Association between glomerular filtration rate (measured by high-performance liquid chromatography with iohexol) and plasma oxalate / Associação entre taxa de filtração glomerular (medida por cromatografia liquida de alto desempenho com iohexol) e oxalato plasmático

ABSTRACT Introduction: Secondary hyperoxalemia is a multifactorial disease that affects several organs and tissues in patients with native or transplanted kidneys. Plasma oxalate may increase during renal failure because it is cleared from the body by the kidneys. However, there is scarce evidence about the association between glomerular filtration rate and plasma oxalate, especially in the early stages of chronic kidney disease (CKD). Methods: A case series focuses on the description of variations in clinical presentation. A pilot study was conducted using a cross-sectional analysis with 72 subjects. The glomerular filtration rate (GFR) and plasma oxalate levels were measured for all patients. Results: Median (IQR) GFR was 70.50 [39.0; 91.0] mL/min/1.73 m2. Plasma oxalate was < 5.0 µmol/L in all patients with a GFR > 30 mL/min/1.73m2. Among the 14 patients with severe CKD (GFR < 30 mL/min/1.73 m2) only 4 patients showed a slightly increased plasma oxalate level (between 6 and 12 µmol/L). Conclusion: In non-primary hyperoxaluria, plasma oxalate concentration increases when GFR < 30mL/min/1.73 m2 and, in our opinion, values greater than 5 µmol/L with a GFR > 30 mL/min/1.73 m2 are suggestive of primary hyperoxaluria. Further studies are necessary to confirm plasma oxalate increase in patients with low GFR levels (< 30mL/min/1.73 m2).

RESUMO Introdução: A hiperoxalemia secundária é uma doença multifatorial que afeta vários órgãos e tecidos em pacientes com rins nativos ou transplantados. O oxalato plasmático pode aumentar durante a insuficiência renal porque é eliminado do corpo pelos rins. No entanto, há evidências escassas sobre a associação entre taxa de filtração glomerular e oxalato plasmático, especialmente nos estágios iniciais da doença renal crônica (DRC). Métodos: uma casuística centrada na descrição das variações na apresentação clínica. Foi realizado um estudo piloto a partir da análise transversal com 72 indivíduos. As taxas de filtração glomerular (TFG) e os níveis plasmáticos de oxalato foram medidos para todos os pacientes. Resultados: A TFG mediana (IIQ) foi de 70,50 [39,0; 91,0] mL/min/1,73 m2. O nível plasmático de oxalato foi < 5,0 µmol/L em todos os pacientes com TFG > 30 mL/min/1,73 m2. Entre os 14 pacientes com DRC grave (TFG < 30 mL/min/1,73 m2), apenas quatro apresentaram ligeiro aumento do nível plasmático de oxalato (entre 6 e 12 µmol/L). Conclusão: Na hiperoxalúria não primária, a concentração plasmática de oxalato aumenta quando TFG < 30 mL/min/1,73 m2 e, em nossa opinião, valores superiores a 5 µmol/L com TFG > 30 mL/min/1,73 m2 sugerem presença de hiperoxalúria primária. Estudos adicionais são necessários para confirmar o aumento do oxalato plasmático em pacientes com níveis baixos de TFG (< 30 mL/min/1,73 m2).

Urinary & serum oxalate determination by oxalate oxidase immobilized on to affixed arylamine glass beads.

BACKGROUND & OBJECTIVE: Although the measurement of oxalate in urine and serum by Amaranthus leaf oxalate oxidase immobilized on free arylamine glass beads is highly sensitive and specific, the handling of glass beads is tedious and cumbersome. The present study was undertaken to overcome this problem. METHODS: Partially purified Amaranthus spinosus leaf oxalate oxidase was immobilized through diazotization onto arylamine glass beads affixed on the surface of a plastic strip by a non reactive fixative and employed for oxalate determination in urine and serum samples collected from healthy individuals and urinary stone formers. RESULTS: The immobilized enzyme retained 56 per cent of its initial activity with a conjugation yield of 40 mg/g support. The strip bound enzyme showed maximum activity at pH 3.5 when incubated at 40 degrees C for 15 min. The minimum detection limit of the method was 0.01 mM/l in the urine and 2.5 microM/l in the serum. The analytical recovery of added oxalate was 97.7+/-1.2 per cent in urine and 92.0+/-2.4 per cent in serum. Within and between assay coefficient of variation (CV) were 4.6 and 5.2 per cent in urine and 7.4 and 5.8 per cent in serum respectively. A good correlation for oxalate in urine (r1= 0.99) and in serum (r2= 0.92) was obtained between Sigma kit method and the present method. The strip could be reused 150 times over a period of 2 months, when stored at 4 degrees C in reaction buffer. INTERPRETATION & CONCLUSION: Immobilization of Amaranthus leaf oxalate oxidase on to affixed glass beads provided enormous ease in its reuse for determination of oxalate in urinary and serum samples.

Efficacy and safety of oral versus intravenous vitamin C in hemodialysis patients with functional iron deficiency

Hemodialysis patients [HD] with functional iron deficiency[FID] often develop resistance to recombinant human erythropoietin [rHuEpo]. Recent studies suggest that intravenous ascorbic acid [IVAA] may circumvent rHuEpo resistance, while oral [AA] is readily attainable. The aim of this study was to evaluate efficacy and safety of oral versus intravenous vitamin C on FID and whether this can improve anemia in hemodialysis patients. In this study, 31 hemodialysis patients with serum ferritin >100 micro g/L, transferin saturation [TS] < 30% and Hb <11g/dL were selected and randomly divided into the oral and IV groups. The IVAA group received vitamin C 1.5 g, administered weekly and the oral group, 125 mg vitamin C daily for two months. Hb, ferritin, serum iron, Tsat and serum oxalate were measured at the beginning of the study and 2 months later. Independent - sample T-Test were used for intergroup comparison. P value < 0/05 was considered significant. Mean Hb difference was 1.1 +/- 0.7g/dL in the oral and 0.1 +/- 1g/dL in the IVAA group, being significantly higher in the oral group [p=0.02]. There were no significant differences between the two groups in the delta means of ferritin and Tsat [p=0.5, p=0.3]. Delta means of serum oxalate in the 2 groups were 0.05 +/- 0.4mg/L, and 0.1 +/- 0.3mg/L respectively, difference not significant [p=0.3]. Oral AA significantly increased Hb in HD patients suffering from FID. Considering the feasibility and cost-effectiveness, clinicians could consider oral instead IVAA in rHuEpo hyporesponsive patients undergoing HD

Determination of plasma oxalate with chloride ion insensitive oxalate oxidase.

A simple colorimetric method has been developed for determination of oxalate in plasma using a C1-insensitive oxalate oxidase purified from grain sorghum leaves. The ultrafiltered plasma collected in 3.5 N HC1 was pretreated with NaNO2 to avoid possible interference by ascorbate. The minimum detection limit of the method is 0.225 mg/l. The % recovery of the added oxalate was 91.5 +/- 5.0 (mean +/- S.D., n = 15). The coefficient of variation within and between batch were < 3 and < 5 respectively. The mean plasma oxalate concentration in healthy subjects was 0.29 mg/l. The method has the advantage over other enzymic methods that it doesn't require the removal of C1- prior to oxalate assay.