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HelpTest Code LAB478 Lupus Inhibitor Screen (Intrinsic Pathway)
Useful For
A screening test for the detection of a lupus anticoagulant. Prolongation of the activated partial thromboplastin time (APTT) can occur as a result of deficiency of one or more coagulation factors (acquired or congenital in origin), or the presence of an inhibitor of coagulation such as heparin, a lupus anticoagulant, a nonspecific inhibitor such as a monoclonal immunoglobulin, or a specific coagulation factor inhibitor.
Methodology
Clot Detection
Profile Information
| Test Code | Test Name |
Available Separately |
Always Performed |
|---|---|---|---|
| LAB325 | Partial Thromboplastin Time Activated (APTT) | Yes | Yes |
Testing Algorithm:
If the APTT is prolonged > 3SD of the normal range, an APTT Mixing study will be performed at an additional charge. A thrombin time will be performed to rule out the presence of heparin.
Reflex Tests
| Test Code | Test Name | Test Components |
|---|---|---|
| N/A | APTT Mixing Study | PTT Patient Plasma/Normal Plasma Mix 1:1 Mix |
| PTT Patient Plasma/Factor Diluent Mix 1:1 | ||
| Thrombin Time | ||
| Pathologist Interpretation |
Performing Laboratory
Bozeman Health Laboratory Services
Specimen Requirements
Specimen must arrive and be tested within 4 hours of draw.
Specimen Type: Whole blood
Container/Tube: Blue top (3.2% sodium citrate)
Specimen Volume: Full tube
Collection Instructions: Click here to link to a You Tube video tutorial
1. Immediately after draw, invert tubes several times to mix blood with additive.
2. Send specimen in original tube.
3. If there is a delay in transport of >4 hours, specimen must be double-centrifuged to prepare a platelet-free plasma specimen as follows:
a. Immediately centrifuge at 3,200 rpm for 15 minutes.
b. Carefully remove plasma from cells avoiding platelet/buffy coat, and transfer plasma into a plastic tube.
c. Centrifuge plastic tube at 3,200 rpm for 15 minutes.
d. Carefully remove top portion of plasma and transfer plasma into a plastic tube leaving approximately 250 mcL in bottom to discard.
e. Double-centrifuged plasma should be aliquoted (0.5 mL-1 mL each) into clearly labeled plastic tubes. (Glass vial is not acceptable.)
Note: Number of tests ordered will determine number of aliquots needed, generally 1 aliquot per test.
f. Specimens should be frozen at <-40° C, if possible, and sent together in same container with at least 5 lbs of dry ice. Specimens must arrive in a frozen state.
4. If the patient has a hematocrit of >55 (within the last 14 days):
a. A new 'Adjust Tube' will automatically be ordered.
b. Phlebotomist or RN should contact the lab to obtain a tube with the correct anticoagulant ratio.
c. The lab will mark the tube appropriately as 'adjusted'.
d. Tube will be sent by the lab to the phlebotomist or RN to draw the patient.
e. Process the 'adjusted' tube as stated above in steps 1-3.
Additional Information: Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.
Specimen Transport Temperature
Ambient (whole blood) <4 hours/Frozen (plasma) >4 hours
Specimen Stability
| Specimen Type | Temperature | Time |
|---|---|---|
| Whole Blood (unspun) | Ambient | 4 hours |
| Plasma Na Citrate (spun) | Ambient | 4 hours |
| Plasma Na Citrate (double spun) | Frozen | 14 days |
Reference Values
24.4-35.4 seconds
3SD reflex value: ≥ 38.2
Critical value (automatic call-back): >100 seconds
Day(s) Test Set Up
Monday through Sunday
Test Classification and CPT Coding
85730
85730 PTT
85732 PTT plasma fraction (if needed)
85670 Thrombin Time (if needed)
80500-Pathology Interp