1. Screening: They can detect diseases or conditions in their early stages, often before symptoms appear. For instance, cholesterol levels can indicate the risk of heart disease.

2. Diagnosis: Doctors use blood tests to confirm or rule out suspected conditions based on symptoms, medical history, or physical exams. For example, blood tests help diagnose anemia, diabetes, infections, and various organ dysfunctions.

3. Monitoring: Blood tests track the progress of ongoing treatments or chronic conditions. They help doctors adjust medications, assess the effectiveness of treatments, and manage conditions like diabetes, hypertension, or thyroid disorders.

4. Preventive Care: Routine blood tests can be part of preventive healthcare, helping to identify health risks early, promoting lifestyle changes, and preventing diseases before they become severe.