Phenotype describes the set of observable characteristics of an individual (for example, hair colour, height, and behaviour). In the case of VWD, an example of a phenotypic characteristic may be the capacity of an individual’s von Willebrand factor (VWF) to bind factor VIII (FVIII). The term genotype refers to the genetic makeup of an individual, and the underlying genetic reason for a phenotype. For example, defects (mutations) or missing pieces (deletions) in the VWF gene may affect the binding of VWF to FVIII, and these abnormalities may be detected by molecular diagnostic techniques. These two articles review current approaches to diagnosing VWD by looking at the phenotype or the genotype of the patient.
In VWD, the diagnostic approach begins with the clinical assessment of a person with bleeding symptoms and a positive family bleeding history. TOH 55 Diagnosis of von Willebrand Disease: Phenotypic Characterization examines four key areas: an overview of VWD diagnosis, phenotypic diagnosis, classification of VWD, and diagnosis of VWD in low resource countries. TOH 55 guides the clinician or laboratory specialist through a sequence of increasingly specific laboratory tests necessary for an accurate diagnosis of VWD. The table below describes the uses and limitations of tests referred to as first and second level tests, and explains what these are. The article highlights why these tests are performed and how they are interpreted. In addition, each technique is linked to its corresponding detailed protocol in the WFH Laboratory Manual on the WFH eLearning Platform.
USE OF LABORATORY TESTS FOR PHENOTYPIC DIAGNOSIS OF VWD