Which one of the following techniques is not used for early diagnosis…

The correct answer is Option (3) → Serum analysis

A disease can be treated well only if it is found early, before symptoms show. By the time a pathogen causes symptoms, it is already present in large numbers. Conventional tests cannot find it earlier, so molecular methods are used.

(1) ELISA — Used for early diagnosis. ELISA (enzyme linked immuno-sorbent assay) detects the antigens of the pathogen, or the antibodies made against it, by an antigen-antibody reaction.

(2) Recombinant DNA technology — Used for early diagnosis. A probe made by this technology can find the pathogen’s gene.

(3) Serum analysis — Not used for early diagnosis. It is a conventional method (like urine analysis) and cannot detect a disease early.

(4) PCR — Used for early diagnosis. PCR (polymerase chain reaction) amplifies the nucleic acid of a bacterium or virus, so even a very small number of them can be detected before symptoms.

Note: The same question was also asked in CUET (UG) 2025 on 14-05-2025 (Slot 1).

NCERT Extract:
Molecular Diagnosis – “… You know that for effective treatment of a disease, early diagnosis and understanding its pathophysiology is very important. Using conventional methods of diagnosis (serum and urine analysis, etc.) early detection is not possible. Recombinant DNA technology, Polymerase Chain Reaction (PCR) and Enzyme Linked Immuno-sorbent Assay (ELISA) are some of the techniques that serve the purpose of early diagnosis.”