Regarding blood tests, please understand that:
- There are different types of blood-test panels. Some are more extensive than others.
- The two main types of blood test panels are the ones used typically for annual physical exams. These are:
- Serum chemistry panels, otherwise known as CHEM 8, CHEM 15, CHEM 25, etc, depending on how many tests the machine is programmed to handle. These are also sometimes called, Basic Metabolic Panel, Comprehensive Metabolic Panel, etc. When reviewing your bloodwork it is important to notice which kind of panel the doctor has requested, because these panels do not test for everything. If all of your bloodwork tests turn out to be normal, there still might be a problem because your particular panel might not be testing for a particular area where you do indeed have a problem.
- CBC (Complete Blood Count) panels, including CBC+differential. These panels test whether or not your blood cells are functioning as expected.
What you get depends on what the specific panel is designed to deliver. And there is always the possibility of adding extra, specialized tests that are not included in any of the default panels. For example, you may have to request a thyroid test specifically if your default panel does not include any thyroid tests and you need thyroid monitoring. The tests that you mentioned, "Anion gap test" and the "Red Blood Cell Distribution Width (RDW) test" fall in this area: They are specific tests that the doctor wants to do in order to check on something that is not in one of the ordinary blood-test panels. You would have to ask the doctor why he needed to have the information provided by these tests.
Then there are other blood tests that fall in the genetics area. These tests will test for specific mutations that are present in the DNA in all cells of your body from birth. These tests are done mainly to check on inherited DNA mutations that are passed on from one generation to another and are present at birth in all cells of the body. These are tests like the Hereditary Non-Polyposis Colon Cancer (HNPCC) test for Lynch syndrome, and the Familial Adenomatous Polyposis (FAP) test. These tests are not ordinarily done unless there is evidence of a family history of colon cancer.
Then there are the new Circulating Tumor DNA (ctDNA) tests that are designed to detect fragments of tumor DNA that are now circulating in the blood stream. These tests are done for early warning of metastases that may be developing but that are not yet visible on any scans. They are rather expensive and may not be covered by insurance. Then there are the other genetic tests that test for a whole range of possible DNA mutations, like the Foundation One tests, but they, too, are extremely expensive and are probably not worth the cost except in very special cases.