Laboratory diagnosis of leishmaniasis remains a major challenge, demonstrating variable efficacy in detecting infected mammalian hosts. Thus, there is a great need for the accuracy of the identification of appropriate antigens to also improve diagnostic tests. This review brings to the fore the sensitivity of the balance in canine and human leishmaniasis, which greatly influences the progression of the disease and especially the diagnostic methods. The problem of diagnosis arises in asymptomatic leishmaniasis, since in these conditions the methods considered as reference in the diagnosis of leishmaniasis no longer show certainty, being influenced for the most part by the immune response of the host, which is different according to the presence of other associated diseases or even according to the breed, when we talk about dogs. Consequently, the diagnosis and surveillance of leishmaniasis cases remains an open topic, with the need for new methods adapted to the immunological status of the host.