MODULE 4: PRE-ANALYTICAL VARIABLES AND COAGULOMETRY Flashcards by pink popcorn

PRE-ANALYTICAL VARIABLES

Patient management (part of the physician)
Needle selection
Collection tubes
Venipuncture procedures
Sample transport and storage
Preparation of specimens based on tests to be performed

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Needle bore should be sufficient to prevent hemolysis and to
prevent the activation of ____ and ____

platelets and procoagulants

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Hemolysis, such as in traumatic venipuncture
■ There will be a _____platelets and coagulants

a premature activation

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Hemolysis has

shortened
coagulation test

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Adult with good veins :needle gauge and length

20 or 21 gauge, thin-walled, 1.0 or 1.25
inches long

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Child or adult with small,
fragile, or hardened veins :needle gauge and length

23-gauge, winged-needle set (butterfly
set); collect with small evacuated tubes or
syringe

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Transfer of blood from
syringe to tube

19-gauge safety transfer unit; slowly inject
through tube closure

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Sodium citrate Concentration:

0.105 to 0.109 M

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MW =

294.1 Daltons

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9:1 ratio

9 parts whole blood to 1 part anticoagulant

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○ Ratio of anticoagulant to whole blood: 1:9

■ 0.3 mL of anticoagulant + 2.7 mL of whole
blood

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Calculation of anticoagulant (to adjust) if Hct is >55% or >0.55L/L:

C= (1.85 X 10-3) (100-H) V

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What will happen if there will be increased volume of the RBCs
compared to the plasma or the anticoagulant?

the result of the coagulation test can be prolonged since
there will be less concentration of the plasma coagulation
factors because of the increase level of RBCs

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What if the sample is already collected and the number of RBCs is
increased but noticed late? (Hct: 57%)
Remedy:

First, calculate the amount of sodium citrate needed
● Recollect specimen

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x-axis

% Hematocrit

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y-axis

mL of sodium citrate remaining in the tube
volume of the sodium citrate to be adjusted

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preserves Factors V and VIll better

SODIUM CITRATE

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If the Factors V and VIlI cannot be
preserved in the sample

Leads to prolonged
coagulation time

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Why is EDTA not used?

● Only for hematological procedures
● inhibits fibrinogen-thrombin reaction

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Factor____ is unstable in its presence

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Frothing (or bubbles) of sample

Shortened coagulation time

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Short draw

PT and PTT are falsely prolonged coagulation time

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Specimen clot : Partially clotted

Shortened coagulation time

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Fully clotted

Prolonged coagulation time

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Visible hemolysis

Shortened coagulation time

premature release of thromboplastin-like substances from the hemolyzed cells

Visible hemolysis

Lipemia or icterus

Prolonged coagulation time

Tourniquet application >1 minute

Shortened coagulation time

Specimen storage at 1-6° C Due to activation coagulation factor VIl and platelets

Shortened coagulation time

precipitation of large von Willebrand factor multimers ● destruction of platelet integrity.

Prolonged coagulation time

Specimen storage at >25° C

Prolonged coagulation time/tests

ambient temperature

15-25 c

activates factor VIl, activates platelets, and precipitates large WF multimers

1-6 c

heat deteriorates coagulation factors V and VIll (labile factors)

>25 C

Storage in household freezer

-20c and 2 weeeks

Storage for 6 months

-70c and 6 months or indefinite

If any assay cannot be performed immediately

Centrifuge within 1 hour of collection

To use frozen specimens after storage

Thawed rapidly at 37°C ● Running water or water bath Tested within 1 hour of the time it is removed from the freezer

If thawed frozen samples cannot be tested immediately

Stored at 1°C to 6°C (refrigerated temperature) for up to 2 hours after thawing

What if 2 specimens are requested for a patient who does not undergo heparin therapy (PTT and PT)? Analyze within: ●___ PTT, PT ● ___: PT only ● The sample is centrifuged but the red cell and plasma is not separated

4 hrs and 24 hrs

Platelet Rich Plasma

Light transmittance aggregometry

Platelet Poor Plasma

Clot-based testing (coagulation testing)

200,000 to 300,000/uL

PRP

PRP Centrifugation:

50 x g for 30 minutes (less revolution/minute or centrifugal force)

PPP Centrifugation:

1500 x g for 10-15 minutes or 4400 x g for 3 minutes

Excessive/vigorous mixing of blood ● O

Shortened coagulation time

Incorrect dilution of reagents

shortened

Use of dirty tubes

Shortened coagulation time

Anemic patient

Shortened coagulation time

Examples of manual

Tilt tube and wire lopp

Timer is initiated and stopped by the operator

Manual

Instrument usually contains a device for maintaining constant 37° C temperature

Semiautomated

Analyzer may internally monitor temperature Instrument has a mechanism to initiate a timing device automatically on addition of final reagent and a mechanism for detecting clot formation and stopping the timer

Semiautomated

● Measures a change in conductivity between two metal electrodes immersed in plasma

MECHANICAL or ELECTROMECHANICAL

When a clot forms, the ___ conducts current between the two probes.

fibrin strand

The ___ inside the cuvette will stop moving when the fibrin clot is formed

steel ball

Involves detection of a change in optical density (absorbance) ● Formation of fibrin threads causes light to scatter allowing less light to fall on the detector

PHOTO-OPTICAL (TURBIDOMETRIC)

PHOTO-OPTICAL (TURBIDOMETRIC) Mechanism:

Fibrin thread or clot formation → scatter → detection of light is decreasing → timer stops

Modification of photo-optical detection in which 90-degree or forward-angle light scatter, rather than OD, is measured

NEPHELOMETRIC

Employs a colorless synthetic oligopeptide substrate conjugated to a chromophore - para-nitroaniline (pNA) - 405 nm

CHROMOGENIC

Principle of chromogenic

Hemostatic factor cleaves the chromogenic substrate at the site binding the oligopeptide to the pNA, freeing the pNA.

OD is proportional to the activity of the analyte being measured

Direct chromogenic assay

Change in OD is thus inversely proportional to the concentration or activity of the substance being measured

Indirect chromogenic assay

We use latex agglutination ○ Uses latex particles coated with antibodies

immunologic

Principle of immunologic

Latex microparticles are coated with antibodies directed against the selected analyte (antigen).

Two of the most used global coagulation assays especially in the hospitals

THROMBOELASTOGRAPHY (TEG) and ROTATIONAL THROMBOELASTOMETRY (ROTEM) and THROMBIN GENERATION ASSAYS (TGA)

Differentiate TEG and ROTEM vs TGA

Used for patients undergoing surgeries or in trauma cases for TEG and ROTEM while Measures general physiologic mechanism for hemostasis for TGA