VWD Diagnostic Tests

Various tests included in the diagnosis of VWD are: bleeding history, total blood count, VWF profile/screening tests (VWF: Ag, VWF: RCo, FVIII: C). If initial test results show VWD, optional tests include: VWF multimer analysis, VWF: CBA, VWF: FVIIIB, RIPA, Genetic testing.2

Bleeding History

It has a supportive role in the diagnosis of VWD.3

Complete Blood Count

This parameter includes evaluation of hemoglobin, hematocrit, platelet count (PC) and morphology, prothrombin time (PT), activated partial thromboplastin time (aPTT). Fibrinogen level or thrombin time (TT) can be measured optionally.4 Generally, individuals with VWD have normal thrombin time, prothrombin time, platelet count, and fibrinogen level. Some individuals have a prolonged aPTT consistent with VWD, while it may be normal in mild or moderate cases. Depending on the type and severity of the disease, hemoglobin and hematocrit levels range from normal to decreasing.5

VWF:Ag (VWF antigen) Test

Tests used to measure VWF plasma concentration. The plasma concentration of VWF is measured using methods such as enzyme-linked immunosorbent assay (ELISA) or automated latex immunoassay (LIA). Results are expressed in international units (IU) as IU/dl or IU/ml.19 Normal VWF range: Ag is 50-200 IU/dl.15 Levels may be reduced in type 1, 2A, 2B individuals while normal or decreased in type 2M . VWF in type 2N VWD: Ag levels are normal. In type 3, it is usually immeasurably reduced.2

VWF: RCo (Ristocetin Cofactor Activity Test)

It is a function assay that measures the ability of VWF to agglutinate with normal platelets. This interaction between VWF and normal platelets is initiated by an antibiotic, ristocetin.19 The normal range is 50-200 IU/dl.1 Levels are decreased in type 1, 2A, 2B VWD and are found at normal levels in type 2N individuals. It may be normal or decreased in type 2M individuals.2

FVIII: C (FVIII Coagulant Activity Test)

It is a functional FVIII assay used to measure the ability of VWF to serve as a carrier protein for FVIII. Its normal range is 50-150 IU/dl. At 15 VWH, its value may decrease or be normal. Always decreases in type 2N and type 3 VWH.2

VWF multimer analysis

This test is not done alone as an initial screening test unless there is sufficient baseline information to recommend VWD. Von Willebrand factor (vWF) multimer analysis is essentially a qualitative test to identify variants of type II von Willebrand disease. Type 2A VWD contains only smaller multimers in plasma, while type 2M contains larger multimers. All multimer sizes can be observed in type 1 VWH plasma. On the other hand, type 3 VWH plasma does not show any multimer distribution.4,6

VWF: CBA (VWF collagen binding test)

This test helps measure VWF binding to collagen. Larger multimers bind better to collagen than smaller ones.7,8 VWF: Together with the VWF: RCo and VWF: Ag tests, VWF: CBA functions to differentiate type 1 from type 2A, 2B, or 2M VWD.9,10

VWF: FVIIIB (VWF: FVIII binding test)

This test detects factor VIII binding defect on VWF.11 In other words, it is used to measure VWF's ability to bind to exogenously added factor VIII. This test is used to diagnose type 2N VWD.12 The amount of factor VIII bound is estimated using the chromogenic FVIII test. In type 2N (homozygous or compound heterozygous), circulating VWF does not normally bind with FVIII and therefore the amount of FVIII is reduced.4

RIPA (Ristocetin-Induced Platelet Aggregation)

RIPA is an ex vivo test used to measure the function of viable platelets. It is mainly used to diagnose type 2B VWD. Usually done using low concentration ristocetin.4

Genetic Tests

Mutation analysis is used to identify mutations in the VWF gene associated with types 2A, 2B, 2M, 2N and some other forms of type 1 and 3 VWD. It is useful in distinguishing mild hemophilia A from type 2N. Mild hemophilia A lacks VWF mutations and follows X-linked inheritance; whereas type 2N is caused by VWF mutations and follows autosomal recessive inheritance. It is also used to distinguish type 2B from type 2M and 2B from 2A.14,15 Mutation analysis also helps manage future pregnancies by identifying the causative mutation in families with type 3 VWD.17 This analysis is a complex and variable less useful in diagnosing type 1 VWD with a genetic basis.14

References
  1. Goodeve AC, James P. Von Willebrand Disease. http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=geneandpart=vonwillebrand
  2. Pruthi RK. A practical approach to genetic testing for von Willebrand Disease. Mayo Clin Proc 2006;81:679-91
  3. Rodeghiero F, Castaman G, Tosetto A. The discriminant power of bleeding history for the diagnosis of type 1 VWD: An international, multicenter study. J Thromb Haemost 2005;3:2619-26.
  4. National Heart, Lung, and Blood Institute, U.S. Department of Health and Human services. The diagnosis, evaluation, and management of von Willebrand disease. Available from: http://www.nhlbi.nih.gov/guidelines/ vwd/3_diagnosisandevaluation.htm
  5. Federici AB. Diagnosis of inherited von Willebrand disease: A clinical perspective. Semin Thromb Haemost 2006;32:555-65.
  6. McPherson RA. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia: Elseiver Saunders; 2011
  7. Favaloro EJ. Detection of von Willebrand disorder and identification of qualitative von Willebrand factor defects: Direct comparision of commercial ELISA-based von Willebrand factor activity options. Am J Clin Pathol 2000;114:608-18
  8. Neugebauer BM, Goy C, Budek I, Seitz R. Comparision of two von Willebrand factor collagen-binding assays with different binding affinities for low, medium, and high multimers of von Willebrand factor. Semin Thromb Haemost 2002;28:139-48.
  9. Favaloro EJ, Bonar R, Kershaw G, Sioufi J, Hertzberg M, Street A, et al. Laboratory diagnosis of von Willebrand's disorder: Quality and diagnostic improvements driven by peer review in a multilaboratory test process. Haemophilia 2004;10:232-42.
  10. Favaloro EJ. Collagen binding assay for von Willebrand factor (vWF: CBA): Detection of von Willebrand disease (vWD), and the discrimination of vWD subtypes, depends on collagen source. Thromb Haemost 2000;83:127-35.
  11. Nishino M, Girma JP, Rothschild C, Fressinaud E, Meyer W. New variant of von Willebrand disease with defective binding to factor VIII. Blood 1989;74:1591-9.
  12. Rodgers SE, Lerda NV, Favaloro EJ, Duncan EM, Casey GJ, Quinn DM, et al. Identification of von Willebrand disease type 2N (Normandy) in Australia: A cross-laboratory investigation using different methods. Am J Clin Pathol 2002;118:269-76
  13. James P, Lillicrap D. The role of molecular genetics in diagnosing von Willebrand disease. Semin Thromb Haemost 2008;34:502-8.
  14. Keeney S, Bowen D, Cumming A. The molecular analysis of von Willebrand disease: A guideline from UK Haemophilia Centre Doctors' Organisation Haemophilia Genetics Laboratory Network. Haemophilia 2008;14:1099-111