Test Details
Methodology
The VWF:CB assay tests the capacity of plasma VWF to bind collagen. Human Type III collagen is used. After plasma sample incubation with the collagen, residual unbound proteins are removed by washing procedures. The bound VWF is detected with anti-VWF antibodies and an assay-specific detection system.
Result Turnaround Time
5 - 9 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Test Includes
This test includes vWF collagen-binding activity (VWF:CB); vWF antigen (VWF:Ag); and VWF:CB/VWF:Ag ratio.
Use
This test is used to screen for the presence of type II von Willebrand disease in plasma.
Limitations
This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.
Low VWF:CB levels will be present in individuals with quantitative defects (i.e., type 1 and type 3 VWD), as well as most individuals with qualitative defects (i.e., types 2A and 2B VWD). Since this assay will not differentially identify individuals with different types of VWD on its own and may also be normal in some forms of vWD (i.e., type 2 N VWD), it is important that other VWF assays including VWF:Ag and VWF:Ac (i.e., GPIb binding) assays also be employed when assessing individuals for suspected VWD. For a more comprehensive review of VWD and the tests used for diagnosing this condition, refer to Test No. 086282.
The use of VWF:CB assays has been demonstrated to be less sensitive than GPIb binding (VWF:Ac) assays, with some individuals with type 2A VWD being classified as having type 1 VWD if the only functional assay performed was VWF:CB.1,2
The VWF:CB/VWF:Ag ratio may be used as an adjunct to multimer analysis,3,4 but it must be noted that the use of VWF:CB/VWF:Ag ratios is less sensitive than multimer analysis in some individuals with VWD.5
A low value for just one of VWF:Ac/vWF:Ag or VWF:CB/VWF:Ag is not compatible with relative depletion of HMWM and points to either type 2M VWD or potentially a pre-analytic or analytic error in one of the VWF binding assays. In these cases, repeat testing on a fresh sample for confirmation is recommended.
Custom Additional Information
Von Willebrand Disease (VWD) is the most common congenital bleeding disorder and arises from deficiency and/or defect in plasma von Willebrand Factor (VWF).3,6,7 Three main VWD types are recognized, with six sub-types (1, 2A, 2B, 2M, 2N, 3) identified according to current International Society on Thrombosis and Haemostasis (ISTH) classification.3,6,7
Types 1 and 3 identify quantitative deficiency of VWF, respectively partial or (virtually) total. In Types 1 and 3, any VWF present is functionally normal, albeit deficient in quantity. Type 2 VWD defines qualitative defects of VWF, although VWF levels are also quantitatively low in many patients. Type 2A VWD identifies patients with a specific loss of high molecular weight multimers of VWF (HMWM), the VWF form that has greatest specific adhesive activity. Type 2A VWD patients suffer from loss of VWF activity binding to both platelets (primarily via glycoprotein lb; GPlb) and subendothelial matrix components (predominantly collagen). Type 2B VWD identifies patients with hyper-functional VWF, which spontaneously binds platelets, thereby causing clearance of (predominantly HMWM) VWF and platelets from circulation, and often a (mild) thrombocytopenia. Type 2N VWD reflects a loss of VWF-FVIII binding; thus, increasing FVIII susceptibility to degradation, and reducing plasma FVIII levels. Type 2M VWD reflects a heterogeneous group with defective VWF not associated with loss of HMWM.
In addition to clinical assessment of patients, VWD diagnosis is supported by laboratory testing.3,6,7,8 A standard test recommended by most guidelines involves measurement of VWF antigen (VWF:Ag), VWF GP1b binding activity (VWF:Ac) and factor VIII activity (FVIII). VWF:Ag testing is important due to complexity and heterogeneity of VWD and permits quantifying absolute levels of (total) VWF protein. VWF:Ac measurement assesses the extent to which the VWF in the sample can bind GP1b, reflecting diminished HMWM and/or genetic defect compromising this function. FVIII testing is important since one major function of VWF is to bind and protect FVIII from degradation. Thus, FVIII is often low in VWD, a condition that contributes to any bleeding diathesis (especially types 3, 2N and severe type 1 VWD). Additional assays may be used to support the diagnosis of VWD. VWF collagen binding activity (VWF:CB) is also recommended in guidelines.3,9 In vivo, collagen binding permits anchorage of platelets to damaged endothelium, enabling VWF to act as an adhesive bridge to capture platelets. Assessment of VWF multimers is also useful, particularly to help identify loss of HMWM (types 2A or 2B VWD), and potentially discriminate these from types without such loss (type 1 or 2M VWD). For a more comprehensive review of VWD and the tests used for diagnosing this condition, refer to Test No. 086282.
