Monocyte count modifies the association between chronic kidney disease and risk of death

Background: Chronic kidney disease (CKD) is associated with increased all-cause mortality. How non-traditional risk factors modify the mortality risk associated with CKD has not been studied. We approached this question using elevated monocyte count, which is associated with increased risk of death in the general population; however, there is very limited data in CKD. Materials and methods: A national cohort of 1,706,589 U.S. veterans without end-stage renal disease (ESRD) was followed over a median of 9.16 years. Estimated glomerular filtration rate (eGFR; mL/min/1.73m(2)) was divided into 6 categories: 15 - 30, 30 - 45, 45 - 60, 60 - 90, 90 - 105 (reference), and > 105. Monocyte count (k/cmm) was grouped into quartiles: 0.00 - 0.40 (reference), 0.40 - 0.56, 0.56 - 0.70, and > 0.70. Multinomial logistic regression, Cox proportional hazard regression, and formal interaction analyses on both the multiplicative and additive scales were undertaken. Results: Monocyte count > 0.56 k/cmm was associated with increased risk of death overall (hazard ratio (HR) 1.40, confidence interval (CI) 1.38, 1.41 in monocyte quartile 4) and across each eGFR category. Very high (> 105 mL/min/1.73 m(2)) and low (15 - 30 mL/min/1.73m(2)) eGFR categories were associated with increased mortality risk (HR 1.40, CI 1.38, 1.42 and FIR 2.07, CI 2.03, 2.11, respectively). The mortality risk associated with high monocyte count and low eGFR exhibited a strong negative interaction (p < 0.001). No interaction was noted at very high eGFR. Conclusion: While low and very high eGFR were both associated with increased mortality risk, a monocyte count > 0.56 k/cmm only modified the risk associated with low eGFR. This suggests a shared underlying mechanism of death between CKD and high monocyte count.