|Values are valid only on day of printing.|
Confirming or excluding presence of lupus anticoagulant (LAC) distinguishing LAC from specific coagulation factor inhibitors and nonspecific inhibitors
Investigation of a prolonged activated thromboplastin time, especially when combined with other coagulation studies
Initial testing includes: prothrombin time (PT), activated partial thromboplastin time (APTT), and dilute Russell's viper venom time (DRVVT).
If the PT, APTT, and DRVVT are normal, a computer-generated interpretive comment indicating no evidence of a lupus anticoagulant will be provided.
If PT is > or =14 seconds, PT mix will be performed.
If APTT is >36 seconds, APTT mix will be performed.
If APTT mix is >36 seconds with no evidence of heparin in sample, platelet neutralization procedure (PNP) will be performed.
If DRVVT ratio is > or =1.2, DRVVT mix and DRVVT confirmation will be performed.
If PT, APTT, or DRVVT are prolonged, thrombin time (TT) will be performed.
If TT is >23 seconds, reptilase will be performed.
If appropriate, coagulation factor assays, fibrinogen, D-dimer, Staclot LA, and soluble fibrin monomer will be performed to clarify a significant abnormality in the screening clotting times.
If factor VIII result is <55%, the factor VIII inhibitor screen may be performed along with the Bethesda titering assay, if indicated.
If any test results are abnormal, all results will be reviewed by a coagulation consultant and a Special Coagulation Consultant Interpretation will be provided.
See Lupus Anticoagulant Profile Testing Algorithm in Special Instructions.
Lupus anticoagulant (LAC) is an antibody to negatively charged phospholipid that interferes with phospholipid-dependent coagulation tests.
LAC is found in, but not limited to, patients with systemic lupus erythematosus; LAC is associated with other autoimmune disorders and collagen vascular disease, and occurs in response to medications or certain infections (eg, respiratory tract infections in children) and in individuals with no obvious underlying disease.
LAC has been associated with arterial and venous thrombosis and fetal loss. Individuals with thrombocytopenia or factor II deficiency associated with LAC may be at risk for bleeding.
PROTHROMBIN TIME (PT)
The INR is used only for patients on stable oral anticoagulant therapy. It makes no significant contribution to the diagnosis or treatment of patients whose PT is prolonged for other reasons.
ACTIVATED PARTIAL THROMBOPLASTIN TIME (APTT)
Adults: 26-36 seconds
The normal full-term newborn APTT may be up to 35% longer than in adults and even longer (up to twice the adult upper limit) in healthy premature infants. Typically, the APTT is in the adult reference range by age 3 months in healthy full-term infants and by age 6 months in healthy premature infants (30-60 weeks gestation)*.
26-36 seconds (>3-6 months)
*See Pediatric Hemostasis References in Coagulation Studies in Special Instructions.
DILUTE RUSSELL'S VIPER VENOM TIME
This test is not useful for the detection of antiphospholipid antibodies that do not affect coagulation tests. We recommend separate testing for serum phospholipid (cardiolipin) antibodies.
Patient should not be receiving warfarin or heparin. If the patient is currently on warfarin or heparin, this should be noted, treatment with heparin causes false-positive results of in vitro coagulation testing for lupus anticoagulant. Coumadin treatment may impair ability to detect the more subtle varieties of lupus-like anticoagulants.
1. Arnout J, Vermylen J: Current status and implications of autoimmune antiphospholipid antibodies in relation to thrombotic disease. J of Thromb Haemost 2003 May;1(5):931-942
2. Levin JS, Branch DW, Rauch J: The antiphospholipid syndrome. New Engl J Med 2002 March 7;346(10):752-763
3. Proven A, Bartlett RP, Moder KG et al: Clinical importance of positive tests for lupus anticoagulant and anticardiolipin antibodies. Mayo Clin Proc 2004,79(4):467-475