What are the limitations of the vwf activity interpreter?

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

How does the vwf activity interpreter compare to other Hematology scores?

The vwf activity interpreter 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 vwf activity interpreter free to use?

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

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von Willebrand Factor Activity Interpreter

VWD Panel Triage: The ratio of Activity (RCo) to Antigen (Ag) is the primary engine for differentiating quantitative (Type 1) from qualitative (Type 2) defects.

Input Panel (Units: %)

VWF Antigen (VWF:Ag)

VWF Activity (VWF:RCo)

Awaiting Lab Values

Guidelines & Evidence

Clinical Details

Section 1

When to Use

Interpreting VWF Antigen (VWF:Ag) and VWF Activity (VWF:RCo) results in patients with suspected VWD.

Differentiating between Quantitative (Type 1) and Qualitative (Type 2) von Willebrand Disease.

Evaluating Factor VIII levels in the context of VWF carrier function.

Timing and Stress

VWF is an acute phase reactant. Levels may be falsely elevated (masking VWD) during pregnancy, infection, or after exercise. Repeat testing is often required.

Section 2

Formula & Logic

VWF:RCo to VWF:Ag Ratio

A ratio of < 0.6 strongly suggests a qualitative defect (Type 2 VWD), as the functioning protein is significantly lower than the total amount of protein present.

VWD Classification Criteria

Type	VWF:Ag	VWF:RCo	Ratio (RCo/Ag)	Description
Type 1	Low (< 30-50%)	Low	> 0.6	Partial quantitative deficiency.
Type 2	Low or Normal	Very Low	< 0.6	Qualitative functional defect.
Type 3	Absent (< 5%)	Absent	N/A	Severe total deficiency.

Section 3

Pearls/Pitfalls

The 'Low VWF' Grey Zone

Recent ASH/ISTH/WFH guidelines define VWD as VWF:RCo < 30%. Levels between 30% and 50% are categorized as "Low VWF," where patients may still have bleeding risks but may not meet the formal genetic criteria for VWD.

Blood Type O Effect

Individuals with Blood Type O naturally have ~25% lower VWF levels than non-O individuals. Reference ranges should strictly consider ABO blood type for accurate diagnosis.

Section 4

Evidence Appraisal

Primary Strategy

ASH ISTH NHF WFH 2021 guidelines on the diagnosis of von Willebrand disease.

James PD et al. • Blood Advances. 2021;Current international gold standard.

View Source

Section 5

Literature

History

Named after Erik von Willebrand, a Finnish physician who first described the disorder in 1926 in a family from the Åland Islands.

Last Comprehensive Review: 2026

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