Normal ranges on any type of labwork are determined by the company that manufactured them. There are different tests even in the same country with very different ranges of normal. There are many different types or brands of blood hormone tests. When a manufacturer designs the lab test, it sets up the test by using it on samples with known values of hormone. So tube one has a level of 10, tube two level 20, tube three level 50, etc. The test is run, and each tube gives a specific number. These results are plotted on a graph. Later, when an unknown sample is tested, the result is measured against the graph to determine the level of hormone in the test sample. Theoretically, we should get reasonably similar results when your blood sample is sent to different labs. But it is not that simple. Remember we started with tubes with known hormone amounts -- 10, 20, 50? These tubes are called "hormone standards." Since all blood tests compare your sample against other known samples, we rely on these standards to be truly similar between different brands of the test. Unfortunately, they are not. So what is considered 10ng/ml of prolactin in one test's standard may not be similar to 10ng/ml in another test. Yes, it is confusing. The result is that one test brand may indicate one value, while a different test may return a value that is quite different. So if I send your blood to 10 different labs, I will most likely get 10 different results that may vary as much as 100 percent. So what this means is that no one can compare their test results to another persons unless you know that the same test was used. |
