Routine Blood Test Ratio Linked to Higher Mortality Risk in Adults With CKD

A higher ratio of red blood cell distribution width (RDW) to serum albumin was independently associated with increased risks of all-cause, cardiovascular disease (CVD), and cancer mortality among adults with chronic kidney disease (CKD), according to an analysis of nationally representative US data published in Kidney and Blood Pressure Research.¹

Both components of the ratio, known as RAR, come from routine laboratory tests. RDW reflects variation in red blood cell size and has been tied to anemia and inflammation, whereas low albumin signals poor nutritional status.² A prior Japanese cohort linked higher RAR to end-stage kidney disease in patients with CKD,³ but its association with mortality in this population was unknown, the authors noted.

How Researchers Evaluated RAR in Adults With CKD

The researchers analyzed data from 3965 adults with CKD in the National Health and Nutrition Examination Survey (1999-2018), with deaths tracked through December 31, 2019.¹ Consistent with 2024 Kidney Disease: Improving Global Outcomes guidelines, CKD was defined as an estimated glomerular filtration rate below 60 mL/min/1.73 m² or a urine albumin-creatinine ratio above 30 mg/g.

Participants were grouped into RAR quartiles, from below 2.93 in the lowest quartile to 3.45 or higher in the highest. Over a mean follow-up of 88.9 months, 1163 participants died, including 417 from CVD and 231 from cancer.

RAR and All-Cause, CVD, and Cancer Mortality Risk

In the fully adjusted model, each standard deviation increase in RAR was associated with higher risks of all-cause mortality (HR, 1.81; 95% CI, 1.60-2.06; P < .001), CVD mortality (HR, 1.89; 95% CI, 1.59-2.26; P < .001), and cancer mortality (HR, 1.76; 95% CI, 1.46-2.11; P < .001).

Compared with the lowest quartile, the highest quartile carried greater adjusted risks of all-cause (HR, 2.69; 95% CI, 2.09-3.47) and CVD death (HR, 2.86; 95% CI, 1.97-4.13). Results held after propensity score matching.

Relationships were nonlinear for all-cause and CVD mortality and linear for cancer mortality. Threshold analysis identified an inflection point at an RAR of 4.258. Below that value, HRs were 2.32 for both all-cause (95% CI, 1.94-2.76) and CVD mortality (95% CI, 1.73-3.12); above it, the associations were no longer statistically significant.

Subgroup Findings by Albuminuria, Age, and Sex

The link between RAR and all-cause mortality differed by albuminuria level (P for interaction = .012). It was weaker among participants with macroalbuminuria (HR, 1.30; 95% CI, 1.08-1.55) than among those with normoalbuminuria (HR, 2.16; 95% CI, 1.66-2.82) or microalbuminuria (HR, 1.99; 95% CI, 1.66-2.37).

Marked hypoalbuminemia in these patients may obscure the inflammatory signal carried by RDW, the authors suggested. “For patients with macroalbuminuria, the prognostic value of RAR should be interpreted cautiously,” they wrote.

Associations were stronger among adults 65 years or older for all-cause (P for interaction = .007) and cancer mortality (P for interaction < .001) and among men for CVD (P for interaction = .045) and cancer mortality (P for interaction = .006). No significant interaction was observed by level of kidney function.

Limitations and Implications for CKD Risk Stratification

RAR was measured only once, so changes over time were not captured. Unmeasured factors such as iron supplementation and medications may have influenced results, and the observational design limits causal conclusions.

“The present findings indicated that RAR should be interpreted as a prognostic biomarker for mortality outcomes in CKD rather than a modifiable risk factor,” the authors wrote.

Because RDW and albumin are measured in routine, low-cost blood work, the researchers suggested RAR could support mortality risk stratification in CKD. They called for prospective cohorts and randomized trials to confirm the findings.

References

1. Lei K, An X, Chen A, Lin L, Su B, Li Y. Ratio of red blood cell distribution width to albumin level and mortality outcomes in population with chronic kidney disease. Kidney Blood Press Res. Published online September 25, 2026. doi:10.1159/kbr/adjag012

2. Hao M, Jiang S, Tang J, et al. Ratio of red blood cell distribution width to albumin level and risk of mortality. JAMA Netw Open. 2024;7(5):e2413213. doi:10.1001/jamanetworkopen.2024.13213

3. Kimura H, Tanaka K, Saito H, et al. Impact of red blood cell distribution width-albumin ratio on prognosis of patients with CKD. Sci Rep. 2023;13(1):15774. doi:10.1038/s41598-023-42986-2