These investigations have a simple yes – no question, is the drug, toxin, or heavy metal there or not? There is also the advantage that most of the metals and toxins looked for have a fairly stable chemical nature. They are un-reactive compared to nutrients so they are less likely to change with exposure to the environment.
With nutrient analysis the laboratory is attempting to define shades of gray – exactly how much of the nutrient is there? This has been shown to be virtually impossible to do. Even sending hair samples from the same donor to different analysis labs yields contrasting results.
Each vitamin and most minerals are present in blood in extremely small concentrations. Blood also contains a great number of chemicals and molecules and many of these tend to interfere with vitamin and mineral tests. For this reason, a procedure like HPLC (high pressure liquid chromatography) that separates the vitamin or mineral from contaminating substances is usually performed prior to conducting the actual test.
Following separation or purification by HPLC, the vitamin or mineral is detected by a color reaction or fluorescence reaction. In these reactions, the amount of color or fluorescence that is formed is proportional to the amount of vitamin or mineral in the sample, allowing the amount of nutrient present in the original sample to be calculated. In the case of some nutrients, the purified factor of interest is reacted with a special chemical (reagent) prior to detection.