Folate FIGLU test

Figure 10.6. Catabolism of histidine - basis of the FIGLU test for folate status. Histidase, EC 4.3.1.3 urocanase, EC 4.2.1.49 FIGLU formiminotransferase, EC 2.1.2.5. THF, tetrahydrofolate.

The ability to metabolize a test dose of histidine provides a sensitive functional test of folate nutritional status as shown in Figure 10.6, forrnirninoglu-tamate (FIGLU) is an intermediate in histidine catabolism and is metabolized by the tetrahydrofolate-dependent enzyme FIGLU forrnirninotransferase. In folate deficiency, the activity of this enzyme is impaired, and FIGLU accumulates and is excreted in the urine, especially after a test dose of histidine - the FIGLU test. 

Although the FIGLU test depends on folate nutritional status, the metabolism of histidine wUl also be impaired and a positive result obtained, in vitamin B12 deficiency, because of the secondary deficiency of folate (Section 10.3.4.1). About 60% of vitamin Bi2-deficient subjects show increased FIGLU excretion after a histidine load. 

CataboUsm of histidine - basis of the FIGLU test for folate status. 282... 

Folate deficiency leads to accumulation of Figlu, which is excreted in urine. The excretion is very pronounced after a loading dose of histidine, a test used to detect folate deficiency. More sensitive radioisotopic assays use folate binders to the vitamins. High urinary levels of Figlu may coexist with elevated levels of serum folate. Thus, in vitamin Bn (cobalamin) deficiency, since cobalamin participates in the following reaction, FH4 is trapped as... 

A deficiency of folate results in the accumulation of FIGLU, which is excreted in the urine. A histidine load test can be used for detecting folate deficiencies. Patients were given a test dose of histidine (a histidine load), and the amount of FIGLU that appeared in the urine was measured. 

An in vivo test for the investigation of suspected folic acid deficiency. The normal metabolism of histidine contains a step in which formiminoglutamic acid (FIGLU) is converted to glutamate by an enzyme which uses folate as a cofactor. In patients with folate deficiency, administration of oral histidine results in a greater than normal urinary excretion of FIGLU. 

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