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Mlab121 > Lecture 8 > Flashcards

Lecture 8 Flashcards

1
Q

Haemostasis:

A

process of stopping loss of blood from blood vessels

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2
Q

Steps in Haemostasis:

A
  1. vasoconstriction: blood vessels narrow
  2. platelet activation: adhesion + aggregation (platelet plug formation)
    • Initiated by damaged or irregular blood vessels
    • Adhesion- Platelets adhere to damaged blood vessel
    • Aggregation- stick to each other to form a plug
  3. clotting cascade: intrinsic + extrinsic pathways (blood clotting)
  4. Fibrinolysis breakdown of fibrin initiated by the conversion of plasminogen to plasmin - LOOK AT LECTURE
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3
Q

APTT PATHWAY…………Intrinsic

A

• each activated factor activates the next in the series)
Initiated by contact with surface of blood vessel lining factor XII (12) is activated followed by (XI) 11 then (IX)9 using Ca then (VIII)8 using Ca and PF3 (platelet factor 3)
Contains factor XII, XI, IX, VIlI
Calcium is also needed for the activation

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4
Q

PT PATHWAY……Extrinsic

A

Thromboplastin (factor III) (comes from the skin) is released from damaged blood vessels and activates the next factor
Contains tissue factor and factor VII (7) using calcium

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5
Q

Common pathway

A

Check the lecture
Intrinsic and Extrinsic activates factor X (in common pathway)
Factors circulate in inactive forms until they are activated.

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6
Q

Stable Fibrin Clot

A

Fibrinogen (I) Fibrin (monomer) Fibrin (polymer) Stable fibrin clot

hemophiliacs cant clot

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7
Q

Problems in haemostatis:

A

insufficient or delayed clotting

intravascular clotting

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8
Q

intravascular clotting

A

thrombus (clot on vessel wall) can break off and become an embolus which travels through the blood
clot can lodge in the brain (stroke), heart (cardiac infarction), lung (pulmonary embolism), calves (deep vein thrombosis or phlebitis - when people are in a plane sitting)

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9
Q

Disorders of Haemostasis

Inherited Disorders:

A

Common Haemophilia A- factor VIII and VII:C deficiency – x chromosome defect (mostly men have disease and women are mostly carriers)
Haemophilia B- factor IX deficiency (Christmas disease) – x chromosome defect
Haemophilia C- factor XI deficiency chromosome 4 defect
Von Wildebrand’s disease- defect of platelets, platelet do not aggregate and do not activate factor VIII (proconvertin) – epistaxis (nose bleed symptoms) autosomal inherited by both men and women

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10
Q

Acquired Disorders

A
  • Vitamin K deficiency (clotting factors II- Prothrombin , VII-Proconvertin , IX- Christmas factor , X- Stuart Power Factor)
  • Disseminated Intravascular Coagulation (DIC):most often due to infection extra bleeding because of injury- thrombosis or bleeding
  • Heparin – inhibits thrombin activation and factor X-
  • Coumadin (warfarin) (anticoagulant – thrombosis) – acts to decrease Vit K dependent factors to allow for clotting
  • Aspirin – prevents platelets from making PF3
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11
Q

Coagulation Tests

Bleeding Time:

A

Test analyzes how quickly small blood vessels in your skin close up and stop bleeding.
Test evaluates platelet function, capillary integrity and clotting factors

Method:
• Standard puncture made and blood blotted by filter paper to prevent external clotting.
Platelet count of <50- may prolong the bleeding time

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12
Q

Miekle Modified Ivy Method –Bleeding Time Test (Done by technologists)

A
  • blood pressure cuff on patient forearm inflated to 40 mm Hg
  • standard puncture on forearm by template device (2 incisions 5mm wide and 1 mm deep)
  • Template device (Simplate or Surgicut) retractable blade
  • Start stop watch when puncture made
  • Record time at which bleeding stops

NR 1-9 minutes
Critical Value > 12 min

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13
Q

Bleeding Time Test QC

A
  • Do not touch incision when blotting blood droplets
  • Record if patient has used aspirin in past 2 weeks (platelet survival is 10 -14 days)
  • Proper PPE
  • Follow Standard Precautions
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14
Q

Prothrombin Time Test- PT

A
  • Used to monitor oral anticoagulant therapy (Coumadin) - common blood thinner - inactivates factor 7 so patient does not clot easy- too much bleed out not enough too many clots
  • Specimen citrated plasma (blue top tube)
  • Need Platelet Poor Plasma–Centrifuge 15 min at 3000 rpm, separate plasma and refrigerate; freeze plasma if not tested within 4 hours
  • Reagent ( thromboplastin)= (tissue factor III-phospholipid) and CaCl++
  • PPP plasma and thromboplastin are incubated for 5 minutes at 37ºC

