Determination of riboflavin and flavocoenzymes in human blood plasma by high-performance liquid chromatography

A high-performance liquid chromatographic method for determining riboflavin, flavin adenine dinucleotide, and flavin mononucleotide in human blood plasma is presented. Flavocoenzymes are determined as flavin mononucleotide after acid hydrolysis of flavin adenine dinucleotide. Metabolites are separated by reversed-phase column chromatography and quantified by their native fluorescence. Criteria of quality are (riboflavin/flavocoenzymes): coefficients of variation 2.8/4.6% (intra-assay) and 2.8/4.4% (inter-assay); recovery 82.4/94.4%; detection limit < 3.0/9.0 nmol/l. Because sample preparation requires only few steps, and the retention times are short ( < 5 min), this method is recommended for use in routine analysis.

Fluorometric riboflavin titration in plasma by riboflavin-binding apoprotein as a method for vitamin B2 status assessment

A method for plasma riboflavin determination by riboflavin-binding apoprotein titration has been proposed for vitamin B2 status evaluation. The method is based on the formation of riboflavin-apoprotein complex accompanied by full loss of fluorescence peculiar to free riboflavin. The data obtained have demonstrated a correlation with indicators of the vitamin B2 status such as urinary excretion, erythrocyte content, and stimulation of the glutathione reductase activity by flavin adenine dinucleotide. Levels > 6 ng/ml blood plasma may be considered to be a criterion for normal vitamin B2 supply.

[Refining criteria for providing adults and 12-14 year old children with vitamins B1 and B2]

Analysis of many-year people vitaminization with thiamine showed that middle values of the TDP-effect were not always decreased down to the level of < or = 1.15. The TDP-effect not exceeding 1.25 value should be recommended as a criterion of normal vitamin B1 consumption as followed from mathematical analysis of the correlation between excretion of thiamine with urine and the TDP-effect value as well as from plotting and mathematical interpretation of the variation curves involving distribution of the TDP-effect value among people with additional vitaminization. The literature available data equal to 1.15 appears to exhibit the optimum rate of the vitamin consumption. Excretion of thiamine with urine more than 12 mg/h should be also considered as a normal consumption of vitamin B1 in children of 12 years old and older and in adults. The criteria of vitamin B2 consumption in children of this age were similar to corresponding patterns of adults: minimal concentration of riboflavin in blood plasma was about 6 ng/ml and its excretion with urine--about 14 mg/h.

[Refining criteria for providing the body with vitamin B2]

The following patterns should be recommended as a criterion of normal vitamin B2 requirements: the FAD-effect is no more than 1.25, the levels of riboflavin, more than 5 ng/ml in the plasma and more than 130 ng/ml in the erythrocytes. At the same time, the hourly urinary riboflavin excretion more than 10 g/h may be used as a criterion of normal vitamin B2 requirements in children of 5-7 years old. These values were obtained while analysing the many-year experimental data on riboflavin treatment and using the mathematical analysis of the dependence curves for the urinary riboflavin excretion, its levels in plasma and erythrocytes, and the value of the FAD effect, as well as deriving and mathematically interpreting the variation curvers for the distribution of the given value of the FAD effect and the plasma riboflavin levels for human beings after additional vitamin therapy.

[Isolation of riboflavin-binding apoprotein from chicken egg protein and its use for determining riboflavin in biological samples]

A riboflavine-binding protein has been isolated from egg white and its properties have been characterized. The apoprotein-employing techniques for riboflavine detection in foods, urine, and blood serum are highly competitive with conventional labor-consuming procedures and with the high expensive HPLC method in sensitivity and selectivity, and can be recommended for riboflavine detection in biological objects.

[Serum levels of vitamin A, E, C and B2, carotenoid and zinc in hospitalized elderly patients]

Serum levels of carotenoids, zinc and vitamins A, E, C and B2 were measured in al (n = 202) the elderly patients hospitalized in different wards of the hospital studied from February 1986 to October 1988. The study was conducted on 130 men and 72 women with a mean age of 67.8 years (range: 60 to 88 years). The percentage of nutritional deficiency was 59.5% for zinc, 56.5% for vitamin C, 34.5% for vitamin B2, 25.9% for vitamin E, 13.2% for vitamin A, and 6.8% for carotenoids. Elderly patients with leucoses, megaesophagus, chronic obstructive pulmonary disease, and congestive heart failure represent a group with a high prevalence of deficiency both of zinc and of the vitamins under study. These results show the importance of detecting deficiencies of these micronutrients and provide a basis for a more rational approach to the treatment of elderly patients.

