TRIPASS XR تري باس

 

each laboratory must calibrate the necessary force and

time required during centrifugation to yield PPP.

2. Incorrect mixture of blood and Profact is a potential

source of error both in coagulation assays and ESR

estimation.

3. If the reagent vial develops turbidity, do not use the

reagent as this would lead to erroneous results.

Calibration of Instruments/Equipments

¾ Water baths or heating blocks calibrated and preset

at 37 + 0.5°C are an important requirement to achieve

accuracy and reproducibility.

• The whole process of the coagulation tests is based on

a series of enzymatic reactions, which are dependent

on pH, ionic strength and the temperature of the

reaction process. A correct temperature at 37 +

0.5°C is critical as most of the reagent systems

are standardized at this temperature. Day-to-day

shift in reaction temperature of equipment will

introduce uncontrolled variation into test conditions. Therefore, temperature of all equipments must

be calibrated daily and diligently to avoid erroneous

results and ensure accuracy and reproducibility.

• Sample/reagent dispensing mechanisms must be

accurate and precise.

• Well-calibrated dispensing mechanisms are required

for all coagulation- based tests to accurately dispense

samples as well as reagents. Any shift in ratio or

individual volumes of the sample and/or reagent can

lead to shortening or prolongation of results.

• Straight 0.1 and 0.2 mL glass pipettes are usually

satisfactory, provided they are scrupulously clean

and dry.

• Automatic micropipettes, which are able to deliver

the required volumes, are replacing the glass pipettes,

provided these pipettes are calibrated frequently.

The use of clean disposable tips places this system

at an advantage over the older mechanisms.

Storage of Reagents

¾ Usually reagent manufacturers recommend aspiration

of adequate reagent for the days use in a thoroughly

clean and dry tube instead of intermittent aspiration

from reagent vials at the time of test.

• Most coagulation reagents are extremely delicate

reagents. For them to maintain their sensitivity and

performance the reagent formulations must maintain

reagent integrity over the usage period. Repeated

intrusions into the reagent vial exponentially

increases the chances of reagent contamination

and destruction of reagent formulations and

integrity. Undried and/or contaminated pipettes,

tips, glassware are usually the main culprits. Such

contaminated reagents perform suboptimally.

• The reagent vials must be immediately stored back

to the recommended storage temperatures after

the aspiration of the day's requirement separately

so that the remaining reagent remains at optimal

temperature for future use. Keeping unused reagents

at higher ambient temperatures during the day

causes steady deterioration of the reagent due to

thermal stress.

¾ The recommended storage temperature for reagents

should be strictly complied to:

• Most of the liquid stable or reconstituted reagents

such as PT and APTT are colloidal suspensions of

lipoproteins and/or phospholipids. Subjecting them

to elevated temperatures through repeated freezethaw cycles stresses the colloidal system. Especially

detrimental are the effects of freezing (below 2°C).

After freezing the reagent colloidal suspension

undergoes an irreversible change and precipitates

out or present itself as a particulate mass. Such

reagents give erroneous results.

¾ Bringing reagents/samples to room temperature

should be a two-step process:

• When enough reagents are aspirated out for the

days testing as recommended the reagent and

samples stored at 2 to 8°C should be first allowed to

attain room temperature (25 to 30°C) and then they

should be subsequently brought to the optimal test

temperature of 37 + 0.5°C.

• When reagent samples from 2 to 8°C are directly

brought to 37°C the required time of 3 to 5 minutes

may not be sufficient for the reagent samples to

attain a homogeneous temperature of 37°C within

the recommended time. This affects the reaction

kinetics leading to erroneous results.

282 Concise Book of Medical Laboratory Technology: Methods and Interpretations End Point Reading

¾ Reading of endpoint of clot-based tests varies from user

to user.

• Usually when manual techniques are followed the

definition of “end point” is important. Ideally, the

end point tests should be read “as soon as the first

fibrin strand is visible and the gel clot formation

begins”

• When some users use a fully formed gel clot as an

end point, there is a variation of 1 to 3 seconds

between the end points as recorded by the ideal

method and user-based variation.

• It is advisable to have well illuminated background

for reading the clot-based end points. Since user

variations based on proficiency continue to influence

results, it is advisable not to change personnel

involved in coagulation tests off and on.

¾ Manufacturer’s instructions must be followed meticulously when instrument based or automatic clot

detection systems are used.

• Each clot detection system works on a different

p r i n c i p l e , s u c h a s e l e c t r o m e c h a n i c a l ,

turbidimetric or photo-optical. Each system of

clot detection has its requirements for optimum

functioning. Special care must be taken while

using optical instruments for clot detection since

reagent-induced turbidity can influence the

results dramatically. Usually low turbidity reagents

are preferred for manual as well as instrumentsbased clot detection.

Drug/Clinical Conditions Influencing Patient Results

¾ Drugs/clinical conditions influence results of patients

coagulation studies.

PT tests are influenced on administration of following

drugs

PT may be shortened PT may be prolonged

drugs drugs

• Antihistamines • Corticosteroids

• Butabarbital • EDTA

• Phenobarbital • Asparaginase

• Caffeine • Clofibrate

• Oral contraceptives • Erythromycin

• Vitamin K • Ethanol

• Tetracycline

• Aspirin

• Anticoagulants such as

warfarin and heparin

APTT tests are influenced on administration of

following drugs

APTT may be shortened APTT may be prolonged

drugs drugs

• Oral contraceptives • Diphenylhydantoin

• Conjugated estrogen • Heparin

therapy • Warfarin

• Naloxone

• Radiographic agents

Thrombin time test is prolonged in the following clinical

conditions

• Normal newborn infant • Hepatic diseases

• Systemic lupus • Toxemia of

erythematosus pregnancy

• Macroglobulinemia • Multiple myeloma

• Presence of exogenous/

endogenous circulating

anticoagulants

Mean Normal Prothrombin (MNPT) and International

Normalized Ratio (INR)

¾ MNPT is a critical requirement in the derivation of INR.

¾ MNPT is a critical requirement in the derivation of

INR. Ideally each laboratory must derive its own MNPT

from 20 or more normal patients for a given PT reagent

and Lot under use. This corrects within laboratory test

variables that influence PT results.

¾ By definition INR represents the PT ratio which would

have been obtained for a particular patient sample as if

the WHO reference thromboplastin itself (ISI=1.0) had

been used in the PT determination.

INR = [R][ISI]

INR = Patient PT in seconds

Mean of the normal range

ISI

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