Six RCTs (n=326, range 18 to 153) were included in the review: four parallel and two cross-over designs. The quality of the RCTs was generally poor; two reported the randomisation process and only one of these reported allocation concealment. Only one RCT reported blinding. All trials used intention-to-treat analysis. Loss to follow-up ranged between 0% and 28%.
There were statistically significant improvements in patients who received ascorbic acid compared to controls for haemoglobin concentration (WMD 0.9g/dL, 95% CI 0.5 to 1.2; three RCTs, n=125) and transferrin saturation (WMD 7.9%, 95% CI 5.2 to 10.5; five RCTs, n=173). rHuEPO dose was statistically significantly reduced in patients who received ascorbic compared with controls (WMD -17.1 U/kg/wk, 95% CI -26.0 to -8.2; five RCTs, n=303). There was no statistically significant difference in ferritin concentration between patients who received ascorbic acid or control (five RCTs, n=266). There was no evidence of significant statistical heterogeneity for any comparisons. Sensitivity analysis did not alter the results significantly.
Adverse events were poorly reported in the included trials and had questionable relevance to the use of ascorbic acid. Details were reported in the review.
There was no evidence of publication bias using Begg’s and Egger’s tests.