In this retrospective cohort study, we evaluated the prognostic performance of TG/HDL-C and non-HDL/HDL-C ratios in PD patients to predict OS. An elevated serum TG/HDL-C ratio was most significantly associated with higher all-cause mortality, but also the non-HDL/HDL-C ratio could be identified as an indicator for OS in PD patients. In addition, we developed a novel nomogram incorporating these ratios to improve predictive accuracy.
Dyslipidemia is an important CVD risk factor in the general population and is prevalent in CKD and PD patients2,3. However, in contrast to non-CKD patients serum LDL-C levels have not been identified as a strong risk factor for CVD in end stage renal disease patients undergoing dialysis13,20. Consistently, statin therapy to lower LDL-C did not lead to reduced CVD and mortality in HD patients in respective clinical trials21–23. Independent of LDL-C levels, elevated serum TG and reduced HDL-C have been identified as risk factors for CVD, and the combination of these measures as a TG/HDL-C ratio was found to better predict risk for CVD and mortality than individual markers alone5–7. In CKD, impaired clearance of very low-density lipoproteins (VLDL) and chylomicrons lead to hypertriglyceridemia and deficiency of HDL, with defective HDL antioxidant, anti-inflammatory, and reverse cholesterol transport (RCT) activity24. Consistently, higher TG/HDL-C ratios were associated with the presence of CKD in cross-sectional studies14,15, and predicted the development of CKD in patients with type 2 diabetes25. Prior studies also found a significant association between higher TG/HDL-C ratios and progression of diabetic kidney disease or the risk for CVD events after renal transplantation26,27.
Therefore, several studies investigated whether an elevated TG/HDL-C ratio was also a risk factor for the development of CVD and mortality in the dialysis population, but yielded conflicting results. Indeed, a large retrospective study in incident HD patients demonstrated that a higher TG/HDL-C ratio correlated with reduced CVD and better OS28, indicating a complex and even paradoxical relationship of dyslipidemia and clinical risk in this patient population. In contrast, studies enrolling in part or exclusively PD patients reported a positive association of an increased TG/HDL-C ratio with CVD risk and mortality, particularly in female and older patients12,17, 29. Importantly, the results of our study confirm the independent relationship between a high TG/HDL-C ratio and OS in PD patients. We found that an increased TG/HDL-C ratio was independently correlated with all-cause mortality in PD patients, and the optimal threshold of 1.94 for the TG/HDL-C ratio was the best predictor in terms of hazard ratio (HR), and achieved the highest specificity and sensitivity. However, the applicable cut-off value was different from other studies, which may be due to differences in geographic region and race11. Reasons for the opposing relationship of the TG/HDL-C ratio with CVD risk and mortality in PD versus HD patients are not clear. Interestingly, the TG/HDL-C ratio is also a predictor for insulin resistance30–35, which may be particularly prevalent in PD patients and is associated with an increased risk of hyperglycemia, dyslipidemia, and hypertension, all of which drive CVD mortality.
Our study extends previous findings by additionally identifying the non-HDL-C/HDL-C ratio as a positive predictor for OS in PD patients. Non-HDL-C/HDL-C may correlate better with CVD risk than LDL-C and non-HLD-C levels36. Similar to the TG/HDL-C ratio associations of high non-HDL-C/HDL-C ratios were reported with CVD in the general population19,37, with insulin resistance38, and with CKD in an adult Chinese population15. To the best of our knowledge, this is the first study to demonstrate that the non-HDL/HDL-C ratio is a potential prognostic marker for OS in PD patients. In the current study, a non-HDL/HDL-C ratio ≥ 2.84 was an independent indicator of overall mortality in PD patients after 5 years of follow-up.
However, based on hazard ratios the TG/HDL-C ratio out-performed non-HDL/HDL-C in predicting OS. Further studies are needed to test whether the non-HDL/HDL-C ratio can predict CV outcomes in CKD patients.
As reported previously4–7, 39, low TG/HDL-C and non-HDL-C/HDL-C ratios better predicted OS in this study population than levels of TG, HDL-C and non-HDL-C alone. Indeed, despite the known protective cardiovascular functions of HDL-C, including reverse cholesterol transport, antioxidant, anti-inflammatory and anti-thrombotic properties24, high HDL-C levels did not associate with all-cause mortality in patients with reduced kidney function in a large cohort study40. These observations were supported by studies investigating HDL-C cholesterol efflux capacity (CEC) as a marker of HDL-C functionality, in which CEC did not predict CV events or mortality in dialysis patients41,42. Although high TG and low HDL-C levels were independently associated with mortality in our cohort after multivariate analysis, LDL-C and non-HDL-C were not, despite the predictive value of a higher non-HDL-C/HDL-C ratio. Together, these results suggest that in CKD and PD patients the TG/HDL-C and non-HDL-C/HDL-C ratios better reflect the balance between pro-atherogenic and protective lipoproteins affecting relevant patient outcomes, i.e. CVD and mortality.
Several nomograms have been used to predict disease prognosis based on clinical characteristic, and nomograms were considered to be more precise than a traditional staging system for predicting prognosis in tumors43. However, few studies have demonstrated whether nomograms can predict outcomes in PD patients. The current study established a prognostic nomogram to predict 5-year mortality in PD patients including the TG/HDL-C and non-HDL-C/HDL-C ratios which we identified as independent prognostic markers. The nomogram performed well for OS, which was supported by the obtained c-index (0.795). Our results demonstrated that the derived nomogram could be a valuable tool to predict prognosis in patients undergoing PD.
This study has potential limitations. First, this was a retrospective study based on a single-center database, which may have resulted in bias for data collection and analysis. In addition, no data are available on the relationship between TG/HDL-C or non-HDL/HDL-C ratios with CVD mortality. The optimal cut-off value of TG/HDL-C ratio and non-HDL/HDL-C ratio to predict long-term CV outcome needs further investigations.