This category brings together diagnostic and monitoring tests designed for specific diseases and medical conditions. Each article explains why the test is ordered, what it measures, how samples are collected, typical reference ranges, and how results are interpreted in the context of disease management. Covering conditions such as diabetes, thyroid disorders, cardiovascular disease, infections, liver and kidney disease, and more, these guides help patients, students, and healthcare professionals clearly understand how each investigation supports diagnosis, treatment, and follow-up.