The assessment of the ability VWF to bind to collagen can support the diagnosis and subtyping of VWD.3,9-15 Fully functional VWF binds both platelet glycoprotein 1b (GPIb) and collagen via separate binding sites. VWF:CB reflects a different, but still major, VWF activity relative to VWF:Ac. VWF:CB and VWF:Ac assay results can both be diminished in cases of concomitant genetic defects in the separate binding sites for collagen and GP1b. More commonly, patients with diminished functional VWF (i.e., diminished HMWM) will have a reduction in both VWF:CB and VWF:Ac assay results reflecting an overall functional protein deficit. Patients with type 2A or 2B VWD are reported to have a more severe bleeding phenotype than the subset of patients with 2M VWD with a loss of GPIb binding but normal collagen binding.15-22
One can calculate a ratio of VWF:CB to VWF:Ag to determine the relative VWF:CB activity of the VWF present in the patient’s plasma.12,14 The VWF:CB/VWF:Ag ratio will be normal when the VWF in the patient’s plasma is fully functional with regard to collagen binding activity but will be reduced in individuals with a compromising genetic defect in the collagen binding locus of the VWF molecules and/or a relative reduction of HMWM as a fraction of total VWF. The VWF:CB/VWF:Ag ratio will be greater than 0.7 in healthy individuals (with normal levels of functional protein) and in individuals with types 1 (with low levels of functional protein) and 2N VWD (with normal collagen binding function and impaired Factor VIII binding function). VWF:CB and VWF:Ag ratios would be expected to be concordant (>0.7) in type 3 VWD, but imprecision of the tests at the very low levels seen in these patients limits the accuracy and thus utility of the ratio.
If both VWF:Ac/VWF:Ag and VWF:CB/VWF:Ag are low, the most likely scenarios are type 2A or 2B. Most cases of type 2M VWD are caused by VWF mutations that lead to loss of GPIb binding (identified by VWF:Ac/VWF:Ag). These mutations typically have limited or no effect on collagen binding and thus VWF:CB/VWF:Ag ratios are usually normal, or at least closer to normal than VWF:Ac/VWF:Ag.17 However, a minority type 2M cases have deficits in both ratios. A diminished VWF:CB/VWF:Ag in concert with diminished VWF:Ac/VWF:Ag can also be seen many cases of acquired VWD and in the very rare platelet type VWD.10
A rare subset of individuals with type 2M VWD with reduced VWF:CB but normal VWF:Ac can be misdiagnosed if only a VWF:Ac assay is performed during the initial investigation for VWD.23 However, recent guidance suggests these defects are extremely rare such that VWF:CB assays do not need to be performed as part of the initial investigation for VWD diagnosis.24
Specimen Requirements
Specimen
Plasma, frozen
Volume
2.0 mL
Minimum Volume
1.0 mL (Note: This volume will not allow for repeat testing.)
Container
Blue-top (sodium citrate) tube
Collection Instructions
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.25 Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio.26,27 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. With a winged blood collection set, a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacuated tube.28,29 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternative anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
Reference Range
CBA activity: 50% to 150%
CBA ratio: 0.6−5.0
vWF antigen: 50% to 150%
Storage Instructions
Freeze; four freeze/thaw cycles are acceptable. Stable refrigerated for four hours.
