Lupus anticoagulant testing with optical end point automation.
The dilute Russell viper venom time and kaolin clotting time (KCT) are very sensitive screening tests for lupus anticoagulant activity. However, due to the high turbidity of the kaolin reagent it is difficult to accommodate the KCT on the optical end point automation of today. We evaluated five recently reported screening tests (the silica clotting time, the Textarin/Ecarin ratio, the Taipan venom time, the factor V ratio, and a kaolin clotting time using low-turbidity kaolin) as potential alternatives to the KCT. The sensitivity and specificity of the silica clotting time compared well to KCT, detecting 10/12 KCT positive samples and showing equal sensitivity to dilution of lupus positive plasma. In addition, the silica clotting time allows for a confirmatory phospholipid correction procedure. False-positive results were seen in 2 of 15 warfarinised samples. A second assay utilising the ratio of extrinsic/intrinsic factor V assays was not affected by either warfarin or heparin. This assay also gave positive results with 3 of 23 samples previously screened as lupus negative but exhibiting anticardiolipin positivity. It was therefore concluded that a combination of the silica clotting time and dilute Russell viper venom time met the requirements of lupus sensitivity with demonstration of phospholipid dependence and optical end point compatibility. The factor V ratio is a useful second-line screen for both anticoagulated patients and anticardiolipin antibody-positive samples.
Luddington
R
R
Department of Haematology, Addenbrookes NHS Trust, Cambridge, United Kingdom. rluddington@yahoo.com
Scales
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C
Baglin
T
T
D000925:Anticoagulants / Q000494:pharmacology; D016736:Antiphospholipid Syndrome / Q000097:blood; D001327:Autoimmune Diseases / Q000097:blood; D001331:Automation; D001780:Blood Coagulation Tests; D004546:Elapid Venoms; D010450:Endopeptidases; D005069:Evaluation Studies as Topic; D005165:Factor V / Q000032:analysis; D005189:False Positive Reactions; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007616:Kaolin / Q000737:chemistry; D008107:Liver Diseases / Q000097:blood; D016682:Lupus Coagulation Inhibitor / Q000097:blood*; D008180:Lupus Erythematosus, Systemic / Q000097:blood; D009391:Nephelometry and Turbidimetry; D010314:Partial Thromboplastin Time; D010447:Peptide Hydrolases; D011184:Postoperative Period; D011516:Prothrombin; D011517:Prothrombin Time; D012822:Silicon Dioxide; D014859:Warfarin / Q000494:pharmacology
D000925:Anticoagulants; D004546:Elapid Venoms; D016682:Lupus Coagulation Inhibitor; C023558:prothrombin activator (Taipan venom); D007616:Kaolin; D014859:Warfarin; D012822:Silicon Dioxide; C037525:textilotoxin; D005165:Factor V; D011516:Prothrombin; D006493:Heparin; D010450:Endopeptidases; D010447:Peptide Hydrolases; C020097:ecarin