Assessment of vitamin B2 status in performance athletes of various types of sports

To determine the vitamin B2 supply, 62 athletes in various types of sports and 16 non-athletes were examined, using a weighed food record (7-day), alpha-EGR determination, microbiological blood, and HPLC urinary measurements. If the guidelines of 1.5 or 1.7 mg/day vitamin B2 or 0.6 mg/4,184 kJ (GRDA) are defined for adequate status, all sports groups (M +/- SEM) are above this level. The vitamin B2 blood concentrations show a range (mean) from 303-372 nmol/liter, which indicates that more than 90% of the athletes are above the reference value of 327 nmol/liter (mean). There is a correlation of r = 0.49 between the vitamin B2 intake (mean over 7 days) and the vitamin B2 blood level. Determination of vitamin B2 blood concentration is characterized by good precision (C.V. +/- 3.2%) and recovery (95.7%). The enzyme activation measurement (alpha-EGR) shows that all of the athletes are below the alpha-EGR reference value of < 1.50 (good supply). No significant correlations could be determined between alpha-EGR and vitamin B2 intake, blood concentrations, and urinary excretion. The measurement also shows high precision (C.V. 1.7%). The Vitamin B2 excretion in urine (mumol/g Cr.) was higher than the reference values for non-athletes in more than 90% of the athletes. There is a correlation of r = 0.89 between the vitamin B2 intake on the last day (Day 7) of the food record and the riboflavin excretion, and between vitamin B2 in blood and urinary excretion of r = 0.52. The C.V. of vitamin B2 urinary measurement using HPLC is 2.5%, with recovery of 98.2%. Combined measurement of vitamin B2 intake, blood concentration, and urine excretion appears to be a suitable procedure for determining the vitamin B2 status. Most of the performance athletes were sufficiently supplied with vitamin B2, compared to the reference values for non-athletes.

[Patients with type-II diabetes mellitus and neuropathy have no deficiency of vitamins A, E, beta-carotene, B1, B2, B6, B12 and folic acid]

The present study was aimed to determine the vitamin status of vitamins A, E, beta-carotene, B1, B2, B6, B12 and folate in plasma using HPLC and vitamins B1, B2 and B6 in erythrocytes using the apoenzyme stimulation test with the Cobas-Bio analyzer in 29 elderly type II diabetic women with (G1: n = 17, age: 68.6 +/- 3.2 years) and without (G2: n = 12, age: 71.8 +/- 2.7 years) diabetic polyneuropathy. The basic parameters as age, hemoglobin A1c, fructosamine and duration of the disease did not differ in both groups. Furthermore, retinopathy was assessed with fundoscopy and nephropathy with creatinine clearance. The creatinine clearance (G1: 50.6 +/- 3.4 vs. G2: 63.6 +/- 3.7 ml/min, 2p < 0.025) and the percentage of retinopathy (G1: 76.5% vs. G2: 16.7%, 2p = 0.002) were different indicating that G1 had significantly more severe late complications than G2. Current plasma levels of all measured vitamins (A, E, beta-carotene, B1, B2, B6, B12 and folate) and the status of B1, B2 and B6 in erythrocytes did not vary between the two groups (2p > 0.1). In summary, we found a lack of association between the actual vitamin condition in plasma and erythrocytes and diabetic neuropathy.

Direct assay of vitamins B1, B2, and B6 in hospitalized patients: relationship to level of intake

High-performance liquid chromatography assays for vitamins B1 by erythrocyte thiamine pyrophosphate, B2 by plasma and urinary riboflavin, and B6 by plasma pyridoxal phosphate and urinary pyridoxic acid were used to evaluate the B vitamin status of hospitalized patients. Over an intake range of up to 3.4 mg of thiamine per day and up to 4.1 mg of riboflavin per day, erythrocyte thiamine pyrophosphate and urine and plasma riboflavin increased proportionately with intake. There was no relationship between B6 intake and blood levels. Rather, a constant blood level was maintained with an intake range of 0.5 to 4 mg/d, and urinary pyridoxic acid showed a linear increase proportionate to intake. There were extremely variable blood and urine concentrations of B vitamins noted in our patient population.