Causes for Rejection
Lipemia; icteric specimen; hemolysis; clotted specimen; specimen contaminated with heparin (i.e., drawn with blood gases)
Footnotes
1. Boender J, Eikenboom J, van der Bom JG, et al. Clinically relevant differences between assays for von Willebrand factor activity. J Thromb Haemost. 2018 Dec;16(12):2413-2424. PubMed 30358069
2. Flood VH, Gill JC, Friedman KD, et al. Collagen binding provides a sensitive screen for variant von Willebrand disease. Clin Chem. 2013 Apr;59(4):684-961. PubMed 23340442
3. James PD, Connell NT, Ameer B, et al. ASH ISTH NHF WFH 2021 guidelines on the diagnosis of von Willebrand disease. Blood Adv. 2021 Jan 12;5(1):280-300. PubMed 33570651
4. Federici AB. Current and emerging approaches for assessing von Willebrand disease in 2016. Int J Lab Hematol. 2016 May;38 Suppl 1:41-49. PubMed 27426859
5. Perez-Rodriguez A, Batlle J, Corrales I, et al. Role of multimeric analysis of von Willebrand factor (VWF) in von Willebrand disease (VWD) diagnosis: lessons from the PCM-EVW- ES Spanish project. PLoS One. 2018 Jun 20;13(6):e0197876. PubMed 29924855
6. Patton S, Baker P, Bowyer A, et al. Guideline for laboratory diagnosis and monitoring of von Willebrand disease: a joint guideline from the United Kingdom haemophilia Centre Doctors` organization and the British Society for haematology. Br J Haematol. 2024 May;204(5):1714-1731. PubMed 38532595
7. Kaur V, Elghawy O, Deshpande S, Riley D. von Willebrand disease: A guide for the internist. Cleve Clin J Med. 2024 Feb 2;91(2):119-127. PubMed 38307601
8. Patzke J, Binder NB, Bono M, et al. Review of laboratory methods used for analysis of von Willebrand factor and for diagnosis of related diseases. Expert Rev Hematol. 2025 Jul 4:1-15. PubMed 40613465
9. Laffan MA, Lester W, O'Donnell JS, et al. The diagnosis and management of van Willebrand disease: a United Kingdom Haemophilia Centre Doctors Organization guideline approved by the British Committee for Standards in Haematology. Br J Haematol. 2014 Nov;167(4):453-465. PubMed 25113304
10. Favaloro EJ. The Role of the von Willebrand Factor Collagen-Binding Assay (VWF:CB) in the Diagnosis and Treatment of von Willebrand Disease (VWD) and Way Beyond: A Comprehensive 36-Year History. Semin Thromb Hemost. 2024 Feb;50(1):43-80. PubMed 36807283
11. Kimiaei A, Pruner I, Farm M, et al. Ratio of Von Willebrand Collagen Binding Assay and Von Willebrand Antigen Can Predict Multimer Size in Von Willebrand Disease. Haemophilia. 2025 May;31(3):450-457. PubMed 40052420
12. Favaloro EJ. Utility of the von Willebrand factor collagen binding assay in the diagnosis of von Willebrand disease. Am J Hematol. 2017 Jan;92(1):114-118. PubMed 27622788
13. Baronciani L, Federici AB, Cozzi G, Canciani MT, Mannucci PM. von Willebrand factor collagen binding assay in von Willebrand disease type 2A, 2B, and 2M. J Thromb Haemost. 2006 Sep;4(9):2088-2090. PubMed 16961623
14. Keesler DA, Flood VH. Current issues in diagnosis and treatment of von Willebrand disease. Res Pract Thromb Haemost. 2017 Dec 12;2(1):34-41. PubMed 30046704
15. Maas DPMSM, Atiq F, Blijlevens NMA, et al. Von Willebrand disease type 2M: Correlation between genotype and phenotype. J Thromb Haemost. 2022 Feb;20(2):316-327. PubMed 34758185
16. Castaman G, Federici AB, Tosetto A, et al. Different bleeding risk in type 2A and 2M von Willebrand disease: a 2-year prospective study in 107 patients. J Thromb Haemost. 2012 Apr;10(4):632-638. PubMed 22329792
17. Favaloro EJ, Pasalic L, Curnow J. Type 2M and type 2A von Willebrand disease: similar but different. Semin Thromb Hemost. 2016 Jul;42(5):483-497. PubMed 27148841
