Ratio of factor V activities in PT and APTT assays as a new diagnostic marker of lupus anticoagulant

Abstract

Lupus anticoagulant (LA) is an antibody that interferes with phospholipid-dependent coagulation tests. We investigated the usefulness of the ratio of factor V activity determined by the Simplastin auto test (PT assay) to factor V activity determined by the Platelin Excel LS test (APTT assay) for detection of LA in plasma samples obtained from 276 patients with haematological and non-haematological disorders and 73 healthy subjects. This ratio was significantly higher in the 15 LA-positive (4.82 +/- 3.34) than in samples from healthy subjects (1.09 +/- 0.10) and was > 1.4 in 10 of the remaining 261 patient samples. The ratio was particularly low in the 54 samples from warfarin-treated patients. These findings suggest that determination of this ratio may be useful as a routine laboratory test for detection of LA. This test requires no specific antigens and can be applied in patients receiving anticoagulants such as warfarin and heparin.

The Antiphospholipid Syndrome: What are We Really Measuring? How do We Measure it? And How do We Treat it?

“…The TCT should be normal in a patient with an antiphospholipid antibody who is not receiving heparin therapy. In addition, comparison of factor V results obtained by PT-based and aPTT-based assays can help identify the presence of an antiphospholipid antibody [25]. Factor assays may also prove useful in certain situations, to evaluate for a specific factor inhibitor.…”

Testing for Lupus Anticoagulants

“…81 Perhaps this might be the springboard to revisit a previously described but not routinely adopted sensitive and specific LA detection procedure generating a ratio of FV activity values from prothrombin time and aPTT-based factor assays. 82 LA is an in vitro phenomenon, so an elevated screen and mix with a corrected confirm, after exclusion of interferences, is by definition an LA irrespective of the parent assay. An important question is whether assays other than dRVVT and aPTT-based assays detect clinically significant antibodies, which has been demonstrated to be the case for dPT, ASLA, Textarin time, and TSVT.…”

“…81 Perhaps this might be the springboard to revisit a previously described but not routinely adopted sensitive and specific LA detection procedure generating a ratio of FV activity values from prothrombin time and aPTT-based factor assays. 82…”

Prothrombin time inhibition detected with recombinant but not with conventional thromboplastins in two patients with high-titre IgM and moderate-titre IgA anticardiolipin antibodies

“…The standard PT is usually either normal or only slightly prolonged. It has been postulated that differences in the effects of APA on certain coagulation parameters in the presence of different phospholipids depends on the relationship between the nature of the antibody and the specificity of phospholipid factors (Amagai et al. 1999).…”

“…The standard PT is usually either normal or only slightly prolonged. It has been postulated that differences in the effects of APA on certain coagulation parameters in the presence of different phospholipids depends on the relationship between the nature of the antibody and the speci®city of phospholipid factors (Amagai et al 1999). Although the functional anticoagulant speci®city of IgG fractions of APA is well documented (Pengo et al 1987;Bevers et al 1991;Rao et al 1995;Pierangeli et al 1997;Zhu et al 1999), that of IgM and IgA proteins, with a few notable exceptions (Hasegawa et al 1994;Thiagarajan et al 1980) is less well described.…”