Chemoprevention of oral leukoplakia and chronic esophagitis in an area of high incidence of oral and esophageal cancer

This intervention trial carried out in Uzbekistan (former USSR) in an area with a high incidence of oral and esophageal cancer involved random allocation of 532 men, 50 to 69 years old, with oral leukoplakia and/or chronic esophagitis to one of four arms in a double-blind, two-by-two factorial design, with active arms defined by the administration of (a) riboflavin; (b) a combination of retinol, beta-carotene, and vitamin E; or (c) both. Weekly doses were 100,000 IU of retinol, 80 mg of vitamin E, and 80 mg of riboflavin. The dose of beta-carotene was 40 mg/d. Men in the trial were followed for 20 months after randomization. The aim of the trial was to determine whether treatment with these vitamins or their combination could affect the prevalence of oral leukoplakia and/or protect against progression of oral leukoplakia and esophagitis, conditions considered to be precursors of cancer of the mouth and esophagus. A significant decrease in the prevalence odds ratio (OR) of oral leukoplakia was observed after 6 months of treatment in men receiving retinol, beta-carotene, and vitamin E (OR = 0.62; 95% confidence interval (CI): 0.39 to 0.98). After 20 months of treatment, no effect of vitamin supplementation was seen when the changes in chronic esophagitis were compared in the four different treatment groups, although the risk of progression of chronic esophagitis was lower in the subjects allocated to receive retinol, beta-carotene and vitamin E (OR = 0.65; 95% CI: 0.29 to 1.48) A secondary analysis not based on the randomized design revealed a decrease in the prevalence of oral leukoplakia in men with medium (OR = 0.45; 95% CI: 0.21 to 0.96) and high (OR = 0.59; 95% CI: 0.29 to 1.20) blood concentrations of beta-carotene after 20 months of treatment. Risk of progression of chronic esophagitis was also lower in men with a high blood concentration of beta-carotene, odds ratios being 0.30 (95% CI: 0.10 to 0.89) and 0.49 (95% CI: 0.15 to 1.58) for medium and high levels, respectively. A decrease in risk, also statistically not significant, was observed for high vitamin E levels (OR = 0.39; 95% CI: 0.14 to 1.10). These results were based on levels of vitamins in blood drawn after 20 months of treatment.

Periconceptional vitamin profiles are not suitable for identifying women at risk for neural tube defects

Folic acid and other vitamin deficiencies may play a role in the etiology of neural tube defects. The Medical Research Council Vitamin Study confirmed the beneficial effect of folic acid supplementation on the prevention of neural tube defects. However, the concentrations of vitamins other than folate were not a common feature of any of the former studies. We measured the concentrations of vitamin A, riboflavin, riboflavine-5'-monophosphate, flavine-adenine-dinucleotide, vitamin B-6, vitamin B-12, vitamin C, vitamin E, folate and ferritin in the serum of women who had previously had a child with a neural tube defect and were planning a further pregnancy. Vitamin and folic acid supplements were supplied before conception to 44 high risk women before conception. Eighteen other high risk women not given supplements were the control group. We concluded that vitamin profiles do not form a suitable means for identifying women at risk for neural tube defects before pregnancy. This endorses the hypothesis that the beneficial effect of folic acid supplementation on the prevention of neural tube defects is possibly at least partly due to the fact that it overrides a relative folic acid shortage caused by a metabolic disorder.

Erythrocyte vitamins B1, B2 and B6 and erythropoietin

The influence of recombinant human erythropoietin (r-HuEPO) on erythrocyte vitamins B1, B2 and B6 was investigated in regular dialysis treatment (RDT) patients during a long-term 9-month study. Twenty-six RDT patients were divided into two groups. Group A was without r-HuEPO treatment while group B was treated by subcutaneous injection of r-HuEPO. The total maintenance weekly dose of r-HuEPO was 50-100 U/kg. Group A of patients was supplemented with oral pyridoxine 5 mg/day during the period of 9 months; group B was supplemented with oral pyridoxine 5 mg/day for the first 6 months and with 20 mg/day during the following 3 months. At the end of the study, significant increase in erythrocyte vitamin B2 and significant decrease in erythrocyte vitamin B6 were found. Supplementation with 20 mg/day of pyridoxine led to a significant increase in vitamin B6 and at the end of the 9 months, the values of vitamin B6 were within the normal range. These results provide indirect evidence that erythrocyte vitamin B6 is consumed by the hemoglobin synthesis during r-HuEPO treatment in RDT patients.

