Summary
Lupus anticoagulants belong to the family of antiphospholipid antibodies. They include
two phospholipid-dependent inhibitors of coagulation that may be distinguished on
the basis of specific coagulation profiles generated from the comparison of the ratios
of the Kaolin Clotting Time (KCT) and the dilute Russell’s Viper Venom Time (dRVVT):
when the ratio of the KCT exceeds that of the dRVVT, the plasma is allocated to the
“KCT” coagulation profile, when the opposite occurs, the plasma is defined to belong
to the “dRVVT” coagulation profile group. We prospectively followed-up a historical
cohort of 100 consecutive patients with lupus anticoagulants referred to our Institution
between January 1988 and October 1997 to investigate the relationship between their
coagulation profile at diagnosis and the development of thrombosis during a median
follow-up time of 37.5 months (range 1-115 months). Fifty-six patients were allocated
to the “dRVVT” coagulation profile, whereas the other 44 displayed the “KCT” profile.
Lupus anticoagulants were transient in 17 patients, without differences between the
two groups. None of these patients developed clinical events before disappearance
of the phospholipid-dependent inhibitors of coagulation. The 83 cases with persistent
lupus anticoagulants consistently displayed the same coagulation profile they had
been allocated to at entry. Fourteen patients developed 18 thromboembolic events during
the follow-up, with an overall rate of thrombosis of 4.2% patients-year. Twelve of
them belonged to the “dRVVT” coagulation profile, whereas the other 2 to the “KCT”
profile (p = 0.03). The “dRVVT” coagulation profile gave an odds ratio of thrombosis
of 5.25 (95% confidence interval [C.I.]: 1.17-23.50). Ten of the 14 patients who developed
thrombosis during follow-up had already experienced thrombosis: a previous thrombotic
event caused an odds ratio of recurrency of 2.72 (95% C.I.: 0.85-8.73) (p = 0.09).
By multivariate analysis, the “dRVVT” coagulation profile was still associated with
a trend to a higher risk of thrombosis, but the difference did not reach statistical
significance. Increased levels of anticardiolipin antibodies (> 40 GPL and/or MPL
units) were found in all the 14 patients (p = 0.0064). The “KCT” coagulation profile
was significantly associated (p = 0.005) with moderate thrombocytopenia (platelets
50-150 × 109/l). Neither profile was found to represent a risk factor for the development of recurrent
miscarriages, neoplastic diseases and death. In conclusion, the “dRVVT” profile appears
to have predictive value with respect to the thrombotic complications suffered by
patients with antiphospholipid antibodies.