What are the limitations of the mixing study interpretation?

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

How does the mixing study interpretation compare to other Hematology scores?

The mixing study interpretation 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 mixing study interpretation free to use?

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

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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

Clinical Details

Section 1

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.

Section 2

Formula & Logic

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.

Section 3

Pearls/Pitfalls

Time-Dependent Inhibitors

Factor VIII inhibitors are often temperature and time-dependent. A mix that "corrects" initially but prolongs after 2 hours of incubation at 37°C is highly suggestive of an acquired FVIII inhibitor.

Heparin Interference

Mixing studies cannot differentiate between an inhibitor and residual Heparin in the sample. Always perform a Thrombin Time (TT) or Heparinase-neutralized check if contamination is suspected.

Section 4

Evidence Appraisal

Primary Strategy

The laboratory identification of lupus anticoagulants.

Kershaw G et al. • Seminars in Thrombosis and Hemostasis. 2012;38(4):375-84.

View Source

Section 5

Literature

Methodology

Normal Pooled Plasma (NPP) must be platelet-poor (< 10 × 10⁹/L) to prevent neutralization of lupus anticoagulants by platelet phospholipids.

Last Comprehensive Review: 2026

Guidelines & Evidence

Clinical Details

Section 1

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.

Section 2

Formula & Logic

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.

Section 3

Pearls/Pitfalls

Time-Dependent Inhibitors

Factor VIII inhibitors are often temperature and time-dependent. A mix that "corrects" initially but prolongs after 2 hours of incubation at 37°C is highly suggestive of an acquired FVIII inhibitor.

Heparin Interference

Mixing studies cannot differentiate between an inhibitor and residual Heparin in the sample. Always perform a Thrombin Time (TT) or Heparinase-neutralized check if contamination is suspected.

Section 4

Evidence Appraisal

Primary Strategy

The laboratory identification of lupus anticoagulants.

Kershaw G et al. • Seminars in Thrombosis and Hemostasis. 2012;38(4):375-84.

View Source

Section 5

Literature

Methodology

Normal Pooled Plasma (NPP) must be platelet-poor (< 10 × 10⁹/L) to prevent neutralization of lupus anticoagulants by platelet phospholipids.

Last Comprehensive Review: 2026

Related Hematology Tools

PLASMIC Score

French TTP Score

PNH Clone Size Interpreter

LDH/AST Ratio

ISTH Bleeding Assessment Tool

PBT

von Willebrand Factor Activity Interpreter

Haemophilia Severity Classification

Factor Inhibitor Bethesda Titre Interpreter

ISTH Non-Overt DIC Score

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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

Clinical Details

Section 1

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.

Section 2

Formula & Logic

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.

Section 3

Pearls/Pitfalls

Time-Dependent Inhibitors

Factor VIII inhibitors are often temperature and time-dependent. A mix that "corrects" initially but prolongs after 2 hours of incubation at 37°C is highly suggestive of an acquired FVIII inhibitor.

Heparin Interference

Mixing studies cannot differentiate between an inhibitor and residual Heparin in the sample. Always perform a Thrombin Time (TT) or Heparinase-neutralized check if contamination is suspected.

Section 4

Evidence Appraisal

Primary Strategy

The laboratory identification of lupus anticoagulants.

Kershaw G et al. • Seminars in Thrombosis and Hemostasis. 2012;38(4):375-84.

View Source

Section 5

Literature

Methodology

Normal Pooled Plasma (NPP) must be platelet-poor (< 10 × 10⁹/L) to prevent neutralization of lupus anticoagulants by platelet phospholipids.

Last Comprehensive Review: 2026

Guidelines & Evidence

Clinical Details

Section 1

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.

Section 2

Formula & Logic

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.

Section 3

Pearls/Pitfalls

Time-Dependent Inhibitors

Factor VIII inhibitors are often temperature and time-dependent. A mix that "corrects" initially but prolongs after 2 hours of incubation at 37°C is highly suggestive of an acquired FVIII inhibitor.

Heparin Interference

Mixing studies cannot differentiate between an inhibitor and residual Heparin in the sample. Always perform a Thrombin Time (TT) or Heparinase-neutralized check if contamination is suspected.

Section 4