Erythrocytic folate levels

It is of paramount importance to rule out vitamin B12 deficiency when folate deficiency is detected, as symptoms are similar. Laboratory changes associated with folate deficiency are similar to those seen in vitamin Bn deficiency, except vitamin Bn levels are normal. Decreases occur in the serum folate level (<3 ng/mL) within a few days of dietary folate limitations. The RBC folate level (<150 ng/mL) also declines and may be a better indicator of deficiency, as levels remain constant throughout the life span of the erythrocyte. Serum folate levels are sensitive to short-term changes such as dietary restrictions or alcohol intake, which may result in a short-term decline in serum levels with adequate tissue stores. It should be noted that an estimated 60% of patients with pernicious anemia have falsely low RBC folate levels, in all probability due to the requirement of cobal-amin for the normal transfer of methyltetrahydrofolate from plasma to cells. Additionally, if serum or erythrocyte folate levels are borderline, serum homocysteine is usually increased with a folic acid deficiency. If serum MMA levels are also elevated, vitamin B12 deficiency needs to be ruled out. 

Davis et al. found that folate was not the only B group vitamin which was reduced in patients receiving treatment with anticonvulsant drugs (D4). In a study of 68 patients suffering from severe epileptic seizures they found that 18 patients had a low folate, 10 a low serum pyridoxal, and in 15 both the folate and pyridoxal were reduced. Only two patients in this series had a reduced erythrocyte folate, and this is in accord with the infrequency with which a macrocytic anemia is seen in these patients. All the patients in this series had a normal hemoglobin concentration and a normal mean corpuscular volume. However, in a study of 75 epileptic children Maxwell (M3) found both the serum and erythrocyte folate levels to be reduced in 60% and similar observations have been made by other workers (M4, N2). 

V2. Vatanavicham, S., Anuvatanakulchai, M., Na-Nakorn, S., and Wasi, P., Serum erythrocyte folate levels in thalassaemic patients in Thailand. Scand. J. Haematol. 22, 241-245... 

The importance of red cell folate determinations in certain diagnoses of folate deficiency has been clearly established. Erythrocyte folate levels are good indicators of tissue folate stores, whereas serum folate levels are poor indicators since they reflect recent dietary intake and often provide little useful clinical information 37-34). For example, serum folate levels fall promptly after transient periods of dietary deprivation and remain abnormally low for weeks or months before red cell folate levels fall. In contrast, the fall in red cell folate immediately precedes the clinical and hematologic manifestation of folate deficiency (42). 

To determine erythrocyte folate levels by the RMA, one volume of heparinized blood was hemolyzed in nine volumes of deionized water. An equal volume of 0.05M phosphate buffer, pH 6.1, containing 200 mg % of ascorbic acid was added to the hemolyzed blood. Since erythrocyte folate is mainly reduced polyglutamates, this hemolysate was incubated at 37°C for 20-30 min in order for plasma conjugase to reduce the glutamic acid residues to the extent necessary for their utilization by L. cdsei (44). After incubation, the hemolysate was further diluted and assayed as described (26). 

Table VIII. Radiometric Microbiological Assay Reproducibility of Erythrocytic Folate Levels (26)...

Table 28.3 Homocysteine metabolism parameters in preeclampsia. Data expressed as median (interquartile range). Serum and erythrocyte folate levels not reported because these were within relevant reference interval in both groups. Data are from a study by our group.

Plasma homocysteine Urinary excretion Blood levels Urinary excretion Erythrocyte folate... 

One patient has been found with this deficiency (All). Hie patient, an infant, was mentally retarded, had a megaloblastic anemia and abnormally high levels of serum and erythrocyte folate. In spite of the high serum folate concentration there was a marked rise in the reticulocyte count when the patient was treated with folate. It was thought that the patient had impaired utilization of -methyltetrahydrofolate. Assay of liver W -methyltetrahy-drofolate transferase showed it to be reduced. It was suggested that folate accumulated at the N -methyltetrahydrofolate block and could therefore not be further utilized. Treatment with pteroylglutamic acid provided a means of producing active folate up to the point of the block. Unfortunately this patient was also treated with pyridoxine, and it is not clear which vitamin was responsible for the reticulocyte response. Further studies are required to determine the precise nature of this metabolic disorder. 

There have been other single reports of megaloblastic anemia associated with an apparent abnormality of folate metabolism. One child had a normal serum folate of 6 p,g/liter, an erythrocyte folate of 1480 p.g/liter, and a megaloblastic anemia which responded to treatment with folic acid (VI). Lampkin (Lll) described two sisters with a severe megaloblastic anemia and normal vitamin 6 2 folate levels. Absorption of vitamin 6, 2 normal and both patients excreted an increased amount of formiminoglutamic acid. It was thought that they required both vitamin B 2 and folate to restore normoblastic hemopoiesis. 

Varadi and Elwis (V3) found low erythrocyte folates in 10 of 81 hospital patients over the age of 70 years. They were suffering from a variety of disorders which included senile dementia, cerebral thrombosis, and arthritis. None had a megaloblastic anemia. Thirty nine percent of ed people admitted to the hospital in the London area were found to have a low serum folate (H29). Read (R15) in another study found that 40 (78%) of 51 people admitted to an old peoples home were folate deficient with a serum concentration below 6 p,g/liter and in three the concentration was below 3 Xg/liter. In an apparently healthy control group of similar age all had levels... 

Low levels of serum folate are often associated with low levels of erythrocyte folate (intracellular). The mean corpuscular volume (MCV) of erythrocytes may increase slightly with low folate levels, though overt macrocytic anaemia occurs infrequently. Carbamazepine (CBZ) therapy may cause leukopenia and neutropenia. In a randomized trial in patients on CBZ, subjects on folic acid had higher leucocyte counts and less neutropenia compared with subjects without vitamin supplements. Other studies found no connection between folate and AED-induced haematological abnormalities. 

There are several vitamin Bg-responsive inborn errors of metabolism that include (1) cases of infantile convulsions in which the apoenzyme for glutamate decarboxylase has a poor affinity for the coenzyme (2) a type of chronic anemia in which the number but not morphological abnormality of erythrocytes is improved by pyridoxine supplementation (3) xanthurenic aciduria in which affinity of the mutant kynureninase for PLP is decreased (4) primary cystathion-inuria caused by similarly defective cystathionase and (5) homocystinuria in which there is less of the normal cystathionine synthetase. In these cases increased levels (200 to lOOOmg/day) of administered vitamin Bg are required for life. Low vitamin Bg status (together with low vitamin B12 and folate status) in humans has been linked to hyperho-mocysteinemia and as an independent risk factor for cardiovascular disease. ... 

The resnlts of folic acid measnrements may vary depending on the assay method nsed. Decreased serum folic acid levels indicate a folate deficiency megaloblastic anemia that may coexist with a vitamin B12 deficiency anemia. An erythrocyte folic acid level is less volatile than sernm levels, as it is slow to decrease in an acnte process such as drug-induced folic acid deficiency, and slow to increase with oral folic acid replacement. However, the clinical ntflity of determining the erythrocyte folic acid level is qnestionable, and the procedure should be reserved for cases in which the clinician snspects folic acid depletion and the serum folic acid may be falsely elevated or depleted. 

Folate deficiency results in megaloblastic anemia. Megaloblastic anemia is characterized by macrocytic erythrocytes produced by abnormal proliferation of erythroid precursors in the bone marrow. Folate deficiency encumbers the maturation of these cells by inhibition of DNA synthesis. Without an adequate supply of folate, DNA synthesis is limited by decreased purine and dTMP levels. 

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