There is a medical book called the MERCK MANUAL. It lists normal values for hundreds of commonly used tests. On that list is a joke for nerds. The MERCK MANUAL lists a normal for serum porcelain level. So according to this book, you can literally be tested for everything including the kitchen sink. I think that is hilarious. I know that I am in a tiny minority.
Most doctors who do primary care run the same screening tests as a matter of routine. We all do similar things because we all agree that this is one thing that we should do to keep our patients healthy. One is a CBC or Complete Blood Count. It is a count of all of the different types of cells in the blood. Chemistry is another. It reflects the amounts of different salts and other substances dissolved in the blood. We also do other more specific testing for people who are at risk for certain problems like elevated cholesterol, diabetes, vitamin deficiencies or toxins, etc. We can’t check the thousands of available tests for everything and the kitchen sink. That would be quite expensive and truly unnecessary.
A blood test by itself does not make a diagnosis. For example, many people are screened for an underactive thyroid gland. They get a TSH level. The thyroid gland makes a hormone which is like a gas pedal for the body. It tells most systems in the body to keep running at speed. Without it, we end up without the energy to do anything. We sleep for hours more than normal, gain weight, feel terrible and can even have heart problems. Most of the time, the test serves its purpose and the result matches the symptoms of the patient. Sometimes, however, the test result is normal even when the patient has all of the symptoms of a low thyroid hormone level. The more specific confirmatory tests can also be normal. This condition has a name, euthyroid sick syndrome. It means that despite the normal test results, the person needs more thyroid hormone anyway.
So why do we do blood tests if not to make a diagnosis? They are useful because a lot of different diseases end up affecting the results of few basic blood tests like the CBC and Chemistry. This can give us a clue that something is happening. Then we can then talk to and examine the patient and sometimes order other tests to try to figure out more precisely what, if anything, is going wrong. Sometimes we order tests to “rule out” a condition, to make sure that a patient does not have a problem. In reality, a diagnosis is not made by a single blood test. Rather, the diagnoses are made through the understanding of symptoms, physical exam and testing.
Running tests is your doctor’s way of making sure that you are OK and there are no diseases trying to sneak up on you. They are trying to get a recommended amount of information about you while not racking up a huge bill or literally bleeding you dry. If you have questions about what you are being tested for, there is no harm in asking. It is my belief that if I can’t give a person a reason for any action that I am taking, I should not be doing it. Your doctor should be able to take a moment and explain it to you so that you understand. That way we are all working toward the same goals.