Vitamin deficiency tests

Metabolic loading tests and the determination of enzyme saturation with cofactor measure the ability of an individual to meet his or her idiosyncratic requirements from a given intake, and, therefore, give a nearly absolute indication of nutritional status, without the need to refer to population reference ranges. A number of factors other than vitamin intake or adequacy can affect responses to metabolic loading tests. This is a particular problem with the tryptophan load test for vitamin Be nutritional status (Section 9.5.4) a number of drugs can have metabolic effects that resemble those seen in vitamin deficiency or depletion, whether or not they cause functional deficiency. 

Calcium— An essential macro mineral necessary for bone formation and other metabolic functions. Controlled experiment— Also called a controlled trial. The dividing into groups of experimental subjects to see what the effects of a drug will be when tested along with a dummy drug or placebo (a drug other than the one being tested). Dermatitis—An inflammation of the skin. A symptom of vitamin deficiency. 

At One time it was thought that women taking oral contraceptives were at risk for B deficiency. This notion seem-S to have been in error. The error was due to a misinterpretation of the tryptophan load lest. As mentioned earlier, a deficiency in vitamin B(,can induce the accumulation of specific intermediates of the tryptophan catabolic pathway and enhanced excretion in the urine. Oral contraceptives can also induce ar increase in the formation and excretion of specific intermediates by stimulating the activity of specific enzymes of the tryptophan catabolic pathway, This stimulation was responsible for the false indications of deficiency. Independently of the tryptophan load test, there continues to be some evidence for risk associated with the use of oral contraceptives. Oral contraceptive use may result in lowered levels of plasma vitamin Bf, Tlicsc lowered levels may result in a vitamin deficiency when coupled with pregnancy and lactation. 

Folate can be measured in plasma or serum by microbiological assay using L. casei as the test organism, but this test can be confounded if the subject is on antibiotic treatment. Serum folate values reflect recent dietary intake and a vitamin deficiency is ascribed only where serum folate remains low over a period of time. Plasma folate levels are thought to reflect the day-to-day variations in dietary folate levels while red blood cell folate is a better indicator of long-term tissue storage levels. 

The metabolism of methionine, shown in Figure 11.22, includes two pyridoxal phosphate-dependent steps cystathionine synthetase and cystathionase. Cystathionase activity falls markedly in vitamin deficiency, and as a result there is an increase in the urinary excretion of homocysteine and cystathionine, both after a loading dose of methionine and under basal conditions. However, as discussed below, homocysteine metabolism is affected more by folate status than by vitamin status, and, like the tryptophan load test, the methionine load test is probably not reliable as an index of... 

All of the studies that suggested that oral contraceptives cause vitamin deficiency used the tryptophan load test (section 11.9.5.1). When other biochemical markers of status were also assessed, they were not affected by oral contraceptive use. Furthermore, most of these studies were performed using the now obsolete high-dose contraceptive pills. 

Although the FIGLU test depends on folate nutritional status, the metabolism of histidine will also be impaired, and hence a positive result obtained, in vitamin deficiency because of the secondary deficiency of free folate. About 60% of vitamin B -deficient subjects show increased FIGLU excretion after a histidine load. 

Laboratory Tests for Mineral Deficiencies. Tests for iron-deficiency anemia are widely used all over the world but most of the tests for other mineral deficiencies are limited mainly to research studies, because there is a lack of information regarding normal values for such groups as infants, children, adults, and pregnant or nursing mothers. Nevertheless, a growing number of commercial laboratories offer analyses of hair and/or urine directly to customers. These laboratories may also sell mineral and vitamin supplements to the people who use their services. 

In spite of many early investigations with specific nutrient or vitamin deficiencies and protein deprivation in animals showing very significant decreases in antibody responses to a number of test antigens (Scrimshaw et al, 1968), it is not at all well established that major abnormalities occur in the human with PEM. To the extent that specific antibody responses are T-lymphocyte dependent, then altered T-cell maturation will impact upon B-cell function and diminished antibody may result, even though the B-cell system is itself functioning perfectly well,... 

Biological, spectroscopic, and chromatographic methods have been used to assay vitamin A and the carotenoids. Biological methods have traditionally been based on the growth response of vitamin A—deficient rats. The utiUty and shortcomings of this test have been reviewed (52,53). This test has found apphcabiUty for analogues of retinol (54,55). Carotenoids that function as provitamin A precursors can also be assayed by this test (56). 

On a vitamin A-deficient diet, mucus-secreting tissues become keratinized. This condition tends to occur in the trachea, the skin, the saUvary glands, the cornea, and the testes. When this occurs in the cornea, it can be followed by blindness. Vitamin A deficiency is the principal cause of blindness in the very young. This problem is particularly acute in the third world (8). 

Tests to exclude possible causes of dementia include a depression screen, vitamin B12 deficiency, thyroid function tests [thyroid-stimulating hormone (TSH) and free triiodothyronine and thyroxine], complete blood cell count, and chemistry panel.21... 

Vitamin B12 (cyanocobalmin) administered both orally and parenterally is equally effective in treating anemia from vitamin B12 deficiency. However, use of parenteral cyanacobalamin is the most common method of vitamin B12 replacement because it may be more reliable and practical. Subcutaneous or intramuscular administration is appropriate. Vitamin B12 is absorbed completely following parenteral administration, whereas oral vitamin B12 is absorbed poorly via the GI tract. Furthermore, use of parenteral vitamin B12 to treat megaloblastic anemia may circumvent the need to perform a Schilling test to diagnose lack of intrinsic factor. 

Rule out vitamin B]2 and folate deficiency Rule out hypothyroidism with thyroid function tests Blood cell counts, serum electrolytes, liver function tests Other diagnostic tests... 

While the dog is a carnivore, it is able to adapt to an omnivorous diet. Requirements for dietary sources of energy, amino acids, glucose precursors, fatty acids, minerals, vitamins, and water have been established based on recommendations by the National Research Council (NRC, 1985). Adult beagles maintained in a laboratory environment function well with one feeding of standard laboratory chow per day. In safety assessment testing, however, some compounds may induce serious dietary deficiencies through induced loss of appetite, malabsorption, or vomiting, and, in these cases, it may be advisable to provide a dietary supplement. 

In view of the reported growing importance ascribed to folic acid deficiency in the prevention of various disease conditions, such as neural tube defects, megaloblastic anemia, colon cancer, and colorectal cancer, a dissolution requirement is specified for folic acid when it is present in multivitamin-mineral combination products. Currently, the dissolution standard required in the official articles of dietary supplements (including vitamin-mineral combination products) places folic acid outside the index vitamin hierarchy. Therefore, a mandatory dissolution test for folic acid is required that is independent of and in addition to the mandatory index vitamin test for multivitamin preparations containing folic acid. 

The amount of vitamin B6 required by humans is not well established,73 and only recently has evidence been obtained that the needs are variable. Hansen and Bessey74 have found that in some babies 3 or 4 times as much vitamin B6 is needed to prevent the excretion of xanthurenic acid after a test dose of tryptophane than in others. It is these particular babies who develop clinical vitamin B6 deficiency when the intake is low. These findings seem to indicate strongly that some babies have vitamin B6 requirements 3 or 4 times as high as others. 

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