Platform
Company
Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
The TTP-LA Preliminary test is a version of the partial thromboplastin time designed to be sensitive to lupus anticoagulant, an antibody that can interfere with phospholipid-dependent clotting reactions. It measures how long your plasma takes to form a clot under specific laboratory conditions that reduce available phospholipid.
This test is used as a screening step when your care team is looking for antiphospholipid antibodies, especially lupus anticoagulant, or when a routine clotting test is unexpectedly prolonged. By itself it does not diagnose a condition; results are interpreted together with confirmatory assays and your medical history.
Finding evidence of a lupus anticoagulant can help explain unexplained blood clots or certain pregnancy complications, and it may change how your clinician manages your care. A preliminary screen that reacts to lupus anticoagulant helps decide whether more specific testing is needed and whether any test interference from medications should be considered.
This test is commonly ordered if you have an abnormal routine clotting test, a history of clotting events, repeated pregnancy loss, or an autoimmune condition. It may also be used before procedures to understand clotting behavior and to plan safe use of blood thinners.
A result within the laboratory’s expected range suggests that a strong lupus anticoagulant is less likely at the time of testing, though it does not completely rule it out. A prolonged result can point to lupus anticoagulant, but similar patterns can occur with clotting factor deficiencies, other inhibitors, or the effects of blood thinners.
If your result is abnormal, your care team may add a mixing study and phospholipid neutralization or dilute Russell viper venom testing to clarify the cause. If you are taking heparin or a direct oral anticoagulant, your clinician may adjust timing or repeat testing when it is safe, because these medicines can distort results. Persistently abnormal findings on repeat testing, considered with your symptoms and history, guide next steps and treatment.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Heparin, direct oral anticoagulants, and sometimes warfarin can prolong clotting times or cause false positives. Do not stop any medicine without medical advice; your clinician will decide on timing or alternatives for accurate testing.
Underfilled citrate tubes, clotted samples, hemolysis, or delayed processing can alter clotting results. Proper tube fill, prompt centrifugation, and correct storage are important to avoid spurious prolongation.
Recent infections, surgery, or inflammation can transiently affect clotting tests and lupus anticoagulant activity. Your clinician may recommend repeat testing after recovery to confirm whether an abnormality persists.
Physiologic changes in pregnancy can influence clotting results, and antiphospholipid antibodies may be associated with pregnancy complications. Interpretation should consider gestational status and clinical history.
Markedly elevated hematocrit or the presence of abnormal proteins in blood can affect citrate anticoagulant ratios and assay behavior, potentially skewing results unless the collection and assay are adjusted.
Testing performed soon after a dose of a blood thinner is more likely to be affected. When safe, your care team may choose a time point with minimal drug effect or use drug-neutralizing methods where available.
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