Vitamin B<sub>1</sub>, Plasma
| Vitamin B1, Plasma | | | |
| Number | | 121178 |
| CPT | | 84425 |
| Synonyms | | B1 Vitamin, Plasma ; Thiamine, Plasma |
| Specimen | | Plasma, frozen and protected from light |
| Volume | | 3 mL |
| Minimum Volume | | 2 mL |
| Container | | Lavender-top (EDTA) tube; amber plastic transport tube with amber stopper. (If amber tubes are unavailable, cover standard transport tube completely, top and bottom, with aluminum foil. Identify specimen with patient name directly on the container and on the outside of the aluminum foil. Secure with tape.) For amber plastic transport tube and amber stopper, order LabCorp No 23598. |
| Collection | | Draw blood. Immediately separate plasma from cells. Protect specimen from light. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested. |
| Storage Instructions | | Freeze plasma in plastic transport tube. Protect from light. |
| Causes for Rejection | | Hemolysis; thawed specimen; specimen not protected from light |
| Reference Interval | | 4.0-20.0 μg/L |
| Use | | Thiamine is an essential nutrient for both plants and animals. In plants, it is synthesized in the leaves and is transported to the roots where it controls growth. In animals, thiamine diphosphate plays an essential role in carbohydrate metabolism, and there is growing evidence of its importance also in protein and lipid biosynthesis. Eighty percent of the total thiamine content of blood is found in the erythrocytes, predominantly in the form of the diphosphate. The red blood cell is a good indicator of body thiamine stores, which amount to only about 30 mg, or 30 times the daily requirement. Thiamine deficiency can therefore develop after only 1 month of a thiamine-free diet. Mild thiamine deficiency occurs in pregnant women (increased requirement), and in alcoholics, the elderly, persons who have persistent vomiting or gastric suction, and those who go on long fast (poor intake). Severe thiamine deficiency, called beriberi and characterized by peripheral neuritis or cardiac failure, occurs in Southeast Asia among people who eat polished rice (thiamine deficient diet) and foods rich in antithiamine substances. |
| Methodology | | High-pressure liquid chromatography (HPLC) with fluorescence detector |
| Additional Information | | Thiamine is an important cofactor for the transketolation reactions of the pentose phosphate cycle, which provides pentose phosphate for nucleotide synthesis and for the reduced NADP required for various synthetic pathways. It is possible to assess thiamine nutritional status by measuring the transketolase reaction, but this is a functional rather than a direct test. Transketolase assay is relatively insensitive and is dependent upon the hemoglobin concentration. In addition, the transketolation reaction can be influenced by factors other than thiamine deficiency, such as reduction of apoenzyme synthesis, impaired phosphorylation of thiamine, or reduced binding of apo- and coenzyme. Recently, the use of HPLC for direct quantitation of thiamine has provided the sensitivity and specificity necessary for clinical evaluation of thiamine nutritional status. Although thiamine can be measured in plasma, erythrocytes, or whole blood, it is usually measured in whole blood. |
| References | | Cheng KS and Chou PP, “Measurement of Total Thiamine in Whole Blood, RBC, and Plasma by HPLC With Fluorometric Detection,” Clin Chem, 1988, 34(6):1308. Kawasaki T, Modern Chromatographic Analysis of Vitamins, 2nd ed, Volume 60, New York, NY: Marcel Dekker, Inc, 1992, 319-54. “Thiamine,” Tietz Textbook of Clinical Chemistry, Philadelphia, PA: WB Saunders Co, 2nd ed, 1994, 1277, 1290-6. |
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