A Simplified Sample Preparation Method for the Assessment of Plasma Ascorbic Acid in Clinical Settings.

BACKGROUND: Vitamin C deficiency is difficult to diagnose on the basis of clinical presentation alone and requires plasma levels for confirmation. Reference laboratories typically specify shipment of plasma on dry ice. This requirement may complicate clinic work flow and delay vitamin C measurement. Additionally, patients with vitamin C deficiency may experience unnecessary testing and increased health-care costs, as other diagnoses are often considered first. We examined an alternative, more practical shipping method. METHODS: Plasma was collected from 17 healthy volunteers by use of heparin tubes with gel separators, and all tubes were centrifuged immediately to separate the plasma layer from the cells. Baseline vitamin C was measured in plasma obtained immediately after specimen collection. Remaining sample tubes were held in Styrofoam containers with cold packs for 30 h or 48 h, followed by vitamin C measurement. Additional samples were exposed to conditions that simulated harsher shipping conditions. RESULTS: Mean plasma vitamin C was 69.6 µmol/L (SD = 21.5 µmol/L). Vitamin C losses were 5.4% at 30 h (SD = 5.55%, P < 0.05) and 7.6% at 48 h (SD = 5.56%, P < 0.05), which is slightly more than freeze-and-thaw treatment (average loss of 1.4%, SD = 6.9%, NS). The vitamin C method had an intraday variation of 1.88%. Vigorous shaking of 2 samples for 24 h resulted in a -1.9% change in 1 sample, and a +4.1% change in another sample. Exposure of the shipping container to elevated temperature (35 °C for 30 h) did not change the internal temperature of the container. CONCLUSIONS: The shipping procedure uses routine sample handling, standard vacutainers, and can be replicated by health-care centers seeking to evaluate patient vitamin C status.

Plasma oxalate levels in prevalent hemodialysis patients and potential implications for ascorbic acid supplementation.

OBJECTIVES: Ascorbic acid (AA) supplementation may increase hemoglobin levels and decrease erythropoiesis-stimulating agent dose requirement in patients with end stage renal disease (ESRD). While plasma AA levels >100µM may be supratherapeutic, levels of at least 30µM may be needed to improve wound healing and levels may need to reach 70µM to optimize erythropoiesis. Of concern, oxalate (Ox), an AA metabolite, can accumulate in ESRD. Historically, if plasma Ox levels remain ≥30µM, oxalosis was of concern. Contemporary hemodialysis (HD) efficiencies may decrease the risk of oxalosis by maintaining pre-HD Ox levels <30µM. This study focuses on the plasma Ox levels in HD patients. DESIGN AND METHODS: A prospective, observational study of 197 HD patients with pre-HD AA levels and pre-HD and post-HD Ox levels. RESULTS: Mean plasma Ox levels decreased 71% during the intradialytic period (22.3±11.1µM to 6.4±3.2µM, P<0.001). In regression analysis, pre-HD plasma AA levels ≤100µM were not associated with a pre-HD plasma Ox level≥30µM, even if ferritin levels were increased. Pre-HD plasma Ox levels ≥20 or ≥30µM were not associated with lower cumulative 4-year survival. CONCLUSIONS: Pre-HD plasma AA levels up to 100µM in HD patients do not appear to be associated with an increased risk of developing secondary oxalosis, as the corresponding pre-HD plasma Ox level appears to be maintained at tolerable levels.

Plasma ascorbic acid concentrations in prevalent patients with end-stage renal disease on hemodialysis.

