Lupus anticoagulant testing is used to help determine the cause of an unexplained thrombosis, recurrent fetal loss, or a prolonged PTT test. It is ordered to help determine whether a prolonged PTT is due to a specific inhibitor (an antibody against a specific coagulation factor) or to a nonspecific inhibitor like the lupus anticoagulant. It may be ordered along with anticardiolipin antibody and the anti-beta2-glycoprotein I assay to check for antiphospholipid syndrome. If someone tests positive for the lupus anticoagulant, the test may be done again in several weeks to see if the antibody was transient. Occasionally lupus anticoagulant testing may be ordered to help determine the cause of a positive VDRL/RPR test for syphilis (both anticardiolipin antibodies and lupus anticoagulant may produce a false positive result with these tests).

Because there are other inhibitors and analytical variables that can cause abnormal test results, several different tests are used to confirm the presence of a lupus anticoagulant. Typically these may include: PTT, prothrombin time (PT), dilute or modified Russell viper venom screen (dRVVT or MRVVT), and a hexagonal (II) phase phospholipid assay (Staclot-LA test) or kaolin clotting time. A thrombin time test may also be done to rule out heparin contamination (a drug used for anticoagulant therapy), and a fibrinogen test may be done to rule out abnormal deficiency in fibrinogen. These two conditions can cause prolongations in the test results and interfere with lupus anticoagulant detection.

Lupus anticoagulant testing is ordered when a patient has had an unexplained thrombotic episode, has had recurrent miscarriages, and/or as a follow-up to a prolonged PTT test. If a lupus anticoagulant panel is positive, the person's doctor may want to repeat one or more of the tests several weeks later to determine whether the lupus inhibitor is transitory or chronic.

The doctor may also want to test for the lupus anticoagulant when a patient has a positive anticardiolipin antibody, to evaluate whether ther person has antiphospholipid syndrome.

If someone is negative for the lupus anticoagulant but has an autoimmune disease, such as SLE or a mixed connective tissue disorder, the affected patient's doctor may occasionally order one or more of the lupus anticoagulant screening tests, usually the PTT, to determine whether the antibody has developed since the last time the test was performed. This is done because the person has the potential to develop the lupus anticoagulant at any time.

The results of each of the lupus anticoagulant tests either lead towards or away from the likelihood of having a lupus anticoagulant. Although the tests done may vary, they usually begin with a prolonged PTT.

• If the PTT or LA-PTT is prolonged, and mixing it with normal pooled plasma does not “correct” the result, then it is likely that there is an inhibitor present. If the prolonged test corrects when phospholipid is added, then it is likely that a lupus anticoagulant is present. (After heparin contamination, a lupus anticoagulant is the most common reason for a prolonged PTT).
• If the PTT is not prolonged, there may not be a lupus anticoagulant present, the test reagents may contain too much phospholipid, or the test may not be sensitive enough to pick up the lupus anticoagulant. The LA sensitive PTT may need to be done.
• If a dRVVT or MRVVT test is prolonged and does not correct when mixed with normal pooled plasma but does correct with the addition of phospholipids, then it is likely that a phospholipid antibody is present.
• If a Thrombin Time test is normal, then heparin contamination is excluded.
• If a fibrinogen test is normal, then it is likely that there is sufficient fibrinogen for normal clot formation.

Other tests that may be done to help confirm the diagnosis of a lupus anticoagulant include:

• Platelet Neutralization (this uses platelets as a source of phospholipids)
• Hexagonal (II) Phase Phospholipid Assay (Staclot-LA test)
• Kaolin Clotting Time
• Tissue thromboplastin inhibition test
• VDRL or RPR – these are tests for syphilis. Their reagents are made of cardiolipin and they may give a false positive result for both anticardiolipin antibodies and for lupus anticoagulant.
• Coagulation factors - these may be ordered to rule out factor deficiencies that may cause a prolonged PTT and bleeding episodes
• Prothrombin Time (PT)

Other tests that may be run in addition to lupus anticoagulant testing:

• Anticardiolipin and anti-beta2-glycoprotein I antibodies to check for antiphospholipid syndrome
• Platelet count: Mild to moderate thrombocytopenia is often seen along with the lupus anticoagulant and may be caused by anticoagulant (heparin) therapy.

Patients on heparin or heparin substitute (such as hirudin, danaparoid, or argatroban) anticoagulation therapy may have false positive results for lupus anticoagulant, but those on warfarin (coumadin) anticoagulant therapy should not. If possible, lupus anticoagulant testing should be done prior to the start of anticoagulation therapy. If a patient with a thrombosis has a lupus anticoagulant, it may be necessary to prolong and possibly increase the intensity of their anticoagulation therapy.

In addition to testing for lupus anticoagulant, it may sometimes be necessary to test for coagulation factor VIII levels. Coagulation factor VIII inhibitors (specific antibodies against factor VIII) can decrease factor VIII levels and cause false positive lupus anticoagulant tests. Elevated factor VIII levels, as may be seen in an acute infection or with replacement therapy when someone has Hemophilia A, may shorten the PTT time, leading to a temporary false negative test for lupus anticoagulant.