A blood test is an extremely useful source of information about the health of a body. Because blood is affected by many medical conditions, the shape, size, behaviour, and numbers of blood cells reveal a lot, so blood tests are used to form diagnoses, and to monitor illness and the effectiveness of treatment. A blood test is fast, safe, and fairly reliable. Some tests can be done with only a drop of blood, whereas others may need a lot more. Blood tests give information about such thing as blood chemistry, kidney and liver function, hormone, cholesterol and glucose levels, and numbers of antibodies.
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What is blood affected by?