A method of determining whether an individual is infected with mycobacteria. The method comprising the steps of (a) providing a system which comprises at least two different mycolic- acid derived antigens; (b) introducing a sample obtained from the individual into the system and into contact with each of the at least two different mycolic-acid derived antigens; and (c) detecting the presence or absence of the binding of a biomarker in the sample with each antigen in the system. The method may be particularly suitable for determining the presence or absence of a disease antibody indicative of infection with any disease caused by infection with mycobacteria, for example tuberculosis, leprosy, pulmonary disease, burili ulcer, Johne's disease and bovine tuberculosis. A kit and device are also described. The present invention may provide an over the counter device to allow individuals to check on a routine basis that they have normal immune responses.