Supplementary Material for: Proenkephalin for Cardiovascular and All-Cause Mortality: the REasons for Geographic and Racial Differences in Stroke Study (REGARDS) Study

Introduction: Individuals with kidney dysfunction have greater risk of mortality, especially cardiovascular mortality, but current markers of kidney function, including estimated glomerular filtration rate (eGFR) and urine albumin to creatinine ratio (UACR), may not adequately capture this risk. Proenkephalin (PENK) is an emerging biomarker reflecting kidney glomerular function. We evaluated the association of PENK with all-cause and cardiovascular mortality in The REasons for Geographic and Racial Disparities in Stroke (REGARDS) cohort study and whether associations varied by sex and race. Methods: PENK was measured in 1,021 Black and White participants randomly sampled from REGARDS. We evaluated the association of PENK with all-cause and cardiovascular mortality in nested multivariable Cox-proportional hazard models adjusting for confounders including UACR and eGFR calculated using the 2021 CKD-EPI combined creatinine-cystatin C race-free equation. Effect modification by sex and race was tested. Results: Mean age was 67 years, 50% were women, 50% were Black, mean eGFR was 82 ml/min/1.73m2 and median UACR was 7.7 mg/g. There were 471 deaths and 142 cardiovascular deaths over a median follow-up of 11.6 years. When adjusting for comorbidities and UACR, each doubling of PENK was associated with higher risk of death (HR 1.22, 95% CI 1.00 to 1.48, p=0.05) but this association was not significant after adjusting for eGFR (HR 0.85, 95% CI 0.65 to 1.10, p=0.85). There was a significant interaction by sex (p-interaction=0.004) with higher PENK levels associated with lower mortality in women. PENK was associated with cardiovascular mortality after adjusting for comorbidities and UACR (HR 1.70, 95% CI 1.20 to 2.42, p=0.004), but this was not significant when adjusting for eGFR (HR 1.36, 95% CI 0.84 to 2.21, p=0.20). There was no significant interaction by sex or race. Conclusion: PENK does not provide additional risk stratification for all-cause and cardiovascular mortality beyond current biomarker measures of eGFR.