Question

Visceral leishmaniasis has a very high case fatality rate but is difficult to diagnose: bone marrow biopsy, one of the best diagnostic methods, is expensive and is often associated with serious side effects. If you were developing a new diagnostic for this disease, would you be more interested in maximizing sensitivity or specificity? Also, assuming your new test is cheaper and less invasive than biopsy, would you advocate that it be used in conjunction with (ie simultaneously) or prior to (ie sequentially) the invasive diagnostic test? What factors would go into this decision?

Answer 1

Visceral leishmaniasis is also called kala-azar. This disease is caused by a protozoan parasite, a Leishmania species. The protozoa travelled inside the body in the organs like liver, spleen or bone marrow. This is the reason, the disease is called visceral.

As the best method to detect the disease is bone marrow biopsy, the method is expensive, have side effects and also not availbale to part where the disease is more widespread. So there is a requirement for alternative detection method which will be rapid, less expensive and non-invasive.

So if I'm developing a new diagnostic method then I would be interestes more in specificity than sensitivity. Because the main purpose of the diagnosis is whether the parasite is present in the body or not. For instance, if there leishmaniasis antigen or anti- leishmaniasis antibody in present , we can presict that the person might get infeced by leishmania. In this case sensitivity will only measure the amount of antigen or antibody present.

If the new test is cheaper and less invasive than biopsy hen I will recommend to use the method prior to invasive diagnostic test. If the method is able to confirm the presence of Leishmaniasis then there will be no need for more challenging invasive methods, as it will have side effect also.