It is not possible to detect the disease early using traditional methods of treatment (serum and urine analysis etc.). But in the modern medical system, recombinant DNA technology, polymerase chain reaction (PCR), enzyme linked immunosorbent assay (ELISA) etc. are some of the techniques through which the diseases can be identified early.
The disease is not detected in its initial stages, but when the numbers of disease causing agents (bacteria, viruses etc.) increases in the body, then the symptoms of that disease become visible. When there is very less number of pathogens in a person's body, then symptoms of the disease are not visible. But now they can be identified initially by amplification in their nucleic acid by PCR. PCR is also used to detect gene mutations in suspected cancer patients. PCR is a commonly used method for HIV detection in suspected AIDS patients.