In this retrospective cohort study of consecutive living kidney donors, we found a relatively low prevalence of cannabis use and cigarette smoking before and after donation. Cannabis use increased after donation. Cannabis use was associated with non-married/common-in-law donors, identifying a salient group for targeting screening and education around cannabis use.

Cannabis use in the Canadian general population had already been increasing with more than 190 000 newly registered medical cannabis users in Canada from June 2014 to June 2018, prior to its legalization in October 2018.¹⁶ In our study, cannabis use among kidney donors within the past 12 months was 15% and was significantly higher after donation than at the time of donation; 10% of former and non-cannabis-using donors started using cannabis after donation. Donors in our study were also interested in increasing cannabis use. Similar to the study by Ruckle et al,¹⁰ cannabis use did not affect kidney function at 3 years of donor follow-up.

Similar to our study findings, the overall smoking prevalence in the general Canadian population is reported to be 15% with 11% being daily smokers.¹⁷ A retrospective, single-center study reported an overall reduction in smoking after donation at 1 year⁶ and another study reported a nonsignificant reduction in smoking with 60% of their donors having less than 2-year follow-up after donation.¹⁸ Close to half of our donors reported having tried to quit in the past year, as in the general population.¹⁷ Post-donation cigarette smoking was statistically associated with non-married/common-in-law status, lower mental health scores, exercise, and household income only on univariate analysis. Multivariate analysis revealed no statistically significant association of these psychosocial factors to cigarette smoking. The lack of statistical association on multivariate analysis may be related to our small sample size. It is also possible that these psychosocial factors are inter-related. Of note, 5% of former and non-smokers at donation started smoking after donation. Unlike a larger study of kidney donors with shorter follow-up and different eGFR estimation, there was no statistical difference in CKD-EPI eGFR after donation among current and former smokers compared with non-smokers at the time of donation in our study.⁴ This may be related to our smaller sample size and potentially underpowered study. Based on the SD of eGFR of 17.7 mL/min/1.73 m² (from our data) and assuming a clinically significant difference of 3 mL/min/1.73 m² between the 2 groups, we would require 548 patients in each group. Importantly, most smokers remained smokers after donation and most donors who quit smoking before donation did not restart after donation.

The strengths of our study include details around smoking and cannabis behaviors before and almost 5 years after kidney donation, the high survey response rate, and robust methodology. Recall bias was minimal given that smoking and cannabis use at the time of kidney donation was not dependent on recall. Our study also examined the associations of smoking and cannabis use to kidney function, psychosocial factors, and mental health—all of which have been identified as priorities to living kidney donors.¹⁹ Limitations of our study include its retrospective nature and selection bias due to single-center study design. Given that we lacked consent to examine data for donors who did not complete the survey, it is possible that smokers were less likely to complete the survey. The number of cannabis users before donation was small. We cannot exclude social desirability bias. Most donors were evaluated prior to cannabis legalization in Canada in October 2018 and may have been less likely to report cannabis use due to fear of being declined for donation. Thus, these donors might have felt more comfortable reporting cannabis use during our survey administration in 2019. Missing cannabis data before donation may have been related to assessments done in earlier years when social work and nephrology consultation notes were not standardized in our donor program. Potential confounding variables, such the presence or absence of household members among non-married donors, were not assessed and may affect our results regarding the association of marital status and cannabis use. Smoking reports before donation may also have been subject to social desirability bias and stigmatization despite smoking not being an absolute contraindication to kidney donation at our center. Smoking is also defined as any amount of exposure without quantification in pack-years.

While data around kidney function among donors who smoke at the time of donation are mixed, kidney donor health maintenance behaviors are important for donor health and should be a prevention goal for the donor team. This is relevant as increasingly medically complex donor candidates come forward and are being accepted as donors. Current guidelines encourage smoking cessation prior to kidney donation, and there are no guidelines around cannabis use.^20,21 Consequently, there is considerable variation around the acceptance of donor candidates who smoke and use cannabis.^22,23 Smoking and cannabis use are not contraindications to kidney donation in our center and are considered on a case-by-case basis in the context of other medical and psychosocial factors. The donor team encourages smoking cessation prior to donation but no formal counseling or pharmacotherapy is provided. Given that most smokers continued to smoke after donation, donor candidates and donor programs must consider that this will remain a serious health risk after donation. This warrants education and support for donor candidates who smoke, to quit smoking prior to donation. Smoking is a modifiable risk factor so cessation may reduce cardiovascular and ESKD risks. Smoking cessation can also reduce future health-related risks regardless of kidney donation.

Regarding follow-up after donation, our center does not complete a focused assessment for health maintenance behavior review but this may be useful as smoking is associated with decreased health-related quality of life and donor death.^3,24 Living kidney donation programs can support smoking cessation by counseling donors about the importance of cessation, directly connecting patients with local or regional smoking cessation programs, and consultation with their primary care physician for possible services offered by their primary care program. The efficacy of smoking cessation programs in the general population is established but studies are needed to determine whether smoking cessation strategies will affect long-term donor outcomes, including ESKD and mortality.²⁵ Given the small number of cannabis users in our study, its impact on kidney function remains unclear. Of concern, the prevalence of cannabis use increased after donation and donors were interested in increasing cannabis use but most donors were unable to quantify their current use. Thus, cannabis use should be determined before and after donation with education of the donor care team to address concerns and questions.