Vitamin Tests Health Article

Definition

Vitamins are small organic molecules that are necessary for many biochemical reactions in the body. For example, many vitamins participate as cofactors in enzyme reactions within the cells. They must be obtained through diet, microorganisms in the gut or sunlight since humans cannot synthesize them. Vitamin tests measure the levels of certain vitamins in an individual's blood which can be correlated to the levels of vitamin in their tissues. They are generally used to aid in the diagnosis of vitamin deficiencies or in detecting toxic amounts of a vitamin in a patient's system.

Purpose

Vitamins are components of food that are needed for growth, reproduction, wound healing, digestion of food, blood clotting, bone metabolism and maintaining good health. They can be isolated from plants and organisms or they can be synthesized in the laboratory. The vitamins include vitamin D, vitamin E, vitamin A, and vitamin K, which are the fat-soluble vitamins, and folate, vitamin B₁₂, biotin (vitamin H), vitamin B₆, niacin, thiamin, riboflavin, pantothenic acid, and ascorbic acid (vitamin C), which are the water-soluble vitamins. Fat soluble vitamins are absorbed and transported differently from the water soluble vitamins. They can remain in the body longer since they can be stored in fat so they are more toxic in high doses.

Vitamins are required in the diet in only tiny amounts, in contrast to sugars, starches, proteins and fats. However, vitamin requirements can rise after surgery, with cancer and other illnesses, and during infection and pregnancy. Not receiving sufficient quantities of a certain vitamin can be devastating, resulting in vitamin deficiency diseases such as scurvy (vitamin C deficiency), pellagra (niacin deficiency), megaloblastic anemia (vitamin B₁₂ or folate deficiency) or rickets (vitamin D deficiency). Less extreme deficiencies can cause a delay in wound healing. Conversely, consuming too much of a certain vitamin, especially the fat soluble ones, can be toxic to a person's system. While most vitamin deficiencies are rare in our society, they can be caused by certain diseases, especially those that affect absorption of food, or can be caused by inborn errors of metabolism, fad diets, anorexia, blood loss, parenteral nutrition and dialysis. The vitamins that are most commonly measured by doctors are folate, vitamin B₁₂, vitamin K, vitamin D, and vitamin A.

Precautions

Most vitamin tests are performed on blood samples collected from a vein in the crease of the arm. The nurse or phlebotomist performing the procedure should observe universal precautions for the prevention of transmission of bloodborne pathogens. Some drugs are known to increase or decrease the level of specific vitamins. The physician should obtain a thorough list of the patient's medications when requesting vitamin measurements.

Description

Many of the vitamin tests done today are vitamin status panels, such as megaloblastic anemia panels that measure the concentration of both vitamin B₁₂ and folate. A deficiency of either of these vitamins results in anemia associated with enlarged (macrocytic) red blood cells. The actual testing methods take advantage of the compound's chemical composition. Fat soluble vitamins are measured differently from water soluble vitamins. In general, the tests are performed on plasma, although some tests for metabolites of vitamins can be done on urine, as is the case with many of the water soluble vitamins. Each vitamin occurs at extremely small concentrations in the blood and urine when compared to levels of most other molecules. For this reason, a procedure that separates the vitamin from the rest of the compounds in the sample is usually performed immediately prior to conducting the actual test. This isolation is done using filters that allow the vitamin to pass through and leave the bigger molecules behind. Vitamin B₁₂ and folate are routinely measured by immunoassay methods, but the most common method to measure other vitamins is high-performance liquid chromatography (HPLC). In HPLC, the vitamin to be measured is extracted from the sample and injected into a stream of solvent that is pumped at high pressure through a column packed with particles to which an organic liquid has been bonded. The molecules separate at different rates depending upon their affinity for the bonded particles. The time at which they elute (i.e., come out of the column) is used to identify the molecules. As the vitamins elute, they flow through a detection cell where they are measured by ultraviolet or infrared light absorption or by fluorescence. In these reactions, the amount of light absorbance or amount of fluorescence is proportional to the amount of vitamin in the sample.

While HPLC and immunoassay are the testing methods used most often, other types of tests exist including biochemical (photometric) tests and microbiological assays. Some tests, such as those for riboflavin, are conducted by giving the patient a riboflavin "load" and looking at metabolites in the urine. Vitamin K defiency, a vitamin crucial in blood clotting, is often evaluated by a surrogate test, the prothrombin time. The prothrombin time is measured routinely on patients before they under-go a surgical procedure since long clotting times can complicate surgeries. The test measures how long it takes for a fibrin clot to form in a plasma sample to which calcium and tissue thromboplastin (a clot activator) have