Collection of samples for lupus anticoagulant (LA) testing should be drawn into 3.2% sodium citrated tubes. Detailed protocols for collection of coagulation samples is outlined in the Clinical and Laboratory Standards' (CLSI) documents Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays (H21) and Laboratory Testing for the Lupus Anticoagulant (H60). This tube should be drawn prior to any tube containing an activating agent (eg, thrombin) which may cause clotting, as well as prior to any tube containing anticoagulants, such as EDTA or heparin, which may prolong results. Tubes should be mixed by gentle inversion to ensure blood and sodium citrate are well mixed. Failure to do so may result in the formation of a clot.
Ratio of blood to anticoagulant
It is important to adhere to the blood to anticoagulant ratio of 9:1. Short draws will be prolonged due to excess anticoagulant and can result in a false positive LA. Patients that present with a hematocrit >55 can also have a prolonged clotting time. The anticoagulant volume should be adjusted for these samples.
These samples should be transported to the laboratory at room temperature. Samples for lupus testing should be processed within four hours of collection. If that is not possible, they should be properly aliquoted and frozen (-20 to -80°C) until they are tested.