IgA Deficiency & Mortality: A Population-Based Cohort Study

Abstract

IgA deficiency has been linked to increased mor- bidity but data on mortality is lacking. In this population- based prospective cohort study we examined mortality in patients with IgA deficiency compared with the general population. Through six university hospitals in Sweden we identified 2,495 individuals with IgA deficiency (IgA deficiency≤0.07 mg/L) diagnosed between 1980 and 2012. Each patient with IgA deficiency was matched on age, sex, place of residence, and year of diagnosis with up to 10 general population controls (n=24,509). Data on education level and emigration status were obtained from Statistics Sweden. Our main outcome measure was all-cause mortality retrieved from the nationwide Causes of Death Register, which includes >99 % of all deaths in Sweden. We used Cox regression to estimate mortality hazard ratios condi- tioned on the matching factors and adjusted for education level. During 25,367 person-years of follow-up (median 8.3), there were 260 deaths in the IgA deficiency group versus 1, 599 deaths during 257,219 person-years (median 8.6) in the general population controls (102 versus 62 deaths per 10,000 person-years; incidence rate difference, 40, 95%CI 28-53, P <.001). This corresponded to a conditional mortality hazard ratio of 1.8 (95%CI 1.6-2.1, P<.001). Relative mortal- ity varied by follow-up time (P<.001) from a hazard ratio of 3.6 (95%CI 2.5-5.3; P<.001) during the first year to 1.9 (95%CI 1.5-2.4; P<.001) year 1-4; 1.9 (95%CI 1.4-2.4; P<.001) year 5-9; 1.5 (1.0-2.2; P=.054) year 10-14.9; and 1.1 (0.7-1.6; P =.66) year 15-25. Effect modification was also seen by age in each stratum of follow-up time, with higher relative mortality in younger than older patients (P<.001). In conclusion, patients with IgA deficiency are at increased risk of death in the first 10 to 15 years after diagnosis.