Assay reflexed to Lupus Inhibitor Evaluation if indicated.

Routine: 2 Hours
Urgent: 1 Hour

Mixing studies received before 1:30 pm are processed the same day; after 1:30 pm, samples are processed the next day. Reflexed lupus testing is batched 2 times per week. Call 503-494-7383 if STAT.

3 LIGHT BLUE top tubes, 3.2% sodium citrate or four (4) 1 mL frozen sodium citrate plasma aliquots. Tubes must be full (see comments below).

3 pediatric 1.3 mL LIGHT BLUE top tube, 3.2% sodium citrate or one 1 mL aliquot of sodium citrate plasma. For pediatric patients requiring multiple coagulation tests, please call 503-494-7383 regarding draw volumes.

Normal Pool, 0 min: 26.0 to 37.9 seconds.
Normal Pool, 60 min: 26.0 to 37.9 seconds.
Lupus studies, see lupus anticoagulant testing.

Draw volume is critical due to the liquid anticoagulant. Allow tubes to fill by vacuum.

• Tubes with rubber stopper: fill to line on label.
• Tubes with plastic (Hemogard) cap: the fill level is above the top of the label.
• Syringe: do not remove the vacutainer stopper. Insert the needle through the stopper and allow the tube to fill by vacuum. Do not overfill the vacutainer.
• Pediatric tubes have no vacuum. Remove the cap and add blood to the 1.3 mL mark. Do not overfill.

Samples for mixing studies (Core lab) and lupus testing (Hemostasis & Thrombosis Lab) sodium citrate specimens must be processed and frozen within 2 hours of specimen collection. OHSU clinics must cab the specimen to the Core Lab, Hatfield Research Center, 9th Floor (room 9D20) if processing is delayed or not possible on site . A phone call is helpful to alert the lab at 503-494-7383. Detailed instructions are under Hemostasis & Thrombosis section (Opens in a new window).

Avoid warfarin (Coumadin) therapy for 2 weeks and heparin/DOAC/DTI therapy for 2 days prior to the test.

Patients with prolonged PTT will be reflexed for a heparin test. Mixes suggestive of an inhibitor will be reflexed for a lupus inhibitor evaluation.

The assay is used to distinguish between circulating inhibitor and coagulation factor deficiency when APTT is prolonged. Test is a screening test for the lupus anti-coagulant. Typically, a patient is identified with a prolonged APTT without a history of bleeding, or perhaps with a history of thrombosis or miscarriage. Failure to correct a prolonged APTT with 1:1 mix suggests a circulating inhibitor. A positive mixing study should be followed by studies to determine whether the inhibitor is a true antibody (i.e. anti-Factor VIII) or an anti-phospholipid antibody (lupus anticoagulant).

Methodology: Clot-based on prolongation of APTT assay.

Mixing studies performed on only mildly elevated partial thromboplastin times are often uninformative due to dilutional effects, therefore mixing studies will not be reflexively performed until the PTT is greater than 2 seconds longer than the upper limit of normal (i.e. greater than 38.9).

1:1 Mix
50 M
50:50 Mix
PTT Mix