Most important is to work with platelet-poor plasma (PPP) when testing for LA. PPP is defined as plasma that contains <10 x 109/L platelets. Samples should be centrifuged using at least 1,500 g forces (3,000 rpm) for at least 15 minutes. A swing-out bucket should be used and the break should not be applied. If PPP cannot be obtained, then samples should be double centrifuged. After the initial spin, plasma should be carefully removed and placed into a polypropylene tube and respun. Centrifuges should be checked at least annually to demonstrate PPP is properly produced.
Platelets are a source of phospholipids. If platelets are present in plasma, they can overwhelm or neutralize a LA, leading to shortened results. Even worse is when a sample containing platelets is frozen and thawed. Platelets will then burst and release excess phospholipids, resulting in a false negative result. Therefore, when aliquoting plasma, it is crucial NOT to pick up cells from the buffy coat, which will contain platelets and contaminate the plasma, resulting in platelets neutralizing the LA.