[The provision of vitamins to school children in rural regions of Lithuania]

Providing with vitamins of schoolchildren was studied in some regions of Lithuania during the winter-spring period. The biochemical blood count has revealed insufficient providing of schoolchildren with ascorbic acid, beta-carotene, vitamins B1, B2 and B6. Decreased levels of ascorbic acid in urine, as well as micro-symptoms of hypovitaminosis (ascorbic acid, thiamine and riboflavine deficiencies) have been recorded.

[Riboflavin metabolism in diabetes mellitus]

Riboflavin excretion with urine in children suffering from diabetes mellitus is found to be significantly higher in comparison with healthy adults, the riboflavin content in the serum being normal. The total riboflavin concentration in erythrocytes is substantially lower and administration of daily-required riboflavin doses does not increase this parameter. FAD-dependent glutathione reductase in erythrocyte hemolysates is approximately 1.5 times higher than that of healthy children and does not depend on the additional intake of polyvitamins. The seeming affinity of the enzyme with exogenous FAD in sick children is almost 40 times lower in comparison with this value in healthy children, that is why the FAD-effect value in diabetes mellitus children does not exceed 1.2. Peculiarities of the riboflavin metabolism at diabetes mellitus and possibility to use the investigated parameters as criteria of vitamin B2 supply are discussed.

Low thyroxine levels in female psychiatric inpatients with riboflavin deficiency: implications for folate-dependent methylation

Intermediates in the folate-dependent methylation pathways may play a role in the etiology and treatment of such mental disorders as major depression. These pathways include a step dependent on a riboflavin (B2)-derived coenzyme, flavin adenine dinucleotide (FAD), which is reportedly sensitive to thyroid status and to phenothiazine and tricyclic drug exposure. In a sample of 52 male and female acute psychiatric inpatients, 17% (n = 9) showed B2 deficiency (i.e., insufficient FAD activity) on a functional red blood cell enzyme assay, but only one B2-deficient individual showed deficiency in another B-complex vitamin (folate). All patients with B2 deficiency were women, who were also significantly younger than the rest of the sample. The B2-deficient women had significantly lower thyroxine levels, even when controlling for sex and covarying for age. B2-deficient patients exhibited a nonsignificant trend toward more unipolar depression (44% vs 14%), but not toward bipolar or schizophrenic disorders. As in a previous study, drug exposure did not show a relationship to riboflavin deficiency in this sample. The findings suggest that B2 (FAD) activity may serve as a sensitive marker of thyroxine status in certain female psychiatric inpatients and that B2 deficiency may play an etiological role in defects of the methylation pathways in a subset of mentally ill individuals.

Thiamine, riboflavin, folate, and vitamin B12 status of low birth weight infants receiving parenteral and enteral nutrition

Thirty infants were randomly assigned to receive either 3 mL of MVI-Pediatric supplement (PAR3 group, parenterally fed) or 2 mL (PAR2 group, parenterally fed). For the first week, 100% received total parenteral nutrition (TPN), 50% by the second, and less than 33% by the third. Eighteen control infants received enteral feeds of infant formula. Baseline (before TPN) and subsequent weekly blood samples, dietary data, and 24-hour urine collections were obtained. The adequacies of thiamine and riboflavin were assessed by the thiamine pyrophosphate effect and erythrocyte glutathione reductase activity, respectively. Urinary thiamine and riboflavin levels were measured by fluorometry. Plasma folate, red blood cell folate, urinary folate, and plasma vitamin B12 concentrations were determined by radioassay. No differences between groups were observed in thiamine pyrophosphate effect, erythrocyte glutathione reductase activity, urinary B1 or B2, or red blood cell folate levels at any time. Plasma folate differed (p less than .05) among the PAR3 group (24 +/- 7 ng/mL), and both the PAR2 (13 +/- 5 ng/mL) and enterally fed (ENT) groups (16 +/- 3 ng/mL) before the initiation of feeds, at week 1 (PAR3 = 32 +/- 15 ng/mL; PAR2 = 18 +/- 4 ng/mL; ENT = 19 +/- 9, ng/mL) and between the PAR3 (30 +/- 16 ng/mL) and PAR2 (16 +/- 4 ng/mL) infants at week 2. Plasma vitamin B12 levels differed among the ENT groups (551 +/- 287 pg/mL) and both the parenteral groups (PAR2 = 841 +/- 405 pg/mL; PAR3 = 924 +/- 424 pg/mL) at week 1 and between the ENT (530 +/- 238 pg/mL) and PAR3 (999 +/- 425 pg/mL) groups at week 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Flavin levels in the rat retina

