What does this LOINC code represent?

This LOINC code identifies a lab observation, measurement, question, or clinical concept in a standardized format.

Is this enough to understand my test result?

No. The code identifies the test or observation, but the interpretation depends on the actual result, reference range, and clinical context.

LOINCActiveBoth

LOINC Code 81643-9: vWf ristocetin cofactor act/vWf Ag (PPP) [Ratio]

Name: LOINC Code 81643-9: vWf ristocetin cofactor act/vWf Ag (PPP) [Ratio]
Creator: HealthAssure Clinical Team
Published: 2026-05-21T09:00:05.775Z

81643-9 is a LOINC code used to identify vWf ristocetin cofactor act/vWf Ag (PPP) [Ratio] in laboratory and clinical observation data. You may see this code in lab systems, lab reports, EHR exports, interoperability feeds, or other structured clinical data exchanges. LOINC codes identify tests, measurements, observations, survey items, and clinical questions in a standardized way. It is associated with the component von Willebrand factor.ristocetin cofactor activity/von Willebrand factor Ag. It is commonly used with the system or sample type PPP.

Reviewed by HealthAssure Clinical TeamUpdated 21 May 2026

What is this code?

LOINC codes identify tests, measurements, observations, survey items, and clinical questions in a standardized way. It is associated with the component von Willebrand factor.ristocetin cofactor activity/von Willebrand factor Ag. It is commonly used with the system or sample type PPP.

When is it used?

Used in lab systems, EHRs, and clinical data exchange.
May identify a test, observation, survey item, or clinical document request rather than a diagnosis.
Status: ACTIVE
Order vs observation: Both

What it does not mean

The code identifies the observation or test, not the actual result.

Key facts

von Willebrand factor (vWf) ristocetin cofactor/von Willebrand factor (vWf) Ag [Ratio] in Platelet poor plasma

von Willebrand factor.ristocetin cofactor activity/von Willebrand factor Ag

This term represents a ratio of two results that are expressed as percentages of normalthe von Willebrand factor.ristocetin cofactor activity and the von Willebrand factor antigen concentration, both of which are reported as actual/Normal. The von Willebrand factor (vWF) ristocetin cofactor activity to antigen ratio can help distinguish different types of von Willebrand disease (VWD). VWD types 1 and 3 are usually associated with a quantitative decrease in vWF, which would affect both the vWF ristocetin cofactor activity as well as vWF antigen concentration, while type 2 is associated with a functional defect in VWF, which would affect the activity but not the amount of antigen present. Therefore, patients with type 2 VWD are likely to have a lower vWF ristocetin cofactor activity to antigen ratio (less than 0.6-0.7) compared to patients with types 1 or 3 VWD.

Activ; Actvty; AggRecetin; COAGULATION; Cofact; Fac; Fact; Hematology; Heme; Movements; Plas; Platelet poor plasma; Point in time; QNT; Quan; Quant; Quantitative; Random; Ratios; Risto; Rto; Von will; Von willebrand factor activity; Vonwillebrand; vWf; vWf Activity; vWFAg; vWf:RCo

Where you may see this code

You may see this code in lab systems, lab reports, EHR exports, interoperability feeds, or other structured clinical data exchanges.

Common synonyms

vWf ristocetin cofactor act/vWf Ag (PPP) [Ratio]von Willebrand factor (vWf) ristocetin cofactor/von Willebrand factor (vWf) Ag [Ratio] in Platelet poor plasmavWf:RCo/vWF Ag PPP-Rtovon Willebrand factor.ristocetin cofactor activity/von Willebrand factor AgCOAGvWf Ristocetin Cofactor Activity/Antigen, BloodRatio

Frequently asked questions

Code details

Code81643-9

SystemLOINC

Display namevWf ristocetin cofactor act/vWf Ag (PPP) [Ratio]

Descriptionvon Willebrand factor.ristocetin cofactor activity/von Willebrand factor Ag

Short namevWf:RCo/vWF Ag PPP-Rto

Componentvon Willebrand factor.ristocetin cofactor activity/von Willebrand factor Ag

PropertyRatio

TimingPt

System (specimen)PPP

ScaleQn

ClassCOAG

Example unitsratio

StatusACTIVE

Order/ObservationBoth

Flags

BillableNo

Valid clinical useNo

Source

SourceLOINC

Version2.82

Releasemain

First released2.56

Last changed2.73

Consumer names

vWf Ristocetin Cofactor Activity/Antigen, Blood

Part names

von Willebrand factor.ristocetin cofactor activity/von Willebrand factor AgRatioPtPPPQnPoint in time (spot)Platelet poor plasma

About this content

This page is prepared by HealthAssure's clinical team using official coding standards from LOINC. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.