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Thiamin (vitamin B1) is an essential vitamin required for carbohydrate metabolism, brain function, and peripheral nerve myelination. Thiamin is obtained from the diet. Body stores are limited and deficiencies can develop quickly. The total thiamin pool in the average adult is about 30 mg. An intake of 0.5 mg per 1,000 kcal per day is needed to maintain this pool. Due to its relatively short storage time, marginal deficiency can occur within 10 days and more severe deficiency within 21 days if intake is restricted.
Approximately 80% of all chronic alcoholics are thiamin deficient due to poor nutrition. However, deficiency also can occur in individuals who are elderly, have chronic gastrointestinal problems, have marked anorexia, are on cancer treatment, or are receiving diuretic therapy.
The signs and symptoms of mild-to-moderate thiamin deficiency are nonspecific and may include poor sleep, malaise, weight loss, irritability, and confusion. Newborns breast fed from deficient mothers may develop dyspnea and cyanosis; diarrhea, vomiting, and aphonia may follow. Moderate deficiency can affect intellectual performance and well-being, despite a lack of apparent clinical symptoms.
Severe deficiency causes congestive heart failure (wet beriberi), peripheral neuropathy (dry beriberi), Wernicke encephalopathy (a medical emergency that can progress to coma and death), and Korsakoff syndrome (an often irreversible memory loss and dementia that can follow). Rapid treatment of Wernicke encephalopathy with thiamin can prevent Korsakoff syndrome. Symptoms of dry beriberi include poor appetite, fatigue, and peripheral neuritis. Symptoms of wet beriberi include cardiac failure and edema. Patients with Wernicke encephalopathy present with behavior change (confusion, delirium, apathy), diplopia (often sixth nerve palsies), and ataxia. A late stage, in which the patients may develop an irreversible amnestic confabulatory state, is referred to as the Wernicke-Korsakoff syndrome.
The response to thiamin therapy in deficient patients is usually rapid. Thiamin deficiency is a treatable, yet under diagnosed, disorder in the United States. A heightened level of awareness of the possibility of thiamin deficiency is necessary to identify, intervene, and prevent thiamin deficiency's dire consequences. It appears that no conditions are directly attributable to thiamin excess and that thiamin administration is safe except in extremely rare cases of anaphylaxis from intravenous thiamin.
Whole blood thiamin testing is superior to currently available alternative tests for assessing thiamin status. Serum or plasma thiamin testing suffers from poor sensitivity and specificity, and <10% of blood thiamin is contained in plasma. Transketolase determination, once considered the most reliable means of assessing thiamin status, is now considered an inadequate method. The transketolase method is an indirect assessment. Since transketolase activity requires thiamin, decreased transketolase activity is presumed to be due to the decrease of thiamin. However, the test is somewhat nonspecific, as other factors may decrease transketolase activity. Transketolase is less sensitive than HPLC, has poor precision, and specimen stability concerns.
Thiamin diphosphate is the active form of thiamin and is most appropriately measured to assess thiamin status. Thiamin diphosphate in circulating blood is present in erythrocytes, but is undetectable (present in very low levels) in plasma or serum. HPLC analysis of thiamin diphosphate in whole blood or erythrocytes is the most sensitive, specific, and precise method for determining the nutritional status of thiamin and is a reliable indicator of total body stores. This assay specifically targets and quantitates the active form of vitamin B1 (thiamin diphosphate) as an indicator of vitamin B1 status.
Assessment of thiamin deficiency
Thiamin measurement in patients with behavioral changes, eye signs, gait disturbances, delirium, and encephalopathy; or in patients with questionable nutritional status, especially those who appear at risk and who also are being given insulin for hyperglycemia
Values for thiamin diphosphate <70 nmol/L are suggestive of thiamin deficiency.
Vitamin supplementation and non-fasting specimens may result in elevated thiamin diphosphate concentrations.
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