What prevents lupus anticoagulant detection in a plasma sample if blood is not centrifuged long enough?

Residual Platelets in Plasma Prevent Lupus Anticoagulant Detection

Increased platelets in the plasma sample will prevent the detection of lupus anticoagulant if blood is not centrifuged for a sufficient time. 1

Why Platelet Contamination Affects LA Testing

The International Society on Thrombosis and Haemostasis (ISTH) guidelines for lupus anticoagulant detection specifically address the critical importance of proper plasma preparation:

1. Double Centrifugation Requirement:

   • Initial centrifugation: 2000g for 15 minutes at room temperature
   • Second centrifugation: >2500g for an additional 10 minutes 1

2. Mechanism of Interference:

   • Residual platelets in plasma samples release phospholipids upon freezing-thawing
   • These phospholipids can neutralize (quench) lupus anticoagulants
   • This neutralization can lead to false-negative results 2

Evidence Supporting Platelet Interference

Research has demonstrated that residual platelets significantly affect LA detection:

• While some LA tests may still detect strong LA positivity in samples with residual platelets, the percentage correction for Silica Clotting Time (SCT) and clotting time difference for Staclot LA are significantly reduced 2
• Median percentage correction decreases from 67% in filtered (platelet-poor) plasma to 54% in non-filtered plasma 2
• This reduction can cause weak LA to be missed completely upon freezing-thawing of non-filtered plasmas 2

Proper Sample Processing Protocol

To ensure accurate LA detection, the ISTH guidelines recommend:

1. Careful Plasma Transfer:

   • After initial centrifugation, transfer plasma to a non-activating plastic tube using a plastic pipette
   • After second centrifugation, carefully aliquot without disturbing the platelet pellet 1

2. Important Caution:

   • "When aliquoting to a secondary tube, take care to not include the residual platelets that may have collected at the bottom of the centrifuge tube" 1

3. Filtration Considerations:

   • Plasma filtration is not recommended by ISTH due to variables introduced (filter type, volume filtered)
   • However, some research supports using 0.2μm filter units to remove residual platelets 3

Other Factors That Do Not Primarily Affect LA Detection

While residual platelets are the primary concern:

• White Blood Cells: Not specifically identified as interfering with LA detection in the guidelines
• Red Blood Cells: Not specifically identified as interfering with LA detection in the guidelines
• Centrifugation Time: Definitely affects LA detection, but only through its impact on residual platelet content 1, 4

Clinical Implications

The accurate detection of lupus anticoagulant is critical because:

• False-negative results may miss patients who need anticoagulant therapy
• False-positive results may lead to unnecessary long-term anticoagulant treatment 1
• LA is a key laboratory criterion for antiphospholipid syndrome diagnosis, which has significant implications for thrombosis risk and pregnancy outcomes 5

Therefore, proper sample preparation with adequate centrifugation to remove platelets is essential for accurate LA testing and appropriate patient management.