Exposure of riboflavin and its coenzymes adenine dinucleotide (FAD) and riboflavin-5'-phosphate (FMN) to UV and visible light results in the generation of radicals and photodegradative products that can damage surrounding macromolecules. Vertebrates and invertebrates have lost the ability to synthesize riboflavin and must obtain it or its coenzymes from food. The present study evaluated the relationship between FAD, FMN, and riboflavin concentrations in retina and blood of male Sprague-Dawley rats. Rations were provided in the form of purified diets containing 0, 3, 6, 30, and 300 mg riboflavin kg-1 diet. Analysis of flavins by HPLC showed that saturation levels of FAD, FMN and riboflavin in the retina and blood were achieved with diets containing 3 mg riboflavin kg-1. Retinal flavins were not significantly elevated by further increases in dietary riboflavin concentration, but an unidentified flavin appeared in the blood of rats given rations containing concentrations above 3 mg kg-1. The concentration of this unknown flavin varied in proportion to the level of dietary riboflavin.

Brief communication. Vitamin B1, B2, and B6 augmentation of tricyclic antidepressant treatment in geriatric depression with cognitive dysfunction

This was a 4-week randomized placebo-controlled double-blind study to assess augmentation of open tricyclic antidepressant treatment with 10 mg each of vitamins B1, B2, and B6 in 14 geriatric inpatients with depression. The active vitamin group demonstrated significantly better B2 and B6 status on enzyme activity coefficients and trends toward greater improvement in scores on ratings of depression and congnitive function, as well as in serum nortriptyline levels compared with placebo-treated subjects (Ss). Without specific supplementation, B12 levels increased in Ss receiving B1/B2/B6 and decreased in placebo Ss. These findings offer preliminary support for further investigation of B complex vitamin augmentation in the treatment of geriatric depression.

Blood levels and urinary excretion of thiamin and riboflavin during oral administration of multivitamin tablets to healthy adults

1. The baseline blood thiamin concentration increased gradually during the long-term administration of TTFD, and the blood concentration was dose-dependent. The cumulative urinary thiamin excretion showed the same dose-dependence as the blood concentration. 2. The baseline blood riboflavin concentration also increased steadily during the administration period, but the increase was less than that of thiamin. Dose-dependence of the cumulative urinary excretion of riboflavin was noted. 3. No side effect were observed.

Micronutrient status in females during a 24-week fitness-type exercise program

Thiamin, riboflavin, vitamin B6, magnesium, iron and zinc status, assessed from blood samples, was studied during a 24-week fitness-type exercise program. Subjects in exercise (n = 21) and control (n = 18) groups were female university students, aged 18-33 years. Erythrocyte (E) transketolase and glutathione activation coefficient, serum magnesium, zinc and ferritin, blood hemoglobin concentration and mean corpuscular volume were similar in both groups throughout the entire study. E-aspartate aminotransferase activation coefficient (vitamin B6 status) increased (4%) in exercise and decreased (7%) in control groups (p = 0.04), respectively. E-magnesium was stable in exercise but decreased (4%) in control groups (p = 0.004%). E-zinc increased (9%) in exercise subjects but remained stable in controls (p < 0.0001). A marginally altered vitamin B6 status was the only negative change found in exercise subjects.

[Comparison of biochemical criteria for supplying the human body with riboflavin]

Various biochemical procedures were used in evaluation of vitamin B2 occurrence in 38 women. Highly specific procedures for evaluation of riboflavin in blood and urine (high performance liquid chromatography, titration with riboflavin-binding apoprotein, lumiflavin procedure) enabled to detect correlation between values of FAD-effect and excretion of riboflavin with urine as well as of total riboflavin content in erythrocytes, between concentration of free riboflavin in blood plasma and its excretion with urine. All the procedures studied were equally suitable for evaluation of vitamin B2 deficiency as shown by the data obtained as well as by similarity in values of low concentrations which corresponded to normal availability of the vitamin.