18. Woods AI, Paiva J, Primrose DM, Blanco AM, Sanchez-Luceros A. Type 2A and 2M von Willebrand disease: differences in phenotypic parameters according to the affected domain by disease-causing variants and assessment of pathophysiological mechanisms. Semin Thromb Hemost. 2021 Oct;47(7):862-874. PubMed 34130347
19. Favaloro EJ, Mohammed S, Vong R, et al. How we diagnose 2M von Willebrand disease (VWD): use of a strategic algorithmic approach to distinguish 2M VWD from other VWD types. Haemophilia. 2021 Jan;27(1):137-148. PubMed 33215808
20. Motum P, Just S, Zebeljan D, et al. A diagnosis of von Willebrand disease despite normal test results for factor VIII and von Willebrand factor antigen and activity. Am J Hematol. 2019 Dec;94(12):1425-1432. PubMed 31423628
21. Castaman G, Federici AB, Tosetto A et al. Different bleeding risk in type 2A and 2M von Willebrand disease: a 2-year prospective study in 107 patients. J Thromb Haemost. 2012 Apr;10(4):632-638. PubMed 22329792
22. Iarossi M, Hermans C. New insights into the diagnosis and management of patients with type 2M von Willebrand disease. Res Pract Thromb Haemost. 2023 Oct 10;7(7):102216. PubMed 38077821
23. Keeling D, Beavis J, Marr R, Sukhu K, Bignell P. A family with type 2M VWD with normal VWF:RCo but reduced VWF:CB and a M1761K mutation in the A3 domain. Haemophilia. 2012 Jan;18(1):e33. PubMed 22004444
24. Platton S, Baker P, Bowyer A, et al. Guideline for laboratory diagnosis and monitoring of von Willebrand disease: a joint guideline from the United Kingdom haemophilia Centre Doctors` organization and the British Society for haematology. Br J Haematol. 2024;204(5):1714-1731. PubMed 38532595
25. Adcock DM, Kressin DC, Marlar RA. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol. 1997 Jan;107(1):105-110. PubMed 8980376
26. Reneke J, Etzell J, Leslie S, Ng VL, Gottfried EL. Prolonged prothrombin time and activated partial thromboplastin time due to underfilled specimen tubes with 109 mmol/L (3.2%) citrate anticoagulant. Am J Clin Pathol. 1998 Jun;109(6):754-757. PubMed 9620035
27. National Committee for Clinical Laboratory Standardization. Collection, Transport, and Processing of Blood Specimens for Coagulation Testing and General Performance of Coagulation Assays; Approved Guideline. 5th ed. Villanova, Pa: NCCLS; 2008. Document H21-A5:28(5).
28. Gottfried EL, Adachi MM. Prothrombin time and activated partial thromboplastin time can be performed on the first tube. Am J Clin Pathol. 1997 Jun;107(6):681-683. PubMed 9169665
29. McGlasson DL, More L, Best HA, Norris WL, Doe RH, Ray H. Drawing specimens for coagulation testing: Is a second tube necessary? Clin Lab Sci. 1999 May-Jun;12(3):137-139. PubMed 10539100
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 117169 | Collagen-Binding Activity | 086280 | vWF Antigen | % | 27816-8 | |
| 117169 | Collagen-Binding Activity | 117177 | Collagen Binding Activity(CBA) | % | 50377-1 | |
| 117169 | Collagen-Binding Activity | 117179 | vWF Collagen/Antigen | Ratio | 50378-9 | |
| Order Code | 117169 | |||||
| Order Code Name | Collagen-Binding Activity | |||||
| Order Loinc | ||||||
| Result Code | 086280 | |||||
| Result Code Name | vWF Antigen | |||||
| UofM | % | |||||
| Result LOINC | 27816-8 | |||||
| Order Code | 117169 | |||||
| Order Code Name | Collagen-Binding Activity | |||||
| Order Loinc | ||||||
| Result Code | 117177 | |||||
| Result Code Name | Collagen Binding Activity(CBA) | |||||
| UofM | % | |||||
| Result LOINC | 50377-1 | |||||
| Order Code | 117169 | |||||
| Order Code Name | Collagen-Binding Activity | |||||
| Order Loinc | ||||||
| Result Code | 117179 | |||||
| Result Code Name | vWF Collagen/Antigen | |||||
| UofM | Ratio | |||||
| Result LOINC | 50378-9 |