In the recent study “Mortality in Patients with IgA Nephropathy” published in AJKD, Knoop et al describe the clinical outcomes of patients diagnosed with IgA nephropathy (IgAN) on kidney biopsy in Norway. Although the excess mortality with chronic kidney disease (CKD) compared with the general population is well described, mortality data specific to IgAN are lacking. Whereas most CKD patients have a higher risk of death than of developing end stage renal disease (ESRD), it is unknown if this pattern applies to patients with IgAN.
Knoop et al performed a cohort study of 633 patients with IgAN identified through the Norwegian Kidney Biopsy Registry between 1988 and 2004. To identify which of these patients had died or reached ESRD, the authors used the Norwegian Cause of Death Registry and Norwegian Renal Registry, respectively. Patients with IgAN were divided into low, moderate, and high risk subsets based on estimated GFR (eGFR), proteinuria, and the Japanese scoring system for IgA nephropathy severity. The mortality rate of IgAN was analyzed using standardized mortality ratio (SMR) to compare the observed versus expected death rate for age and gender-matched Norwegians.
The mean followup duration for 633 patients with IgAN was 11.8 years. 146 patients developed ESRD, with most of these undergoing kidney transplantation. Not surprisingly, the higher risk cohorts by any of the three above criteria had substantially higher rates of progressing to ESRD during the follow-up time. Few of the patients in the low risk groups (eGFR >60 mL/min/1.73m2, proteinuria <1g/24 h, or the low risk Japanese predictive model) progressed to ESRD, whereas the majority of those with high risk characteristics did.
Only 45 of the 487 patients who did not develop ESRD died, a much lower proportion than the 35 of 146 with ESRD. Of these, a much higher percentage of the ESRD deaths occurred in patients managed with dialysis. Overall, the SMR of the entire cohort with IgAN was higher than the general population in Norway, although this did not apply to the low risk groups who had equivalent SMR to age and gender-matched patients in the general population. When SMR was determined in the pre-ESRD period, there was no difference. However, the SMR was significantly higher in patients with ESRD, a finding more pronounced with dialysis but also observed with transplant recipients.
The important finding of this study is that mortality rates are higher in Norwegian patients with IgAN when compared to the overall population, but that this is limited to the higher risk subgroups who had the greatest likelihood of progressing to ESRD. The higher mortality was driven by the development of ESRD as the highest proportion of deaths occurred after dialysis or to a lesser degree transplantation. Importantly, the low risk groups with IgAN not only had lower rates of progressing to ESRD, but also had mortality rates similar to the general population.
Craig Gordon, MD, MS