II-> I)
PT increased by deficiency of factors VII, X, V, II (prothrombin) and I (fibrinogen)
Used to monitor oral anticoagulant therapy (Coumadin)

6

Manual method Prothrombin time , PT

tilt tube method: mix plasma and reagent and tilt tubes; examine visually for clot to form

7

Automated method: Prothrombin time , PT

instrument monitors tube for change in optical density or electrical resistance

8

Specimen Prothrombin time , PT

citrated plasma; first tube drawn
centrifuge 15 min at 3000 rpm, separate plasma and refrigerate; freeze plasma if not tested within 4 hours

9

Results: - PT

PT, in sec, is converted to an International Normalized Ratio (INR)
INR = (PT patient / PT m¬ean normal) ISI, = PT RatioISI
ISI, International Sensitivity Index: specific to thromboplastin used

10

Ranges - PT and INR

Normal Range: PT = 10-14 sec
INR = 1
Therapeutic Range: PT = 16-18 sec
INR = 2-3
Panic Value: PT > 25 sec
INR> 4
Lesson 3-4 review questions 2, 4, 5, 8, 9

11

(Activated) Partial Thromboplastin Time, APTT or PTT

two reagents (1) cephaloplasmin with contact activator and (2) CaCl2 both reagents and specimen are equilibrated for 5 minutes at 37ºC cephaloplasmin is added to specimen and factor XII is activated after 3 minutes, CaCl2 is added to complete the clotting cascade tests intrinsic pathway XII->XI->(require Ca++)IX->(require Ca++)VIII and common->X->(require Ca++)V->II->I
Used to monitor intravenous anticoagulant therapy (Heparin) Specimen same as Pt

12

Ranges - PTT

Normal Range PTT = 25-35 sec
Therapeutic Range PTT = 1.5 to 2 x normal control
Panic Value PTT > 60 -100 sec

Lesson 3-5 review questions 2, 6, 8

13


Clotting Time
Lee and White method

stop watch started as whole blood taken by syringe and 1 mL aliquots dispensed into 3 tubes in 37ºC water bath. at 3 minutes, tubes tilted at 30 sec intervals and time of clotting is recorded NR 4 – 10 min

14

Activated Clotting Time, ACT

whole blood is drawn by venipuncture (red top) or finger pick; first tube of blood or first droplet from finger pick is discarded

15

POCT - Clotting

blood in dispensed into prewarmed tube or cuvette coated with an activator and inserted into instrument
clotting formation is detected by LED
NR = 90 – 150 sec
Therapeutic range =150-190 sec

16

Clot Retraction

red top tube taken and immediately placed into 37ºC water bath
tube is examined at 1, 2, 4, and 24 hours for clot retraction (clot pulls away from walls of tube)
clot volume expressed as % of total blood sample
NR 40-60%

17

Capillary Fragility, Tourniquet Test

blood pressure cuff is inflated with enough pressure to stop the venous return of blood (80-100 mm Hg)
result: capillary rupture and form peticchiae
after 5 minutes, peticchiae counted in a 3 cm circle
increased in DIC, Vit C deficiency, Vit K deficiency, clotting factor deficiency
NR 0 to 10 peticchiae
Pos test >11, indicates capillary weakness or platelet deficiency

18

Platelet function tests

platelet adhesiveness special order
platelet aggregation special order
Lesson 3-6 review questions 2, 6, 8