Many different inherited bleeding disorders have been identified in dogs, defined on the basis of quantitative, functional, or structural defects in specific hemostatic proteins or pathways. Most of these disorders are caused by single-gene defects and biochemical assays provide an accurate measure of disease phenotype. Phenotypic disease classification, however are often genetically heterogeneous. Protein-based carrier detection assays are fast, inexpensive, and do not require specific identification of causative mutations. The limitations of these tests arise from variable 'overlap' regions between carrier and clear dogs, influencing positive and negative predictive values of carrier detection tests within breed populations. Molecular diagnostic techniques enhance the accuracy of carrier detection, providing their clinical application takes into account the molecular heterogeneity underlying naturally occurring hemostatic defects in dogs.