OBJECTIVE: To determine the prevalence of vitamin C (ascorbic acid [AA]) deficiency in patients with end-stage renal disease, the effect of supplemental AA on plasma AA concentrations, and the extrinsic and intrinsic factors that affect plasma AA concentrations in this patient population. DESIGN: In study 1, we compared the effect of hemodialysis (HD) on plasma AA concentrations between patients with low and high pre-HD AA concentrations. In study 2, we analyzed kinetic and nonkinetic factors for their association with increased plasma AA concentrations in patients on maintenance HD. Study 1 was performed in a single outpatient HD clinic in Cherry Hill, New Jersey. Study 2 was performed in 4 outpatient HD clinics in Southern New Jersey. SUBJECTS AND INTERVENTION: In study 1, we collected plasma samples from 8 adult patients on maintenance HD at various time points around their HD treatment and assayed them for AA concentration. In study 2, we enrolled 203 adult patients and measured pre-HD plasma AA concentrations. We ascertained supplemental AA use and assessed dietary AA intake. MAIN OUTCOME MEASURE: In study 1, plasma AA concentrations were compared during the intradialytic and interdialytic period. In study 2, pre-HD plasma AA concentrations were correlated with supplement use and demographic factors. RESULTS: Study 1 showed that over the course of a single HD treatment, the plasma AA concentration decreased by a mean (±standard deviation) of 60% (±6.6). In study 2, the median pre-HD plasma AA concentration was 15.7 µM (interquartile range, 8.7-66.8) in patients who did not take a supplement and 50.6 µM (interquartile range, 25.1-88.8) in patients who did take a supplement (P < .001). Supplement use, increasing age, and diabetes mellitus were associated with a pre-HD plasma AA concentration ≥30 µM. CONCLUSION: HD depletes plasma AA concentrations, and AA supplementation allows patients to achieve higher plasma AA concentrations.

Is vitamin C intake too low in dialysis patients?

Vitamin C has several well-established roles in physiology including synthesis of collagen, carnitine and epinephrine, absorption of dietary iron, and mobilization of storage iron for erythropoeisis. Loss of several of these functions explains the pathology of scurvy, where defective collagen synthesis and anemia are major symptoms. Vitamin C deficiency is very common in dialysis patients and may arise from dialytic vitamin C clearance, restricted intake of vitamin C-rich foods, and increased vitamin C catabolism in vivo from inflammation. In the dialysis population, greater vitamin C intake may be needed for optimal health. Relationships between intake, body distribution, inflammation, and dialytic losses are complex and need further study. Concern about vitamin C metabolism leading to accumulation of tissue oxalate has led to the recommendation that vitamin C intake equals, but not exceeds, the intake recommended for the general population. Vitamin C deficiency in dialysis patients may have clinical consequences; a study in Renal Research Institute clinics found an association with periodontal disease. Data also support a role for vitamin C in prevention of dialysis-related anemia. New research questions are proposed in this editorial, with a discussion of strategies to determine the optimal provision of vitamin C for CKD patients.

Beneficial hematologic effects of daily oral ascorbic acid therapy in ESRD patients with anemia and abnormal iron homeostasis: a preliminary study.

AIM: To determine the efficacy and effects of the oral administration of ascorbic acid on anemia management in ESRD patients with hyperferritinemia. METHODS: Twenty-one anemic hemodialysis patients with ferritin levels greater than 350 ng/mL had received oral daily ascorbic acid at a dose of 500 mg/day and were retrospectively studied. Hemoglobin, hematocrit, EPO dose, ferritin, and transferrin saturation were recorded at baseline and after three months of treatment. EPO dose/hematocrit was calculated. Serum oxalate levels were also measured. RESULTS: Hb increased 9% from 11.4 to 12.2 gm/dL (p = 0.05), HCT increased 10% from 33.3 to 36.7% (p = 0.05), but EPO dose requirement decreased 33% from 26,229 to 17,559 U/week (p = 0.03). Ferritin levels decreased 21% from 873 to 691 ng/mL (p = 0.004). Mean oxalate level during therapy was 87 micromol/L (normal <27). Patients with oxalate levels >27 micromol/L were instructed to stop ascorbic acid treatment, and mean levels decreased from 107 to 19 micromol/L (p = 0.01) over a mean time of 71 days. CONCLUSION: In this study, daily oral ascorbic therapy decreased ferritin levels and EPO dose requirements while raising hemoglobin and hematocrit level. This beneficial profile of effects of ascorbic acid therapy is consistent with improvement of EPO resistance and cost savings in this population.