Disease blood biomarkers are defined as measurable indicators in blood circulation reflecting physiological, pathological, or therapeutic states. Blood biomarkers are playing a dual transformative role in modern healthcare: as clinical tools for diagnosis and management and as predictive forensic evidence in legal and regulatory contexts. This chapter will examine their application across both communicable (e.g., viral hepatitis, COVID-19) and noncommunicable diseases (e.g., cardiovascular disease, diabetes, cancer), highlighting their evolving forensic utility. In communicable diseases, blood biomarkers enable early detection, severity stratification, and monitoring of viral dynamics. For hepatitis B, markers such as HBsAg, HBeAg, and HBV DNA quantify infection status and viral load, while anti-HDV IgM and HDV-RNA confirm hepatitis D co-infection. From a forensic perspective, these biomarkers can: validate occupational disease claims, substantiate medical negligence allegations (e.g., delayed myocardial infarction diagnosis); support insurance or disability determinations (e.g., chronic kidney disease progression); and inform regulatory actions regarding drug safety or environmental hazards. Ultimately, blood biomarkers represent a powerful interface between medicine and law: they translate biological signals into actionable evidence, improving patient outcomes while advancing fairness and accountability in forensic contexts.