Calibration Curve Method

Heparin concentration in the test sample can be directly

obtained from the Liquicelin-E calibration curve by

interpolating the test plasma clotting time against the

heparin concentration in U/mL.

Expected Values

Normal values using Liquicelin-E reagent are between

21 and 29 seconds at 3 minutes activation time. Between

manual and turbodensitometric instrument results a

variation of 1-2 seconds may be expected. For photo-optical

instruments, it is recommended that each laboratory must

establish their own normal range.

Remarks

1. Due to inter and intralaboratory variations users must

establish their own normal population range as well

as normal and abnormal range.

2. It is recommended that controls with known factor

activity should be run simultaneously with each test

series routinely.

3. Incorrect mixture of blood and trisodium citrate,

insufficient prewarming of plasma and reagent,

contaminated reagents, glassware, etc. are potential

source of errors.

4. Incorrect dilutions of heparin is also a potential source

of error.

5. Oxalated plasma may induce prolonged clotting times.

6. Clotting time of patients on anticoagulant therapy

depends upon the type and dosage of anticoagulant

and also the time lag between the specimen collected

and the last dose.

7. Abnormalities of coagulation factor VII, factor XIII and

platelets are not detected by this test procedure.

8. For automated equipment, it is strongly recommended

that the equipments manufacturer’s methodology is

strictly adhered to.

9. In heparin monitoring time of collection of blood

sample is important since the in vivo half-life of

heparin is approximately 1.5 hours. When it is

administered intravenously, it has an immediate

anticoagulant effect but its efficacy decreases rapidly

with time.

10. Platelet factor IV, a heparin-neutralizing factor can

be released due to platelet aggregation or damage.

In order to prevent this phenomenon in vitro the

specimen should be collected with a minimum of

trauma.

11. Decrease in APTT time is observed in males under

estrogen therapy and oral contraceptive administration

in females.

Clinical Implications of APTT

1. The APTT is prolonged in all coagulation defects of

stage I (includes platelet activity and thromboplastin).

2. The APTT is usually prolonged in Willebrand’s disease

and is accompanied by a consistently diminished

factor VIII level.

3. The APTT and PT will detect 95% of coagulation

abnormalities. When APTT is performed in conjunction

with a prothrombin time (PT), a further clarification of

296 Concise Book of Medical Laboratory Technology: Methods and Interpretations coagulation defects is possible. For example, a normal

PT and abnormal APTT means that the defect lies in

the first stage of the clotting mechanism.

Causes of prolonged APTT

¾ Hemophilia

¾ Vitamin K deficiency

¾ Liver disease

¾ Presence of circulating anticoagulants

¾ DIC disease (chronic or acute).

Shortened APTT occurs in:

¾ Extensive cancer, except when liver is involved

¾ Immediately after acute hemorrhage

¾ Very early stages of DIC.

Circulating Anticoagulants

Usually occurs as an inhibitor of a specific factor (e.g. factor

VIII). Most commonly seen in the development of antifactor VIII or anti-factor IX in 5 to 10% of hemophiliacs.

Anticoagulants that develop in the treated hemophiliac

are detected by prolonged APTT. Circulating anticoagulants also can be detected in some cases:

¾ Following repeated plasma transfusions

¾ Drug reactions

¾ Tuberculosis

¾ Chronic glomerulonephritis

¾ Systemic lupus erythematosus

¾ Rheumatoid arthritis.

NORMAL AND ABNORMAL CONTROL PLASMAS

FOR COAGULATION ASSAYS PLASMATROL H-I/II®

(Courtesy: Tulip Group of Companies)

Summary

Tulip Plasmatrol H-l and Plasmatrol H-ll are two level

human plasma controls that are suitable for use as normal

and abnormal control plasma for PT, APTT, TT and

fibrinogen testing using clot based methods. Coagulation

controls provide a means of day-to-day quality control

in the hemostasis laboratory for control of accuracy and

precision.

Reagent

Plasmatrol is a stabilized and freeze dried preparation

of selected human plasma with values determined and

assigned for specific clot based tests, which are lot specific.

The plasma controls are assayed using Tulip coagulation

reagents.

Reagent Storage and Stability

Unopened vials should be stored at 2–8°C and are stable

up to the expiry date mentioned on the vial labels. After

reconstitution the shelf life of the control plasma is 3 hours

at 25–30°C and 8 hours when stored at 2–8°C.

Principle

The properties of the control plasma are similar to those

of pooled fresh plasmas. Since, the plasma controls have

assigned values, when substituted in place of a sample, in

clot based coagulation assays, they can be used for laboratory quality assurance.

Note