Final answer:
Blood tests are conducted for a variety of reasons, including diagnosing specific medical conditions, determining blood type for transfusions, and checking cholesterol levels. Measuring blood pressure is not done through blood tests but with physical examinations.
Step-by-step explanation:
A patient may be given a blood test for various reasons, and depending on the type of test, the purposes can vary significantly. Some blood tests, like those that measure lipid or glucose levels in plasma, determine which substances are in blood and in what quantities. These tests are critical for diagnosing specific medical conditions, for example, diabetes mellitus through blood glucose estimation. Measurements of blood pressure are not the objective of blood tests but rather physical examinations performed using a sphygmomanometer.
Other blood tests check for the composition of the blood itself, such as blood type during cross-matching before a transfusion. Another purpose could be to determine the patient's cholesterol levels, like LDL and HDL, which are important indicators for cardiovascular risks. Determination of the right blood type is significant to ensure a patient receives a compatible blood transfusion, and cholesterol levels can indicate risk factors for heart diseases or strokes.