Rapid diagnostic tests (RDTs) are diagnostic assays designed for use at the point-of-care (POC), and can be adapted for use in low-resource settings. An RDT is low-cost, simple to operate and read, sensitive, specific, stable at high temperatures, and works in a short period of time. RDTs are already in use for several neglected diseases.
Overview on RDTs
Rapid diagnostic tests (RDTs) are a type of point-of-care diagnostic, meaning that these assays are intended to provide diagnostic results conveniently and immediately to the patient while still at the health facility, screening site, or other health care provider. Receiving diagnosis at the point of care reduces the need for multiple visits to receive diagnostic results, thus improving specificity of diagnosis and the the chances the patient will receive treatment, reducing dependence on presumptive treatment, and reducing the risk that the patient will get sicker before a correct diagnosis is made. Rapid tests are used in a variety of point-of care-settings—from homes to primary care clinics or emergency rooms and many require little to no laboratory equipment or medical training.
RDTs are particularly important in low-resource settings, where:
- Harsh environmental conditions combined with limited access to electricity and refrigeration preclude the use of sensitive equipment
- Technology, equipment, and training required for more complicated laboratory tests are lacking
- Many patients cannot travel easily to the clinic to follow-up on results that take a long time
RDTs can be especially useful with patient samples that can be collected by minimally trained health personal, such as community health workers.1 Body fluids that can be collected non-invasively, such as nasal swabs, urine, saliva, and tears, are preferred as these are most amenable to collection with only minimal training. However, capillary blood collection techniques, such as those used for malaria RDTs, demonstrate that innovation in sample collection can be used to improve the utility of RDTs in low resource settings.
Rather than one specific type of technology, rapid diagnostic tests can be built in a variety of platforms, each with their own benefits and limitations.2 The vast majority of RDTs in use today for neglected diseases are based on immunoassay technology due to its relative simplicity. These tests generally involve the interaction of a fixed reagent of either target antigen or antibody that is linked to some type of visible detector, that then reacts with a patient sample. Other types of technologies, such as nucleic-acid amplification, may be too expensive and require too much advanced technology to be applicable as a point of care test.
Rapid diagnostic tests have particular value as epidemiological tools, in addition to use as diagnostics. They enable a rapid screening of a potentially affected population, and can be used, as is the case with lymphatic filariasis, as a test of cure to determine when a mass drug administration has been successful. RDTs are less necessary for diseases that are generally accurately diagnosed syndromically, but could prevent over-prescription of antibiotics if used to differentially diagnose fever or diarrhea, respectively.2
P. van Lode (2005). “Point-of-care immunotesting: Approaching the analytical performance of central laboratory methods”. Clinical Biochemistry 38.
Mabey et al. (2004). “Diagnostics for the Developing World.” Nature Reviews Microbiology