Indeed for tests such as cholesterol the idea of a normal range has been replaced to a large extent by use of target values, achieved either by lifestyle changes or active treatment.
Whether or not your test result is within the laboratory reference range, the result must be considered within the context of your personal circumstances, and with the benefit of your doctor's knowledge of your past medical history, current medication and the results of any other investigations.In other words, even in a 'normal' population, a test result will lie outside the reference range in 5% of cases (1 in 20). The first step in determining a reference range is to define the population to which the range will apply. The reference range is then derived mathematically by taking the average value for the group and allowing for natural variation around that value (plus or minus 2 standard deviations from the average). This is why the term 'reference range' is preferred over 'normal range'.
When you examine test results from different populations, you quickly discover that what is 'normal' for one group is not necessarily normal for another group. In this way, ranges quoted by labs will represent the values found in 95% of individuals in the chosen 'reference' group. A large number of individuals from a group who are thought to represent a 'normal' population, will be tested for a particular laboratory test.
A blood test can tell your healthcare provider a lot about your health, from how well you are managing diabetes and high cholesterol to whether or not you have heart disease, cancer, or another condition that has gone undetected for a long time. Then, a report is prepared for your doctor to review. Your healthcare provider will use this information to make a diagnosis and prescribe treatment. It can also help your doctor understand what is causing certain health conditions, and give you an early warning system so that you can take action to improve your condition or prevent it from happening in the first place.Basically, when you have blood drawn at the doctor's office, hospital or laboratory, the blood is processed in a laboratory and is then analyzed for a variety of biomarkers.