Notice of correction for Johnson et al. : A Randomised Study of Allopurinol on Endothelial Function and eGFR in Asymptomatic Hyperuricemic Subjects with Normal Renal Function. August 2011 (8) 1887–1894 doi: 10.2215/CJN.10801011 The authors have noted incorrect statistical analysis performed in Table 2 and Figure 3 of this paper.
Table 2.
The mean serum uric acid (UA), flow mediated dilatation (FMD), mean systolic (SBP) and diastolic (DBP) blood pressure at baseline and 16 wk after
| Allopurinol group (n = 30) |
Hyperuricemic control group (n = 37) |
Normouricemic control group (n = 30) |
|||||||
|---|---|---|---|---|---|---|---|---|---|
| Baseline | 16 wks | P | Baseline | 16 wks | P | Baseline | 16 wks | P | |
| Uric acid (mg/dl) | 8.3 ± 1.1 | 5.9 ± 1.5 | < 0.001 | 7.9 ± 0.7 | 7.2 ± 0.83 | 0.0009 | 4.4 ± 1.0 | 4.5 ± 0.86 | 0.28 |
| Flow-mediated dilatation (%) | 7.74 ± 0.93 | 8.12 ± 1.55 | 0.03 | 7.77 ± 0.86 | 7.76 ± 0.85 | 0.99 | 9.16 ± 0.66 | 9.24 ± 0.66 | 0.19 |
| eGFR (ml/min/1.73 m2) | 86.3 ± 19.4 | 89.6 ± 12.7 | 0.002 | 84.3 ± 16.7 | 84.4 ± 16.3 | 0.30 | 92.9 ± 13.8 | 93.3 ± 9.3 | 0.94 |
| hsCRP (mg/dl) | 7.4 ± 5.8 | 4.6 ± 3.7 | 0.006 | 6.9 ± 3.4 | 5.9 ± 3.8 | 0.03 | 3.3 ± 2.5 | 3.5 ± 2.2 | 0.85 |
| Mean SBP (mmHg) | 127.6 ± 14.4 | 116.9 ± 11.7 | 0.003 | 123.2 ± 13.5 | 116.8 ± 10.0 | 0.007 | 119.4 ± 11.2 | 116.4 ± 12.4 | 0.21 |
| Mean DBP (mmHg) | 75.1 ± 7.8 | 74.9 ± 12.4 | 0.93 | 75.6 ± 8.7 | 73.9 ± 12.5 | 0.45 | 77.4 ± 6.1 | 76.3 ± 11.8 | 0.66 |
Δ uric acid was different between the Allopurinol group and Normouricemic control group and between Hyperuricemic control group versus Normouricemic control group after adjusting for baseline.
Figure 3.
Figure has also been redrawn based on the reanalysis. The figure depicts FMD values (box-whisker plots with median values with significant differences were noted by rank tests) at baseline and at the 4th month evaluation in hyperuricemic, allopurinol and normouricemic groups. Similar to the original analysis, only the allopurinol group shows a significant change in FMD when pre- and postintervention values are compared.
The authors had the data reanalyzed by Dr Kim McFann from the Biostatistics Department at the University of Colorado. The major conclusions, which were that allopurinol can improve eGFR and flow mediated dilation, were confirmed.
The original statistical analysis used a one way ANOVA with paired t tests, but had numerous errors in rounding and analyses. Re-analysis was performed using the one-way ANOVA followed by a Tukey-Kramer p-value adjustment to compare continuous variables between groups post hoc for those significant in the omnibus test as well as the Kruskall-Wallis Test. Change between baseline and 16 wk within groups was tested using a paired Wilcoxon sign rank test due to the non-normality of the change. FMD before and after treatment was regressed on uric acid, age, gender, CRP, GFR and SBP in multivariate linear regression. A P < 0.05 for the final model was considered as statistically significant. Data were analyzed using SAS 9.2 for Windows software (SAS® Cary, NC). The primary findings are shown below in the corrected Table 2.
The primary findings that allopurinol improved eGFR, FMD, systolic BP and hs-CRP were confirmed with the reanalysis. However, the re-analysis also showed that the hyperuricemic control group had a lesser, but still significant fall in serum uric acid, and this was associated with a significant fall in systolic BP and hs-CRP level. In contrast, no changes in any parameters were noted in the normouricemic group.
The observation that the hyperuricemic control group had a reduction in uric acid could be due to change in dietary habits related to awareness that they had high uric acid values. Nevertheless, the observation of parallel changes in uric acid with systolic BP and hs-CRP would be consistent with an effect of uric acid on these parameters. The authors report there were errors in the original statistical analysis. However, the re-analysis does confirm that lowering uric acid may have significant benefits on endothelial and renal function in subjects with asymptomatic hyperuricemia.