Cigarette smoking and progression of IgA nephropathy.
BACKGROUND
Multiple community-based cohort studies of mainly middle-aged and elderly populations have shown that cigarette smoking is a risk factor for chronic kidney disease. However, little information is available about an effect of cigarette smoking on progression of primary kidney diseases, including immunoglobulin A (IgA) nephropathy.


METHODS
Retrospective cohort study.


METHODS
971 of 1,001 patients with a diagnosis of IgA nephropathy in 3 major nephrology centers in Osaka, Japan, between 1992 and 2005 who enrolled in the Study of Outcome and Practice Pattern of IgA Nephropathy (STOP-IgAN).


METHODS
Smoking status and number of cigarettes smoked at the time of diagnosis using kidney biopsy. Dose-dependent associations between cigarette smoking and outcomes were assessed in multivariate Cox proportional hazards models. Significantly different clinical characteristics between non-/past and current smokers were controlled for using propensity score-based adjustment, stratification, and matching.


RESULTS
50% increase in serum creatinine level as primary outcome. A composite outcome of a 100% increase in serum creatinine level or end-stage renal disease (ESRD) and ESRD alone as secondary outcomes.


RESULTS
During the median 5.8 years (interquartile range, 2.6-10.2) of the observational period, 117 participants progressed to a 50% increase in serum creatinine level and 47 advanced to ESRD. Multivariate Cox proportional hazards models identified current smokers (HR, 2.03 [95% CI, 1.33-3.10] for primary outcome) and number of cigarettes at kidney biopsy (HR, 1.21 [95% CI, 1.06-1.39] per 10 cigarettes per day) as significant predictors of outcomes. Propensity score-based models confirmed these results. Tests for interaction showed that the association of current smoking with adverse outcomes was stronger in those with lower compared with higher estimated glomerular filtration rates.


CONCLUSIONS
Baseline smoking status was not verified using biochemical tests. Smoking status during the observational period was unavailable.


CONCLUSIONS
Cigarette smoking, in a dose-dependent manner, was identified as a key prognostic factor in IgA nephropathy. Smoking cessation should be encouraged as part of the treatment for IgA nephropathy.
Yamamoto
Ryohei
R
Department of Geriatric Medicine and Nephrology, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.
Nagasawa
Yasuyuki
Y
Shoji
Tatsuya
T
Iwatani
Hirotsugu
H
Hamano
Takayuki
T
Kawada
Noritaka
N
Inoue
Kazunori
K
Uehata
Takuya
T
Kaneko
Tetsuya
T
Okada
Noriyuki
N
Moriyama
Toshiki
T
Horio
Masaru
M
Yamauchi
Atsushi
A
Tsubakihara
Yoshiharu
Y
Imai
Enyu
E
Rakugi
Hiromi
H
Isaka
Yoshitaka
Y
D000328:Adult; D003404:Creatinine / Q000097:blood; D018450:Disease Progression; D015987:Effect Modifier, Epidemiologic; D005260:Female; D005922:Glomerulonephritis, IGA / Q000097:blood / Q000453:epidemiology* / Q000473:pathology*; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood; D016015:Logistic Models; D008875:Middle Aged; D016016:Proportional Hazards Models; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects / Q000453:epidemiology*; D055815:Young Adult
D003404:Creatinine