Incubate no longer than 10mins-why?
• Factor VIII deteriorates
• Reagent evapourates
• Reagent is added to plasma and time to form a clot is measured
• Perform in duplicate: PT result must be within 10%
Tests extrinsic pathway III -> (needs Ca) VII & common pathway-> X ->(needs Ca) V-> II-> I
PT increased by deficiency of factors VII, X, V, II (prothrombin) and I (fibrinogen)
PT increased in liver disease

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15
Q

PT- Manual method: Tilt tube

A
  • mix plasma and reagent
  • tilt tubes
  • examine visually for clot to form
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16
Q

Automated method

A
  • The instrument monitors tube for change in optical density or electrical resistance
  • End point fibrin clot
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17
Q

Principle of clot detection: SEMI –AUTOMATED

A
  • The increase of viscosity is measured through the motion of a stainless steel ball
  • Constant pendulum swings of the ball are created by an electromagnetic field that is applied alternately on opposite sides of the cuvette by two independent driving coils.
  • However as soon as the plasma starts to clot (as of coagulation process being initiated by addition of the clot starting reagent), the viscosity of the plasma starts to increase, and this change in plasma viscosity affects ball movement, slowing it down.
18
Q

Prothrombin Time Test

A

Results: PT, in sec, is converted to an International Normalized Ratio (INR)
• INR (international normalized ratio) is a way of standardizing the results of prothrombin time tests, regardless of the testing method.
• This helps the doctor to understand results in the same way even when they come from different labs and different test methods.
• Using the INR system, treatment with blood-thinning medicine (anticoagulant therapy) will be standardized.
• In some labs, only the INR is reported and the PT is not reported
• ISI, International Sensitivity Index: specific to thromboplastin used (usually 1.0)

19
Q

Ranges for PT and INR

A

Normal Range PT = 10-14 sec
INR = 0.8-1
Therapeutic Range PT = 16-18 sec
INR = 2-3
Critical Value PT > 25 sec
INR> 4

An abnormal prothrombin time is often caused by liver disease or by treatment with blood thinners.
Some Drugs that can affect the PT result: Aspirin, Vit K supplement, antibiotics and the birth control pill

20
Q

(Activated) Partial Thromboplastin Time, APTT or PTT

A

• Specimen same as PT (3.2% Na citrate)
Two reagents
(1) cephaloplasmin (phospholipid) with contact activator and (2) CaCl2

Both reagents and specimen are equilibrated for 5 minutes at 37ºC
Cephaloplasmin (phospholipid) is added to specimen and factor XII is activated after 3 minutes
CaCl2 is added to complete the clotting cascade

PTT is the most useful routine screening tests for the intrinsic pathway and common pathways
Intrinsic XII->XI->(require Ca++)IX->(require Ca++)VIII and common->X-> (require Ca++)V->II->I
Used to monitor intravenous anticoagulant therapy (Heparin)

21
Q

QC (Activated) Partial Thromboplastin Time, APTT or PTT

A

Manual method
Duplicate results:
<40 sec: must be within ±2 seconds or repeat
>40 sec: must be within ±3 seconds or repeat

22
Q

Sources of Error/Troubleshooting:(Activated) Partial Thromboplastin Time, APTT or PTT

  1. Associated with specimen
A

a. Order of draw
b. Inappropriate ratio of anticoagulant to blood
c. Clotted, hemolyzed or lipemic samples
d. <10,000 platelets x10^/L
e. Delay in testing or processing
f. Inappropriate storage

23
Q

Sources of Error/Troubleshooting:(Activated) Partial Thromboplastin Time, APTT or PTT

  1. Associated with storage
A

a. Incorrect preparation of reagents
b. Failure to properly store reagents
c. Use of reagents beyond reconstituted stability time or expiration date
d. Contaminated reagents

24
Q

Sources of Error/Troubleshooting:(Activated) Partial Thromboplastin Time, APTT or PTT

Associated with procedure

A

a. Incorrect temperature
b. Incorrect incubation times (↑ incubation time=↓PTT due to contact activation and > 5min heating will result in loss of heat-labile factor V)
c. Incorrect volumes of sample, reagents or both

Quality Control: Normal and Abnormal Control plasma must be run every 8 hours

25
Q

PTT normal range

A

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

26
Q

Interpretation of PT and PTT Results
PT result - prolonged
PTT normal

A

Liver disease, decreased vitamin K, decreased or defective factor VII

27
Q

Interpretation of PT and PTT Results
PT result - normal
PTT - prolonged

A

Decreased or defective factor VIII, IX, or XI, von Willebrand disease, or lupus anticoagulant present

28
Q

Interpretation of PT and PTT Results
PT result - prolonged
PTT - prolonged

A

Decreased or defective factor I, II, V or X, severe liver disease, disseminated intravascular coagulation (DIC)

29
Q

Interpretation of PT and PTT Results
PT result - normal
PTT - normal

A

May indicate normal haemostasis; however PT and PTT can be normal in conditions such as mild deficiencies in other factors and mild form of von Willebrand disease. Further testing may be required to diagnose these conditions.

