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Infectious disease markers are biological indicators used to identify infections, determine their cause, evaluate disease activity, and monitor treatment response. They may include antigens, antibodies, nucleic acids, inflammatory proteins, and changes in blood cell counts. Selecting the appropriate marker depends on the suspected pathogen, stage of infection, and clinical presentation.

Antigen tests detect specific components of microorganisms and can provide rapid evidence of active infection. Antibody tests identify the immune response produced against a pathogen. Immunoglobulin M (IgM) commonly suggests recent exposure, while Immunoglobulin G (IgG) may indicate previous infection or developing immunity, although interpretation varies among diseases. Molecular markers, particularly pathogen-specific DNA or RNA detected through polymerase chain reaction (PCR), can identify infections with high sensitivity and specificity.

Inflammatory markers such as C-reactive protein (CRP), procalcitonin, and erythrocyte sedimentation rate may support assessment of systemic inflammation, although they generally cannot identify a specific pathogen alone. Microbiological culture remains important for detecting viable organisms and determining antimicrobial susceptibility.

Accurate interpretation requires correlation with symptoms, examination findings, exposure history, and other laboratory investigations. Understanding infectious disease markers helps healthcare professionals achieve timely diagnosis, select appropriate treatment, monitor progression, and reduce unnecessary antimicrobial use and complications.