What should be done for an adult patient with elevated lactate levels, potentially indicating metabolic or respiratory issues?

Elevated LA/DRVVT Ratio: Lupus Anticoagulant Evaluation

A LA/DRVVT ratio of 2.34 is highly suggestive of lupus anticoagulant (LA) positivity and requires confirmatory testing with a mixing study followed by phospholipid neutralization to establish the diagnosis.

Understanding the Test Result

• The dilute Russell viper venom time (DRVVT) is a phospholipid-dependent coagulation test used to screen for lupus anticoagulants 1
• A LA/DRVVT ratio >1.2 typically indicates a prolonged clotting time suggestive of a phospholipid-dependent inhibitor 1
• Your ratio of 2.34 represents significant prolongation, strongly suggesting the presence of lupus anticoagulant 1

Immediate Next Steps

Perform confirmatory testing within 12 weeks:

• Mixing study: Mix patient plasma 1:1 with normal pooled plasma - if the prolonged clotting time does NOT correct (remains prolonged), this confirms an inhibitor rather than a factor deficiency 1
• Phospholipid neutralization/confirmation: Add excess phospholipid to the test - if the prolonged time corrects (normalizes), this confirms the inhibitor is phospholipid-dependent (i.e., lupus anticoagulant) 1
• Repeat testing in 12 weeks: LA must be positive on two separate occasions at least 12 weeks apart to meet diagnostic criteria for antiphospholipid syndrome 1

Clinical Assessment Required

Evaluate for thrombotic events and pregnancy complications:

• Assess for history of arterial thrombosis (stroke, MI, peripheral arterial occlusion) 1
• Assess for history of venous thromboembolism (DVT, PE, unusual site thrombosis like hepatic/portal/mesenteric veins) 1
• In women of childbearing age, inquire about recurrent pregnancy loss (≥3 unexplained consecutive miscarriages <10 weeks gestation, or ≥1 unexplained fetal death ≥10 weeks) 1
• Evaluate for obstetric complications including severe preeclampsia, placental insufficiency, or HELLP syndrome 1

Additional Laboratory Testing

Complete the antiphospholipid antibody panel:

• Anti-cardiolipin antibodies (IgG and IgM) - medium to high titer (>40 GPL or MPL units, or >99th percentile) 1
• Anti-β2-glycoprotein I antibodies (IgG and IgM) - medium to high titer (>99th percentile) 1
• These must also be positive on two occasions at least 12 weeks apart for APS diagnosis 1

Critical Pitfalls to Avoid

• Do not start anticoagulation based on LA positivity alone - the presence of LA does not automatically indicate need for anticoagulation unless there is a history of thrombosis or other APS criteria are met 1
• Do not diagnose antiphospholipid syndrome with a single positive test - requires persistent positivity over 12 weeks 1
• Do not confuse LA with bleeding risk - despite prolonging clotting times in vitro, lupus anticoagulant is associated with thrombosis, not bleeding 1
• Avoid testing during acute illness or anticoagulation - heparin interferes with DRVVT testing; warfarin affects interpretation; direct oral anticoagulants can cause false positives 1

Management Algorithm Based on Clinical Context

If patient has prior thrombosis + confirmed LA:

• Lifelong anticoagulation is indicated (warfarin target INR 2-3, or DOAC in selected cases) 1
• Consider higher intensity anticoagulation (INR 3-4) for recurrent thrombosis despite therapeutic anticoagulation 1

If patient has no prior thrombosis but confirmed LA:

• No anticoagulation required for primary prevention in most cases 1
• Consider low-dose aspirin in high-risk patients (multiple positive antibodies, cardiovascular risk factors) 1
• Provide thromboprophylaxis during high-risk periods (surgery, immobilization, pregnancy) 1

If pregnant patient with confirmed LA and obstetric APS:

• Low-dose aspirin (75-100 mg daily) plus prophylactic low molecular weight heparin throughout pregnancy 1
• Continue anticoagulation for 6 weeks postpartum 1