What is the interpretation of a DRVVT (dilute Russell viper venom test) screen of 49.5 seconds, a PTT (partial thromboplastin time) lupus anticoagulant mix of 48.0 seconds, antiphosphatidylserine IgG 9 U and antiphosphatidylserine IgM 59 U?

Interpretation of Laboratory Results

These results are consistent with lupus anticoagulant (LA) positivity, requiring confirmatory testing with mixing studies and confirm steps to definitively establish LA presence, followed by repeat testing in 12 weeks to confirm persistence before making clinical decisions about antiphospholipid syndrome (APS).

Understanding Your Results

Lupus Anticoagulant Testing (DRVVT and PTT LA Mix)

Your prolonged DRVVT screen (49.5 seconds) and PTT LA mix (48.0 seconds) both suggest the presence of a lupus anticoagulant. However, complete LA testing requires a three-step methodology: screening (which you have), mixing studies, and confirmatory testing with phospholipid-rich reagents 1, 2.

The ISTH 2025 guidance emphasizes that both dRVVT and APTT-based tests should be performed simultaneously, as omitting either test increases the risk of missing LA in up to 55% of triple-positive APS patients 1. Your results show prolongation in both systems, which is actually more clinically significant than single-test positivity 3.

Critical next steps needed:

• Mixing study: Must be performed to distinguish LA from coagulation factor deficiencies
• Confirmatory test: Adding phospholipid-rich reagent should correct the prolonged times if LA is present
• Screen/confirm ratio: Should be calculated and must be ≥1.2 for LA positivity 4

Antiphosphatidylserine Antibodies

• IgG: 9.0 U - This is below the moderate threshold (40 U) established by the 2023 ACR/EULAR criteria 1
• IgM: 59 U - This exceeds the moderate threshold (40 U) but is below the high threshold (80 U) 1

Important context: Antiphosphatidylserine antibodies are not part of the standard diagnostic criteria for APS 1. The cornerstone laboratory tests remain:

1. Lupus anticoagulant (LA)
2. Anticardiolipin antibodies (aCL) - IgG and IgM
3. Anti-β2-glycoprotein I antibodies (aβ2GPI) - IgG and IgM

The 2025 ISTH guidance states that aPS/PT antibodies should not replace LA testing and are not recommended as first-line diagnostic tests 1. They may be useful only when LA testing is unreliable or uncertain 1.

Clinical Interpretation Algorithm

Step 1: Complete the LA Workup

You need the full three-step LA testing completed:

• If mixing study shows non-correction AND confirmatory test shows correction with phospholipid → LA positive
• If either step fails these criteria → LA negative or indeterminate

Step 2: Obtain Standard APS Antibody Panel

You are missing the critical tests:

• Anticardiolipin IgG and IgM (by ELISA)
• Anti-β2-glycoprotein I IgG and IgM (by ELISA)

These are mandatory for proper APS evaluation 1.

Step 3: Risk Stratification Based on Antibody Profile

If LA is confirmed positive:

• Triple positive (LA + aCL + aβ2GPI): Highest thrombotic risk 1
• Double positive (LA + either aCL or aβ2GPI with concordant isotype): Intermediate-high risk 1
• Single LA positive: Lower risk than triple positivity but still clinically significant 1

Regarding your elevated aPS IgM (59 U):

• IgM isotypes are generally considered less clinically relevant than IgG 1
• Single IgM positivity without other antibodies has limited clinical significance 1
• This does NOT substitute for standard aCL or aβ2GPI testing

Step 4: Confirm Persistence

Repeat all positive tests in 12 weeks minimum 1. Transient antibody positivity is insufficient for APS diagnosis. The same antibodies must remain positive on repeat testing 1.

Critical Pitfalls to Avoid

Anticoagulation Interference

Were you on anticoagulation when tested? 1, 2

• Warfarin/VKA: Can cause false-positive LA results due to factor deficiency; mixing studies are essential to avoid this 2, 5
• DOACs: Cause significant interference; testing should ideally be done off anticoagulation or with DOAC removal agents 1
• Heparin: Can interfere; testing during trough periods is preferred 1

Inflammation

Do you have active infection or inflammation? Elevated C-reactive protein can prolong DRVVT times and cause false-positive results 6. If CRP is elevated, interpret LA results with extreme caution and consider retesting when inflammation resolves.

Incomplete Testing

The most common error is making clinical decisions based on incomplete LA workups. Never interpret a prolonged screening test alone as "LA positive" - this leads to misdiagnosis 7, 2.

What This Means Clinically

Current status: Presumptive LA positivity with moderate-titer aPS IgM, but incomplete workup prevents definitive APS diagnosis.

If you have had thrombosis or pregnancy complications:

• Complete the full antibody panel immediately
• Ensure proper LA confirmation with mixing and confirm steps
• Retest in 12 weeks to establish persistence
• Clinical correlation is essential - laboratory results must be interpreted with your clinical history 1

If you have no clinical manifestations:

• You may be an asymptomatic aPL carrier
• Complete testing is still warranted for risk stratification
• Persistence on repeat testing determines long-term management

The presence of both prolonged dRVVT and PTT-based tests (if confirmed) suggests higher thrombotic risk than single-test positivity 3, making complete evaluation even more critical.