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Test Code PTT Partial Thromboplastin Time (PTT), Plasma

Important Note

Useful for:

Monitoring heparin therapy (unfractionated heparin)

Screening for certain coagulation factor deficiencies

Detection of coagulation inhibitors such as lupus anticoagulant, specific factor inhibitors and non specific inhibitors

Performing Laboratory

MaineGeneral Medical Center

Specimen Requirements

Citrated Plasma

Do not draw specimen from an arm with a heparin lock or heparinized catheter.

Heparinized patient samples must be spun within 1 hour of draw and tested within 2 hours of draw.

Collect blood in a blue-top 0.109M (3.2%) buffered sodium citrate tube. Invert several times to mix. Label the specimen with the patient's name (first and last), date of birth, date and time of draw and the collector's initials. Send sodium citrate whole blood in the original VACUTAINER®. Foward unprocessed whole blood promptly to the lab.

Heparinized patient samples must be spun within 1 hour of draw and tested within 2 hours of draw.

Routine samples can be left on the cells for up to 4 hours at room temperature. If unable to perform testing within 4 hours, centrifuge specimen for 10 minutes at 3,000 rpm, remove plasma and place 0.5 mL of citrate plasma in plastic vial. (Glass vial is not acceptable.) Send the plasma frozen in a plastic vial.

Specimen Stability

Specimens for routine aPTT assays on non-heparinized patients, uncentrifuged or centrifuged with plasma remainng on top of the cells in an unopened tube kept at room temperature (18-24°C), should be tested within four hours of collection.

 

Specimens containing unfractionated heparin should be centrifuged within one hour of collection, kept refrigerated at 18-24°C , and the plasma tested within 2-4 hours from time of collection.

 

If testing is not completed within 4 hours, the plasma should be frozen in a capped plastic tube at ≤-20°C for up to two weeks.

Minimum Volume

The proportion of blood to anticoagulant volume must be 9:1.

Specimen tube must be filled to at least 90% of capacity of the collection tube. Fill to the line indicated on the tube.

Specimen Rejection Criteria

Under or over filled tubes

Wrong anticoagulant used

Hemolysis

Clotted sample

Blood contaminated with heparin

Samples exceeding stated storage limits

Reference Values

Normal range:     23.8 - 31.7 seconds

Therapeutic range:  85 - 117 seconds

Critical value (automatic call-back):  ≥120.0 seconds

Day(s) Test Performed

Monday - Sunday

Test Classification and CPT Coding

85730