A new enzymatic method for pyridoxal‐5‐phosphate determination

Shin-Buehring, Y.S.; Raßhofer, R.; Endres, W.

doi:10.1007/bf02263621

Cited by 72 publications

(37 citation statements)

References 3 publications

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“…The mean betweenlaboratory recovery improved to 97.6% when the amount of PLP added was increased to 62.4 nmol/L. These recoveries seem to be consistent with the literature; a selection of published methods for PLP suggest that analyte addition recoveries of 88%-103% (betweenmethod mean of 95%) are typical for HPLC methods (2, 7, 9 -13, 25 ) and recoveries of 83%-125% (betweenmethod mean of 99%) can be expected from enzymatic methods (3)(4)(5). Because the recovery calculation was based on a gravimetrically determined amount of PLP and the actual amount of the PLP addition was not measured in each laboratory, actual recoveries in each laboratory may vary slightly depending on calibration accuracy.…”

Section: Discussionsupporting

confidence: 86%

“…Cases were also observed in which the mean within-day CV for a laboratory apparently exceeded its mean between-day CV; these likely were artifacts arising from the relatively small number of pools used to assess within-day imprecision (n ϭ 3) compared with between-day imprecision (n ϭ 20). In comparison, data from several published methods for measuring PLP in human plasma or serum suggest that within-and between-day CVs are typically 0.5%-5.9% and 3.6%-11.8%, respectively, for HPLC methods (2, 7-9, 13, 14 ) and 3.0%-11% and 7.9%-13%, respectively, for enzymatic methods (3)(4)(5). It should be noted, however, that the number of within-or between-day measurements used for determining CVs in these studies was considerably greater (typically 10 -20 per specimen in each case) than the number of measurements used in the present study.…”

Section: Discussionmentioning

confidence: 99%

“…Clinical vitamin B 6 analysis is accomplished at present by a variety of enzymatic assays (3)(4)(5)(6) and HPLC methods (7)(8)(9)(10)(11)(12)(13)(14). Although some direct comparisons of these methods can be found in the literature (usually in the form of comparing results from a new method with an established one as a part of method validation), objective comparative studies of vitamin B 6 measurements among several methods or laboratories are rare.…”

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confidence: 99%

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Clinical Vitamin B6 Analysis: An Interlaboratory Comparison of Pyridoxal 5′-Phosphate Measurements in Serum

Rybak¹,

Jain²,

Pfeiffer³

2005

Clinical Chemistry

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Background: Recent investigations into the role vitamin B 6 plays in reducing risk of stroke and cardiovascular disease have heightened interest in vitamin B 6 intake and its relationship to clinical status indicators. Because a true reference method and certified reference materials are lacking, little is known about the relative analytical performance of clinical vitamin B 6 assays. Methods: Ten laboratories experienced in clinical vitamin B 6 analysis participated in a 3-day analysis of 69 serum and 3 aqueous specimens for pyridoxal 5-phosphate (PLP). Laboratories used either HPLC-based or enzymatic assays. Results were analyzed for imprecision, recovery, and bias relative to consensus means. Results: Among laboratories, mean within-day CVs (3 specimens ؋ 3 measurements/day) were 0.6%-37% and between-day CVs (20 specimens ؋ 1 measurement/ day ؋ 3 days) were 1.4%-26%. Mean recoveries of added PLP were 53%-144%, and mean sample pool mixing recoveries were 75%-119%. Consensus means calculated for 20 serum specimens gave mean relative biases between measurement of ؊10.0% to 24.3% among participating laboratories over a range of 15.8 -319 nmol/L PLP. Measurement imprecision and biases were evaluated against empirically derived performance criteria based on biological variation. Three of 10 laboratories met optimum imprecision requirements and had 90% or more of measurements satisfy optimum criteria for biases among methods. All 10 laboratories met minimum imprecision requirements, but 25%-53% of the results reported by 4 of the 7 suboptimal laboratories failed to satisfy the minimum criteria for bias.

