Mixing Study Interpretation

Inhibitor Screen: Mixing studies use the Rosner Index (RI) to determine if a prolongation corrects. RI > 15 is highly suggestive of a circulating inhibitor or lupus anticoagulant.

APTT Results (Seconds)

Patient APTT

Normal Pool (NPP)

1:1 Mix APTT

Enter Values to Interpret

Guidelines & Evidence

Verified

Last Review: 2026-07-17

When to Use

Investigating an isolated prolongation of the PT or APTT.

Differentiating between factor deficiencies (e.g., Hemophilia) and coagulation inhibitors (e.g., Lupus Anticoagulant, Factor VIII inhibitor).

Screening before specialized factor assays.

The 'Correction' Logic

Since only 50% of the normal factor level is required to achieve a normal PT/APTT, mixing the patient's plasma 1:1 with normal pooled plasma (NPP) should correct a simple deficiency.

How it Works

Pattern Recognition

Pattern	Mixing Study Result	Probable Cause
Correction	APTT normalizes (< 5s above ULN)	Factor Deficiency
No Correction	APTT remains prolonged	Immune Inhibitor
Partial Correction	APTT improves but remains long	Lupus anticoagulant or strong inhibitor

Rosner Index (RI)

RI = [(1:1 Mix APTT - NPP APTT) / Patient APTT] × 100. RI > 15 suggests an inhibitor; RI < 12 suggests deficiency.

Last Comprehensive Review: 2026-07-17

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Clinical Context

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Mixing Study Interpretation

When to Use

When to Use

The 'Correction' Logic

How it Works

Pattern Recognition

Rosner Index (RI)

Clinical Pearls

Time-Dependent Inhibitors

Heparin Interference

The Evidence

Primary Strategy

The laboratory identification of lupus anticoagulants.

Origins & History

Methodology

Recent Journal Updates

Mixing Study Interpretation

When to Use

When to Use

The 'Correction' Logic

How it Works

Pattern Recognition

Rosner Index (RI)

Clinical Pearls

Time-Dependent Inhibitors

Heparin Interference

The Evidence

Primary Strategy

The laboratory identification of lupus anticoagulants.

Origins & History

Methodology

Recent Journal Updates