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Test Code LAB0207282 aPTT Mixing Studies (Activated Partial Thromboplastin Time), Plasma

Methodology

 

Photometric Clot Detection

Screening for certain coagulation factor deficiencies and abnormalities (eg, factor VIII, IX, XI, or XII)

 

A thrombin time is run on patient's sample before proceeding with the mixing study to rule out heparin contamination  in the sample.

Performing Laboratory

CentraCare Laboratory Services

Specimen Requirements

Specimen Type: Plasma

Container/Tube: Light-blue top (3.2% sodium citrate) tube, properly filled. Prefer 2.7 or 5 ml tubes

Specimen Volume:3 mL

Collection Instructions:

1. Draw a full tube. This tube must be second tube drawn.

2. Centrifuge for 10 minutes at 3,000 rpm.

3. Remove an aliquot of plasma into a plastic tube with plastic pipette.

4. Centrifuge aliquot of plasma for 10 minutes then carefully remove plasma into a second aliquot tube being careful not to pick up any platelets or RBCs.

5. If there is a delay in testing of >4 hours, freeze plasma immediately at -20° C and send frozen in plastic vial.

Specimen Transport Temperature

Refrigerated 4 hours/Frozen OK

Reference Values

25.1-36.5 seconds
Critical value (automatic call-back): >65 seconds

Note: This critical value changes each year with new lot numbers of reagents.

 

Correction of the APTT mix to within the normal reference range usually indicates a coagulation factor deficiency.  If the prolonged APTT is due to an inhibitor (eg, specific coagulation factor inhibitor, lupus anticoagulant, heparin), the APTT mix typically fails to correct a prolonged APTT.

Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding

85730  APTT

85670 Thrombin Time