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Section: Discussionsupporting

confidence: 86%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Clinical Vitamin B6 Analysis: An Interlaboratory Comparison of Pyridoxal 5′-Phosphate Measurements in Serum

Rybak¹,

Jain²,

Pfeiffer³

2005

Clinical Chemistry

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“…Antithrombin, protein C, protein S, factor VIII activity, lupus anticoagulant, factor V Leiden and prothrombin G20210A were determined by routine methods. Plasma PLP was measured by the tyrosine decarboxylase method, 11 and plasma total homocysteine (tHcy) by high performance liquid chromatography (Waters, USA), using a commercially available assay (Immundiagnostik, Germany).…”

Section: Blood Sampling and Laboratory Analysismentioning

confidence: 99%

Low vitamin B6 levels and the risk of recurrent venous thromboembolism

Hron¹,

Lombardi²,

Eichinger³

et al. 2007

Haematologica

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Low plasma vitamin B6, measured as pyridoxal-5'-phosphate (PLP), is associated with an increased risk of first venous thromboembolism (VTE). In a prospective cohort of 757 patients with first VTE we investigated the association of PLP levels with risk of recurrent VTE. After 4 years, the likelihood of VTE recurrence was 22.5% (95% CI 13.6-31.5%) among patients with PLP ≤23.3 nmol/L and 14.4% (11.5-17.4%) among those with PLP >23.3 nmol/L (p=0.01). Patients with PLP ≤23.3 nmol/L had 1.8-fold higher recurrence risk (1.01-3.14) than patients with PLP >23.3 nmol/L (adjusted for confounders including homocysteine). Therefore, low vitamin B6 is a risk factor of recurrent VTE. ABSTRACTT he association between severe hyperhomocysteinemia and recurrent venous thromboembolism (VTE) is well established, and treatment of these patients with homocysteine-lowering vitamins decreases the incidence of recurrent events.

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“…tHcy levels were determined by high-performance liquid chromatography with fluorescence detection (25). Plasma pyridoxal 5Ј-phosphate (PLP) (the active form of B6) levels were measured by radioenzymatic (tyrosine decarboxylase) assay (26), and plasma folate and B12 levels were ascertained by radioassay (Bio-Rad Quantaphase II; Bio-Rad, Hercules, CA). Serum albumin, creatinine, HbA 1c , lipid levels, and 24-h urinary protein levels were measured using standard automated clinical chemistry techniques.…”

Section: Study Patientsmentioning

confidence: 99%

Proteinuria as a Predictor of Total Plasma Homocysteine Levels in Type 2 Diabetic Nephropathy

Friedman

Hunsicker²,

Selhub³

et al. 2002

Diabetes Care

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OBJECTIVE -Patients with diabetes who manifest proteinuria are at increased risk for cardiovascular events. Some studies suggest that proteinuria exerts its cardiovascular effects at least partly through a positive association with total plasma homocysteine (tHcy). Modestly sized but better designed contrary studies find no such link through a limited range of serum creatinine and proteinuria. We tested the hypothesis that proteinuria independently predicts tHcy levels in a larger cohort of type 2 diabetic patients with nephropathy throughout a much broader range of kidney disease and proteinuria.RESEARCH DESIGN AND METHODS -Baseline data for the cross-sectional study were obtained from 717 patients enrolled in the multicenter Irbesartan Diabetic Nephropathy Trial. All subjects had type 2 diabetes, hypertension, and proteinuria and were between 29 and 78 years of age. Data included age, sex, BMI, serum creatinine and albumin, LDL and HDL cholesterol, triglyceride, proteinuria and albuminuria, plasma folate, B12, and pyridoxal 5Ј-phosphate (PLP) (the active form of B6), HbA 1c , and tHcy levels. Unadjusted and multivariable models were used in the analysis.RESULTS -Crude analyses revealed significant associations between tHcy and age (r ϭ 0.074; P ϭ 0.008), creatinine (r ϭ 0.414; P Ͻ 0.001), PLP (r ϭ Ϫ0.105; P ϭ 0.021), B12 (r ϭ Ϫ0.216; P Ͻ 0.001), folate (r ϭ Ϫ0.241; P Ͻ 0.001), and HbA 1c (r ϭ Ϫ0.119; P ϭ 0.003), with serum albumin approaching significance (r ϭ 0.055; P ϭ 0.072). Only serum creatinine, plasma folate, B12, serum albumin, sex, HbA 1c , and age were independent predictors of tHcy after controlling for all other variables.CONCLUSIONS -By finding no independent correlation between proteinuria (or albuminuria) and tHcy levels, this study improves the external validity of previous negative findings. Therefore, it is unlikely that the observed positive association between proteinuria and cardiovascular disease is directly related to hyperhomocysteinemia.

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A new enzymatic method for pyridoxal‐5‐phosphate determination

Cited by 72 publications

References 3 publications

Clinical Vitamin B6 Analysis: An Interlaboratory Comparison of Pyridoxal 5′-Phosphate Measurements in Serum

Clinical Vitamin B6 Analysis: An Interlaboratory Comparison of Pyridoxal 5′-Phosphate Measurements in Serum

Low vitamin B6 levels and the risk of recurrent venous thromboembolism

Proteinuria as a Predictor of Total Plasma Homocysteine Levels in Type 2 Diabetic Nephropathy

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