Why is blood tested for diseases?

Blood can be tested for diseases for a number of reasons:

Detection: Blood tests can detect the presence of infectious diseases, such as bacteria, viruses, and parasites. This can be done by looking for the presence of antibodies, which are proteins produced by the immune system in response to infection. Blood tests can also detect the presence of antigens, which are molecules on the surface of infectious agents.

Diagnosis: Blood tests can help diagnose a wide range of diseases and conditions, such as cancer, diabetes, heart disease, and kidney disease. This is done by measuring the levels of specific substances in the blood, such as hormones, enzymes, and other proteins. Abnormalities in the levels of these substances can indicate the presence of a particular disease or condition.

Monitoring: Blood tests can be used to monitor the progression of a disease or condition and to assess the effectiveness of treatment. For example, blood tests can be used to monitor the levels of blood sugar in people with diabetes, or to monitor the levels of white blood cells in people with cancer.

Screening: Blood tests can be used to screen for certain diseases or conditions in people who do not have any symptoms. This can help detect diseases early on, when they are more likely to be curable. For example, blood tests can be used to screen for high blood pressure, cholesterol, and certain types of cancer.