What are the limitations of the lac reporting framework?

While the lac reporting framework is highly validated, it should not replace clinical judgment. OpiCalc provides the latest evidence-based limitations for the lac reporting framework to ensure safe bedside use and optimal diagnostic accuracy.

How does the lac reporting framework compare to other hematology scores?

The lac reporting framework is a gold-standard diagnostic tool. OpiCalc provides side-by-side clinical guidance to help clinicians choose the most specific evidence-based tool for their patient's presentation.

Is the lac reporting framework free to use?

Yes. OpiCalc provides the lac reporting framework completely ad-free and optimized for mobile bedside use, ensuring you can calculate medical risk swiftly and without distraction.

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Lupus Anticoagulant (LAC) Reporting Framework

LAC Interface: Standardized reporting for dRVVT or SCT. Follows the ISTH algorithm: Screen-Mix-Confirm.

Test Metrics (seconds)

Screening Time

Mixing Time (1:1 with Normal)

Normal Pooled Plasma (NPP)

Confirmatory Step

High Phospholipid Time

Sustained correction by phospholipids confirms LAC.

Guidelines & Evidence

Clinical Details

Section 1

When to Use

Interpreting screening tests for Lupus Anticoagulant (LAC).

Applying the ISTH three-step algorithm (Screen → Mix → Confirm).

Differentiating LAC-mediated prolongation from coagulation factor deficiencies.

Patient Population

Patients with clinical suspicion of Antiphospholipid Syndrome (APS), unexplained prolongation of the aPTT, or recurrent pregnancy loss.

When Not to Rely on This Score Alone

Anticoagulant Therapy — Warfarin, DOACs, and Heparins can cause false-positive LAC results. Ideally, test when the patient is off anticoagulation (or use specialized procedures like Taipan Snake Venom Time).

Acute Phase — LAC testing should not be performed during an acute thrombotic event or inflammatory state.

Diagnosis of APS — requires persistence of the LAC for ≥ 12 weeks.

Section 2

Formula & Logic

Step 1: Screen (Prolongation)

A phospholipid-dependent screening test (e.g., dRVVT or Silica Clotting Time) is prolonged beyond the reference range.

Step 2: Mix (Correction failure)

Patient plasma is mixed 1:1 with normal pooled plasma. If the clotting time does NOT correct (Index of Circulating Anticoagulant > 12–15%), an inhibitor is present.

Step 3: Confirm (Correction by PL)

High-concentration phospholipids are added. If the clotting time shortens significantly (Confirmatory Ratio > 1.2), the inhibitor is phospholipid-dependent (LAC).

Section 3

Pearls/Pitfalls

The dRVVT vs. aPTT

The dilute Russell Viper Venom Time (dRVVT) is more specific for LAC than the aPTT, as it activates Factor X directly, bypassing the contact phase (Factors XII, XI, IX, VIII).

Index of Circulating Anticoagulant (ICA)

ICA = [(Mix - Normal) / Patient] × 100. Values > 15 are strongly suggestive of an inhibitor.

Section 4

Evidence Appraisal

Guidelines

Update of the guidelines for lupus anticoagulant detection. Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies of the Scientific and Standardization Committee of the ISTH.

Pengo V et al. • Journal of Thrombosis and Haemostasis. 2009;7(10):1737-40.

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Section 5

Literature

Definition

"Lupus Anticoagulant" is a misnomer: it is found in many non-SLE patients and it is pro-thrombotic in vivo, despite prolonging clotting times in vitro.

Last Comprehensive Review: 2026

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