Tripodi et al described the Lupus Anticoagulant Sensitivity Index (LASI). This is similar to the International Normalized Index (INR) for the prothrombin time (PT). The authors are from IRCCS Ca Granda Ospedlae Maggiore Policlinico Foundation, Universita degli Studi di Milano and University Hospital Padova in Italy.


Patient selection: presence of lupus anticoagulant (LA)


The LASI (Lupus Anticoagulant Sensitivity Index) is derived by comparing different methods for detection of lupus anticoagulants using a common standard material. It is calculated from the slope of each method plotted with dilutions of the standard versus the logarithm of the clotting time (CT).


The lower the LASI value the more responsive the test is in detecting a lupus anticoagulant. LASI values may range from 0.1 to 4.5 with the silica clotting time (SCT) assigned a value of 1.



(1) patient result for clotting time (CT) in seconds

(2) clotting time for normal control in seconds

(3) LASI value for the clotting time testing system


LA ratio =

= (patient result) / (normal control result)


standardized LA ratio = SLA ratio =

= (LA ratio) ^ (LASI)


The standardized LA ratio minimizes the variability between different methods for detecting lupus anticoagulant


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