Recurrent aphthous ulceration: vitamin B1, B2 and B6 status and response to replacement therapy

An evaluation of the thiamine, riboflavin and pyridoxine (vitamin B1, B2 and B6) status of 60 patients with recurrent mouth ulcers was performed. Seventeen patients (28.2%) were found to be deficient in one or more of these vitamins. Replacement therapy of these vitamins was given to a study group of deficient patients and a non-deficient group for one month. At the end of therapy and after a follow-up period of 3 months, only those patients who had a B complex deficiency had a significant sustained clinical improvement in their mouth ulcers. Vitamin B1, B2 and B6 deficiencies should, therefore, be considered as another possible precipitating factor in recurrent aphthous ulceration.

Multivitamin supplementation in oral contraceptive users

The effects of oral contraceptives (OC) containing 30 micrograms of ethinyl oestradiol and of subsequent multivitamin and folic acid supplementation on vitamin A, total B2 [including its three individual constituents, i.e. riboflavine, RB; flavine-mono-nucleotide, FMN; and flavine-adenine-dinucleotide, FAD], B12, C and folate concentration in serum and red blood cells have been studied in a group of 59 non-pregnant female volunteers. The group taking OC comprised 28 women while 31 women were included in the group of non-OC users serving as the controls. The women were studied for four cycles. Blood samples were taken on days 3 and 23 of the first cycle to obtain baseline values of each analyte. Multivitamin and folic acid supplementation started on day 1 of the second cycle and this was continued daily throughout three consecutive cycles until the end of the study. Vitamin A levels were significantly higher and vitamin B12 levels were significantly lower in the group using OC. Comparison of the baseline values of vitamin total B2, FAD, C, serum and red blood cell folate as determined on days 3 and 23 of the first cycle of the two groups compared revealed no significant differences. Multivitamin and folic acid supplementation did not affect the concentrations of vitamin A and vitamin B12 with either group, whereas all other vitamins increased significantly in both groups. The consistency of each effect of multivitamin supplementation between the two groups was also tested. The degree of these effects was not statistically different between both groups. The results suggest that the vitamin status is indeed affected by OC treatment, but the effects of multivitamin supplementation are not different in OC and non-OC users. Supplementation during OC use or just after discontinuing treatment cannot be justified for healthy young women. However, in the case of women with a critical vitamin balance or higher folate needs, multivitamin supplementation may be considered.

Intravenous vitamins for very-low-birth-weight infants

Term infants and children appear to adapt to large variations in vitamin intakes. This is supported by the finding of similar blood levels of vitamins despite several-fold differences in intake on a body weight basis. By contrast, the finding of marked elevation of some vitamins and low levels of others seen in very-low-birth-weight (VLBW) infants (less than 1500 g) suggest that this group has less adaptive capacity to high- or low-dose intakes. This indicates that their vitamin intakes need to be more closely aligned with actual needs. This paper reviews previously published data on vitamins A, E, B2, and B6 from VLBW infants receiving total parenteral nutrition (TPN). Vitamin A. VLBW infants are relatively deficient in retinol (R) at birth. During TPN large losses of R onto the delivery sets result in a further decline in stores of R as reflected in a progressive decline in plasma R during TPN. Because of the reported lower incidence of bronchopulmonary dysplasia associated with intramuscular vitamin A treatment, alternative methods of vitamin A delivery during TPN have been suggested. First, the vitamins were mixed with Intralipid (IL) and, second, retinyl palmitate (RP) rather than R was used. There was little in vitro loss of R when mixed with IL, and in vivo treatment resulted in higher blood levels after 1 month of retinol administration in IL than seen previously (21.4 +/- 4.2 vs 14.1 +/- 3.7 micrograms/dl).(ABSTRACT TRUNCATED AT 250 WORDS)

[A comparison of fluorescent methods of determining the concentration of vitamin B2 in blood]

Three methods of riboflavin assay in the human blood were comparatively studied. It has been found that firmly-bound flavin forms present in erythrocytes inhibit their complete transmission into the riboflavin form. Low specificity of the method using riboflavin fluorescence suppression with dithionite has been proved. Dithionite capacity for suppressing fluorescence of riboflavin-like substances significantly rises detectable levels. The use of riboflavin-binding protein permits one to determine only free riboflavin form. It has been established that the lumiflavin method is most reliable and specific for riboflavin assay in erythrocytes.