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General Information:

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Mayo Clinic Laboratories

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