30
Q

Quality Assurance for Point of Care Test Operators

A
  • Training for all POCT operators who perform Point-of-Care Testing (POCT)
  • To meet accreditation standards POCT operators must be knowledgeable about the types of Point-of-Care Testing (POCT) they are responsible for
  • POCT operators are accountable to complete training
  • Training can be In house or online
  • POCT operators have documented evidence of training
  • POCT operators are qualified to perform their responsibilities and perform tests according to the manufacturer’s instructions to obtain accurate and reliable results.
  • A Policies & Procedures Manual is available to POCT operators
  • Assess POCT operator competency as per SOP and accreditation
31
Q

POCT Tests

A
  • blood glucose
  • urine dipsticks
  • blood gases
  • chemistry
  • hematology
  • coagulation
  • cardiac markers
  • Pregnancy tests
32
Q

Criteria for Result Reporting POCT

A
  • Run QC for accuracy and precision
  • Test results are reported only when all performance specifications for a test are within QC acceptable limits
  • Remedial actions are taken and documented when required
  • When instrument problems are detected, all patient results obtained since the last acceptable quality control run are evaluated to determine if they have been adversely affected
  • Reported result include pertinent information required for interpretation
  • Patient specimen is analyzed only after meter function checks are OK
  • Calibrates the system for each new box of test strips
33
Q

CoaguChek XS System-POC

A
  • PT/INR in one minute
  • Finger prick or venous sample (minimum 8ul)
  • Test strip has reagent and code
  • A blood drop is applied within 15 sec of collection
  • The meter starts the test and the blood mixes with the ingredients on the test strip
  • When the meter determines that the blood has clotted, it stops the measurement and calculates the result.
  • Results are stored in the meter
  • Battery operated

Disadvantages - its just one test at a time with only one drop of blood

34
Q

Daily check of POCT meter

A
  • Check expiry date of strips
  • Place the meter on a flat surface, free of vibrations
  • Ensure that internal QC results are acceptable during testing.
  • Follow the policies and procedures for collecting and handling samples, testing patient samples, and reporting test results.
  • Report or log patient tests result
  • Clean and disinfect POC system
35
Q

Monthly check of POCT meter

A

• Review QA Checklist. Include all the actions associated with the erroneous result

36
Q

Every 3- 6 Months check of POCT meter

A

• Perform an external evaluation of accuracy, such as split sample testing or have two operators test the same patient and compare results.

37
Q

Pre-analytic Errors

A
  • Patient ID
  • Sample collection
  • Test Ordering
  • Incomplete Requisition
  • Leaving the test strip exposed to light for extended time
  • Selecting the correct site
  • Specimen accessing
38
Q

How clot occurs

A

when blood vessel rips there is exposed collagen on the wall. The platelets stick to the collagen - adhesion - vWf and glycoprotein - they are disc shaped right now

  • Then change to spikey shaped and stick to each other aggregation to form plug- need Ca. Coag factors are made in the liver . Release factor V and platelet factor
  • Esstentially youre converting prothrombin (2) to thrombin and then fibrinogen (1) to fibrin
  • So now blood is moving past the formed clot causing lots of plasminogen (inactive plasmin). THe skin cells around the clot release tPA which converts the bound plasminogen to plasmin.
  • The plasmin then breaks down the clot making FDPs and Ddimers
39
Q

Why is APTT done

A

The activated partial thromboplastin time (called APTT or aPTT) is a coagulation test used to monitor low-dose heparin therapy and to screen for function of the intrinsic and common pathways of hemostasis

All of the factors required to activate the intrinsic pathway are present in the circulating blood.

40
Q

The extrinsic pathway

A

The extrinsic pathway is so named because one of the coagulation factors involved, factor III, is not present in circulating blood.
The hemostasis pathway is activated when damage occurs to blood vessel endothelium or to tissue. The extrinsic pathway is activated by tissue thromboplastin (factor III) in the presence of calcium ions. Factor X, a proenzyme, is converted to the enzyme Xa, which in turn converts prothrombin to the enzyme thrombin

41
Q

The prothrombin time

A

The prothrombin time or protime, one of the most frequently performed coagulation tests, evaluates the function of the extrinsic and common pathways of hemostasis. The major use of the prothrombin time is to monitor warfarin (Coumadin) anticoagulant therapy; the test is also used as a presurgery coagulation screening test. Warfarin is a vitamin K antagonist, which means it blocks the action of vitamin K.

Mlab121 (14 decks)

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